IBM8FD.WS4     (=IBM 8" Floppy Diskette)
----------

"The IBM Diskette General Information Manual"
 IBM Document GA21-9182-4
 Fifth Edition: August 1979

(Retyped by Emmanuel ROCHE. Posted to comp.os.cpm.amethyst by Roche
on 26 May 2006.)


Preface
-------

This  publication  is intended for use by anyone  who  uses  IBM
diskettes, or who is interested in learning about or using them.
You  are not required to have any prior knowledge of  diskettes,
but  you  are  expected  to  have  a  basic  knowledge  of  data
processing.  To  help  you  learn  about  IBM  diskettes,   this
publication provides:

      - General  information about the advantages of  diskettes,
        their uses, and their physical appearance.

      - Some suggestions for handling and replacing diskettes.

      - Some basic information about the location and addressing
        of the data on the diskette.

      - Detailed information about the systems and devices  that
        use IBM diskettes and how the diskettes are organized.

In  this  manual, the term system or IBM system  includes  those
devices that use diskettes but are not, by definition, systems.


Related publications
--------------------

This  publication  is designed to  present  general  information
about IBM diskettes. For more specific information about the way
diskettes   are  used  in  individual  systems,  refer  to   the
appropriate    system   documentation.    Generally,    diskette
information appears in publications such as:

      - Operator's guides

      - System summaries

      - Functions reference manuals

      - System introductions

      - Component descriptions

      - Customer setup manuals


Contents
--------

INTRODUCTION
The IBM diskette
The advantages of diskettes
The purposes for diskettes

THE PHYSICAL FEATURES OF DISKETTES
The protective envelope
The identifying and operating features
    The identifying features
    The operating features
The diskette drive

DISKETTE HANDLING
Conserving information
Inserting diskettes
Removing diskettes
Labeling diskettes
Storing diskettes
    Environmental requirements
    Diskette magazine storage
    Short-term storage
    Long-term storage
Shipping diskettes

REPLACING DISKETTES
Damaged diskettes
Worn diskettes
Suggestions for diskette operations

DISKETTE ADDRESSING AND LAYOUT
The track
The cylinder
The head
The sector
The address
    The index cylinder
    Alternative cylinders

IBM DISKETTE TYPES
IBM diskette 1
    128 bytes per sector
    256 bytes per sector
    512 bytes per sector
IBM diskette 2
    128 bytes per sector
    256 bytes per sector
IBM diskette 2D
    256 bytes per sector
    512 bytes per sector
    1024 bytes per sector

ACCESSORIES, DISKETTES, AND SUPPLIES

APPENDIX A. DISKETTE USERS
IBM diskette 1
IBM diskette 2
IBM diskette 2D

APPENDIX B. DATA ORGANIZATION
Physical and logical records
Blocking and spanning
Sequential data

APPENDIX C. INITIALIZATION AND TRACK FORMAT
Initialization
Track format

APPENDIX D. INDEX CYLINDER LAYOUT

APPENDIX E. DATA SET LABEL LAYOUT

APPENDIX F. DATA EXCHANGE
Basic data exchange
Type H data exchange
Type E general exchange

APPENDIX G. GLOSSARY

INDEX


INTRODUCTION
------------

The IBM diskette
----------------

The IBM diskette is a small, convenient, storage medium for  use
on various data processing systems and devices. The IBM diskette
is  composed  of two parts: the semirigid  plastic  jacket  that
protects  the  disk,  and, sealed inside  the  jacket,  a  thin,
flexible  disk  that turns freely inside the jacket.  The  disk,
coated with a magnetic material, provides the recording surfaces
of the diskette. These surfaces are kept clean by a low-friction
liner in the jacket.

The  diskette is ordinarily used singly. However, there are  IBM
systems that use diskettes enclosed in containers that can  hold
up to 10 diskettes. These containers are called magazines.  When
it  is  used in a system, the entire magazine  slides  into  the
diskette drive. (A diskette drive is the device that reads  from
or writes on diskettes.)


The advantages of diskettes
---------------------------

For  years,  the  primary  permanent  storage  device  in   data
processing  was the punched card. Eventually,  however,  storing
the  great  quantities of punched cards needed  to  maintain  an
active  system  became  a  burden.  The  diskette  provides  one
solution to the storage problem, but there are other  advantages
in using diskettes:

      - Diskettes can contain more information than cards.

        The  amount  of  information  that  can  be  stored   on
        individual  diskettes  is many times  greater  than  the
        amount  of information that can be stored on  individual
        cards.

      - Diskettes  can  be rewritten many times;  cards  can  be
        completely punched only once.

        Diskettes  can be reused to store new information  after
        the information they contain is no longer needed.  Cards
        cannot  be punched a second time; once  the  information
        they  contain is obsolete, the cards must be  stored  or
        thrown away.

      - Diskettes can be corrected, but the information on cards
        cannot be changed.

        Incorrect data on diskettes can be corrected by  placing
        the  correct  information in  the  locations  containing
        incorrect  information.  This  is  a  simple   rewriting
        process.  Because  holes are punched in cards  to  store
        information,  new  cards  must  be  punched  to  correct
        errors.

      - Diskettes are easier to handle than cards.

        The  information stored on diskettes can be more  easily
        moved,  stored,  and  mailed than  the  same  amount  of
        information stored on cards.


The purposes for diskettes
--------------------------

Diskettes  can  be used as storage media for  various  kinds  of
information. The particular purpose for the diskette varies with
the application for which the diskette is used in any particular
system.  Because  of  these variations,  this  manual  makes  no
attempt to list every possible use for diskettes, but among  the
more standard uses are:

      - Storing data for exchange between devices or systems

      - Saving  system  data,  offline, to be  restored  to  the
        system at a later time as needed

      - Logging or buffering transaction data for batch processing

      - Processing  system data (usually in small systems or  in
        control units)

      - Storing and loading system microcode

      - Distributing programs

      - Storing and loading diagnostic information

Some  systems  and  devices have diskette drives  that  are  not
accessible  to  the  operator. The  diskettes  in  these  drives
usually  contain microcode or diagnostic information for use  in
the particular systems or devices.

Because  the uses for diskettes vary from system to system,  IBM
produces  diskettes  of varying types and  capacities.  Briefly,
there are three basic types of diskettes, they are:

      - IBM  diskette 1. This diskette contains  information  on
        one side only.

      - IBM  diskette 2. This diskette contains  information  on
        both sides.

      - IBM  diskette  2D. This  diskette  contains  information
        written  in double-density encoding (twice the  standard
        number of bits written on a given track) on both sides.

A  complete  description  of the  diskettes  is  provided  under
"Diskette types", later in this manual.


THE PHYSICAL FEATURES OF DISKETTES
----------------------------------

Physical features are those characteristics that make any object
consistently  recognizable. The protective envelope and all  the
various  labels, holes, slots, notches, and dimensions form  the
physical features of the IBM diskette.


The protective envelope
-----------------------

The  protective  envelope  is  an  essential  part  of  all  IBM
diskettes,  even though you must remove the envelope before  you
can  put  the  diskette in the diskette  drive.  The  object  of
protecting a diskette is to protect the information contained on
that diskette.

Except  when  it  is in the diskette drive or  a  magazine,  the
diskette should always be in its protective envelope.

An   unprotected   diskette  is  stored  information   that   is
vulnerable. The information is subject to unknown alteration  or
destruction from many sources. Some examples of things that  can
damage  diskettes  that have been left out of  their  protective
envelope  are:  fingerprints, smoke,  sneezes,  spilled  drinks,
coughs, dust, and ashes. (Diskette damage is discussed in detail
under "Diskette handling", later in this manual.)


The identifying and operating features
--------------------------------------

The  remaining  features are part of the  diskette  itself.  The
identifying  features  are for your use while  the  diskette  is
outside the diskette drive, and are visible when the diskette is
in  its  protective envelope. The operating features  are  those
features that allow the diskette to be read from or written upon
while it is inside the diskette drive.


The identifying features
------------------------

There   are  diskette  labels  on  which  you  can  record   the
descriptive,  operational, and historical information  that  you
want  to  remain with the diskette. Further information  on  the
labels  is  provided under "Labeling diskettes"  later  in  this
manual.

     1. Permanent  diskette  label (Square label at  upper  left
        corner)

        Use  this  label to record  information  describing  the
        diskette and its condition. Record information such as:

        - The serial number (volume ID; see Appendix D)

        - The date you first used the diskette

        - The location of any defective cylinders

     2. Temporary identification label (Horizontal label at top)

        Use this adhesive label to record changing items such as:

        -  The data stored on the diskette; job numbers,  names,
        and dates

        -  The  identification  of the person  who  entered  the
        information

        - The date of data verification

        - The device used to write the information on the diskette


The operating features
----------------------

Each of these features contributes in some way to the  operation
of the diskette when it is in the diskette drive. The  operating
features are holes in the diskette jacket, and two of the  holes
extend through the disk that is sealed inside the tacket.

     1. Index hole

        There  is an index hole that passes  completely  through
        the  diskette.  When  the diskette is  in  the  diskette
        drive,  the  disk  turns inside  the  jacket.  Once  per
        revolution, the holes in the disk and the jacket line up
        and  allow  a beam of light to shine through  the  index
        hole.  The light beam is used for a number of  purposes,
        some of which are:

        - Timing for various functions within the diskette drive

        - Verifying that the diskette is of the correct type for
        the diskette drive

        -  Verifying that the diskette is properly installed  in
        the diskette drive

        - Providing timing and synchronizing for  communications
        between the system or device and the diskette drive

        The index holes on one-sided and two-sided diskettes  do
        not occupy the same location on the diskette. The  index
        hole is centered (at 12 o'clock) on one-sided diskettes,
        and  is offset to the right (at 1 o'clock) on  two-sided
        diskettes.

     2. Drive spindle hole

        The diskette drive spindle requires that there be a hole
        in  both  the diskette jacket and the  disk  inside  the
        jacket.  When  the diskette is seated  in  the  diskette
        drive,  the drive spindle moves into the  drive  spindle
        hole  and clamps to the disk, causing the disk to  begin
        turning.

     3. Head slot

        The  head  slot  exposes the recording  surface  of  the
        diskette to the read/write head. There is a head slot on
        both  sides  of each type of diskette.  On  a  one-sided
        diskette,  a pressure pad enters the head slot  opposite
        the  read/write head. On a two-sided diskette,  data  is
        recorded on both sides of the diskette, so a  read/write
        head enters both head slots.

     4. Stress relief notches

        The stress relief notches in the diskette jacket aid  in
        distributing  the stresses that occur in the  head  slot
        area if the diskette is accidentally bent.


The diskette drive
------------------

The diskette drive provides the means for reading or writing  on
the  diskette. Under control of the system, the  diskette  drive
transfers  encoded information to or from the diskette by  using
an   electromagnetic  read/write  head.  The  drive  moves   the
read/write head into position on the moving recording surface of
the  diskette,  and  writes magnetically  charged  spots  (small
magnetic  fields)  at  specific  locations  (addresses)  on  the
recording surface. The information written at an address remains
there  until  it  has been replaced by new  information,  or  is
magnetically erased.

To  read  from  the  diskette,  the  diskette  drive  moves  the
read/write head to the proper position on the diskette recording
surface, finds the proper address, and senses and transmits  the
information to the system.

Because  there are diskettes that can store information on  both
sides,  some diskette drives have two read/write heads,  one  on
each side of the diskette.


DISKETTE HANDLING
-----------------

IBM  diskettes are designed to withstand the stresses of  normal
and frequent handling. However, there are some precautions  that
you  should  note  as  you handle  your  diskettes.  By  careful
observance   of   these  precautions,   and   guarding   against
carelessness  in everyday use, your diskettes will provide  long
and reliable service.

The proper way to remove a diskette from its protective envelope
is  to grasp the diskette by its upper edge, and pull it out  of
the envelope.

Be sure to keep the protective envelope and return the  diskette
to  the  envelope every time you remove the  diskette  from  the
diskette drive. As its name implies, the protective envelope  is
provided to help prevent damage to the diskette. The damage on a
diskette can cause problems that range from intermittent reading
or  writing  errors  to  a permanent  loss  of  the  information
contained on the diskette.


Conserving information
----------------------

When  a  diskette  is damaged  or  mishandled,  the  information
contained on that diskette can be lost or altered. The following
paragraphs point out some of the more common handling  mistakes.
These  mistakes  are  almost always the  result  of  a  moment's
carelessness.   Diskettes   are  not,  in   themselves,   highly
expensive;  but the information they contain can be very  costly
if it is lost.

Diskettes  can  be  damaged  in many ways.  They  can  be  bent,
creased, warped, dented, contaminated, or magnetically altered.


Bent diskettes

IBM diskettes are made to be flexible, but the flexibility is to
allow  the  diskette  to function more freely  in  the  diskette
drive.   Diskettes  should  not  be  grasped   too   vigorously,
especially near the head slot, nor should paper clips or  rubber
bands  be  placed on them. The bending caused by  any  of  these
actions can be permanent.


Creased diskettes

Folding  a diskette or placing heavy objects on it can cause  it
to be creased. A crease is permanent, and ruins the diskette.


Warped diskettes

Warping  is  usually  the result of  exposing  the  diskette  to
temperatures   above   the  safe   limit   (see   "Environmental
requirements", later in this chapter). However, there are  other
causes  for  warping  also. A diskette that is held  in  a  bent
position for too long will warp. Improper storing can also cause
diskettes  to warp. A diskette that is warped will never  return
to its original shape.


Dented diskettes

You  should  use  a fiber-tip pen to mark  on  diskette  labels.
Pressure  from  a  ball  point pen  might  cause  dents  in  the
recording surface. Dents result in lost information because  the
read/write head loses contact with the recording surface.

Pencils  are  not  recommended because they  are  erasable.  You
should never erase on a diskette because the eraser dust can get
inside  the  diskette  jacket  and  contaminate  the   recording
surface. Contamination is discussed in the next paragraph.


Contaminated diskettes

A  diskette  is  damaged by  contamination  when  the  recording
surface  is  touched, spotted, or dampened by an  oily,  sticky,
magnetic, abrasive, or, in some cases, a non-abrasive substance.
Examples of these substances are:

        - Fingerprints or smoke (oily)

        - Soft drinks or coffee (sticky)

        - Ferrous dust or filings (magnetic)

        - Dust or filings (abrasive)

        - Pencil eraser dust (non-abrasive)


Magnetically altered diskettes

Do  not place magnets or magnetized objects near  the  diskette.
The  magnetic  field produced by these magnets  can  effectively
erase information from the surface of the diskette. The diskette
does  not  suffer any physical damage, but  the  information  it
contains may no longer be accurate.


Inserting diskettes
-------------------

The  method  by which the diskette is locked into  the  diskette
drive  varies  with the type of diskette drive you  have.  There
are, however, some general statements that should be made  about
diskette  insertion. Always exercise care in placing a  diskette
in a diskette drive or in a diskette magazine. Be sure you:

     1. Carefully  remove  the  diskette  from  its   protective
        envelope.  Be  careful not to touch any of  the  exposed
        areas of the recording surface.

     2. Without  bending the diskette, slowly push the  diskette
        into the diskette drive or magazine until it stops.

     3. Slowly  close  the  diskette drive  cover  or  move  the
        diskette locking lever.


Removing diskettes
------------------

Always  exercise care when removing a diskette from  a  diskette
drive or a diskette magazine. Depending on the type of  diskette
drive you have, be sure you:

     1. Completely  open  the  diskette drive  cover,  move  the
        diskette  locking lever as far as it will go,  or  lower
        the diskette magazine retaining spring.

     2. Without  bending the diskette, slowly pull the  diskette
        completely  clear of the diskette drive or magazine.  Be
        careful  not  to touch any of the exposed areas  of  the
        recording surface.

     3. Carefully  put  the diskette back  into  its  protective
        envelope.


Labeling diskettes
------------------

There  are two labels provided for each diskette. The  permanent
labels  are  already attached to the diskette jackets,  and  the
temporary  labels  come  in  a packet  with  each  order  of  10
diskettes.  The temporary labels come in five different  colors:
red,  blue,  green, yellow, and gray. The colors  allow  you  to
identify the various types of information without having to read
the  labels. A description of the two labels, and some  examples
of  the  kinds of entries you could make on  them,  is  provided
under  "The  physical features of diskettes",  earlier  in  this
manual.

As discussed under "Diskette handling", earlier in this  manual,
a  fiber-tip pen is the only recommended writing instrument  for
marking on the diskette labels. Always have the diskette in  its
protective  envelope  when you are writing on the  labels;  your
hand  or  wrist could accidentally contact and  contaminate  the
recording  surface.  The envelope is cut away to permit  you  to
write on either label.

When  starting a new job on a diskette, cross out,  rather  than
erase,  the  old  information on the label (the  dust  from  the
erasure  can get inside the diskette jacket and contaminate  the
recording surface). When the label is full, remove it and attach
a  new  one. Do not put new labels over old  ones,  because  the
label buildup can affect the performance of the diskette  drive.
Do  not attach labels to the reverse side of the jacket, and  do
not cover any of the holes.

Replace  the temporary labels every 6 months, even of  they  are
not  filled.  Otherwise, the adhesive can harden  and  make  the
label difficult to remove.

If  you  wish,  you  can attach  the  temporary  labels  to  the
protective  envelope, instead of the diskette jacket. Write  the
diskette  serial  number on the envelope and  on  the  permanent
label, to ensure that you will always return the diskette to the
correct envelope.


Storing diskettes
-----------------

Environmental requirements
--------------------------

Temperature:  10 degrees C to 51 degrees C (50 degrees F to  125
degrees F)

Relative humidity: 8% to 80%

Maximum wet bulb temperature: 29 degrees C (85 degrees F)

CAUTION
If  a  diskette  has  been  stored  in  an  area  in  which  the
temperature is markedly different from the operating temperature
of the diskette drive, do the following:

     1. Remove the diskette from its shipping container.

     2. Wait  5  minutes  for  the diskette  to  adjust  to  the
        operating  temperature of the diskette drive.  You  must
        wait  longer  if  you are  using  a  diskette  magazine,
        because   the  diskettes  are  closely  packed  in   the
        magazine, and will change temperature more slowly.


Diskette magazine storage

Store  diskette  magazines  so they  stand  vertically.  If  the
magazines  contain  diskettes,  be sure to put the  lid  on  the
magazine to lock the diskettes in position and inhibit warping.


Short-term storage

You may store diskettes flat in their envelopes, in stacks of 10
or  less, when you need the diskettes for immediate use. If  you
store the diskettes vertically, support them so they do not lean
or sag.


Long-term storage

If you do not need the diskettes immediately, you may store them
in  their original shipping cartons, with each diskette  in  its
protective  envelope.  Shipping  cartons can  be  stored  either
vertically or horizontally.

Note:  Do not apply pressure to diskette envelopes  or  cartons,
because pressure can warp the diskettes.


Shipping diskettes
------------------

When  shipping  a  diskette, always label the  package  "DO  NOT
EXPOSE  TO HEAT OR SUNLIGHT". When receiving a  diskette,  check
the  carton and the diskette for possible damage. Diskettes  can
be  safely  exposed  to temperatures from  -40  degrees  C  (-40
degrees F) to 51 degrees C (125 degrees F) during shipment.

See  "Diskettes,  supplies, and accessories" for a list  of  the
shipping  and  packing  materials available from  your  IBM  IRD
(Information Records Division) representative.

To pack one diskette:

      - Place the diskette in its protective envelope.

      - Put the envelope in a single-diskette carton.

To pack multiples of 10 diskettes:

      - Place each diskette in its protective envelope.

      - Put 10 diskettes in a 10-pack.

      - Put  each  10-pack between spacers,  to  prevent  damage
        during shipping.

      - Insert top and bottom pads in the carton.

      - Place the 10-packs and their spacers in the  appropriate
        sized carton.

        CAUTION
        Do not use so much filler that the diskettes are tightly
        compressed; compression can warp the diskettes.

      - Fill the open space in partially filled cartons and  10-
        packs with a filler that cannot contaminate the diskette
        or enter the diskette jacket.


REPLACING DISKETTES
-------------------

You  can  prevent most problems from occurring  by  periodically
examining your diskettes, handling them carefully (see "Diskette
handling",  earlier  in this manual), and  replacing  them  when
necessary.  This chapter offers some things you should look  for
and  some suggestions that might help you know when  replacement
is needed.


Damaged diskettes
-----------------

You should replace diskettes that are:

        - Folded

        - Creased

        - Warped

        - Dented

        - Contaminated

        - Scratched

You may be able to recover the information from a diskette  that
has  not been folded or warped if the damage is not too  severe.
The  disk  must be free to turn inside the  diskette  jacket  in
order  to recover the information. After you have recovered  the
information  from  the diskette, however,  discard  the  damaged
diskette.

Carefully  examine any diskette that you suspect may  have  been
exposed to excessively high temperatures.

You  may be able to detect dents by turning the disk inside  the
diskette jacket and carefully examining the recording surface.

Note: If you try to turn the disk inside the diskette jacket, be
very careful not to touch any portion of the recording  surface.
Any  fingerprints  on that surface contaminate the  surface  and
ruin the diskette.

If you insert a contaminated diskette into a diskette drive, the
contaminants can be transferred to the read/write head and  from
the  read/write head to the next diskette to be inserted in  the
drive. The read/write head may also be damaged.

You may be able to recover the information from a diskette  that
has  had a substance spilled on it if you are positive that  you
can  rinse  or  wipe the substance  from  the  diskette  without
scratching  the recording surface or leaving a residue.  If  you
are  not sure, do not try to use the diskette. If you  know  you
can rinse the substance away, use only clean, cool water. Again,
be  careful  not  to  scratch  the  recording  surface  or   get
fingerprints  on  it. Any kind of cleanser can  contaminate  the
diskette,  and  warm water can warp the diskette.  Solvents  can
dissolve and ruin the recording surface.


Worn diskettes
--------------

When  diskettes  are used for data exchange as defined  in  this
manual,  recording  surface  wear is  not  a  frequent  problem.
However,  because  the read/write head is in  contact  with  the
recording  surface when reading or writing, wear does  occur  on
the  surface  over a period of time. Eventually, this  wear  can
cause  areas on the recording surface in which readable  records
cannot be written. (Of course, the handling, contamination,  and
environmental  concerns  discussed earlier in this  manual  also
affect the length of time a diskette can remain in service.)

Some  systems use diskettes to store the active processing  file
for  the  system.  When the diskette is used in  this  way,  the
read/write  head is repeatedly lowered to the diskette  surface.
The  repeated  loading of the read/write head can  increase  the
wear  rate.  Ultimately,  aside fom external  factors,  wear  is
dependent  upon the total usage of the individual tracks on  the
diskette.


Suggestions for diskette operations
-----------------------------------

Your  diskette  operations will be smoother if you  establish  a
routine for tracking your diskettes, and learning  approximately
how much service you can expect from each of them. The following
suggestions can help you set up and run your operation:

      - Before  using a new diskette, assign a serial number  to
        it,  and  record the number on  the  permanent  diskette
        label and in the space provided in the volume ID  field.
        (See Appendix C.)

      - Keep  a log of your diskettes by serial number  and  the
        date you first used the diskette.

      - Use   your   diskette  log  in  combination   with   the
        information on the diskette labels to track the  average
        length  of  time you receive satisfactory  service  from
        your diskettes.

      - Distribute  your information over the diskette, so  that
        reading  and  writing occur over  the  entire  recording
        surface.

      - Be prepared to handle unexpected problems. Some diskette
        problems,  especially those related to diskette  damage,
        are unpredictable, and can occur at any time.

      - Make provision for an adequate recovery plan. Know  what
        you  must  do to ensure that your vital  information  is
        safe. If necessary, make duplicate diskettes.

If  a diskette causes error, you probably will have  to  replace
it. If your system allows you to reinitialize, try that, but  if
the errors persist, discard the diskette. (See Appendix C.)


DISKETTE ADDRESSING AND LAYOUT
------------------------------

Diskettes  contain  libraries, or parts of libraries,  in  which
information is stored for safekeeping until needed. The  concept
of  a library also bears with it the idea that  any  information
stored   there   is   accessible   upon   demand.    Information
accessibility,  then, requires a form of addressing that can  be
used  to find the information quickly. An address on a  diskette
is  composed  of a track or cylinder number, a  read/write  head
number, and a record or sector number. Each of these numbers  is
described in the following paragraphs.


The track
---------

Everything  stored  on the diskette is in the  form  of  records
whose  primary  address  is the track or  cylinder  number  (the
cylinder concept is described later in this manual).

The  diskette  drive  contains  a carriage  that  can  move  the
read/write head to any of 77 distinct positions on the  diskette
recording surface. A distinct movement of the read/write head is
required to get from one position to the next; therefore, if the
read/write  head  is  held  stationary  in  one  position  after
another,  the path formed on the surface of the turning disk  is
one of concentric circles, not a spiral. Each of the  concentric
circles  is  a track. For addressing purposes,  the  tracks  are
numbered from 00 through 76.

On  a  one-sided diskette, information is recorded on  only  one
side  of the diskette; on a two-sided diskette,  information  is
recorded  on both sides. The label side of a two-sided  diskette
is  side  1; the opposite side is side 0. A  one-sided  diskette
uses side 0 only. The diskette drive for two-sided diskettes has
a  read/write head on each side of the diskette. Each  track  on
side  0 of a two-sided diskette has an associated track on  side
1.  The  read/write  heads are numbered  to  correspond  to  the
diskette side number.


The cylinder
------------

The name cylinder refers to both of the tracks available to  the
read/write  heads  at any of the 77 locations on  the  two-sided
diskette.   (Note  that  the  terms  track  and   cylinder   are
interchangeable.  Cylinder  is also used to refer to  the  track
locations  on  a one-sided diskette.) The idea of  the  cylinder
comes  from  the imaginary, geometric figure formed  by  a  line
drawn  between the two read/write heads (through  the  diskette)
when  the  heads are stationary over  their  respective,  moving
tracks.  As  the  diskette moves between  the  heads,  the  line
between  the  heads  forms a truncated  cylinder.  The  cylinder
concept  applies to any of the 77 tracks. Because the track  and
cylinder  locations are identical, cylinder addresses  are  also
numbered from 00 through 76.

The  time  saved justifies the use of the cylinder  concept.  It
takes time for the access mechanism to move the read/write heads
from track to track. However, by using an addressing scheme that
reads  or  writes first one side of the diskette  and  then  the
other, two tracks can be utilized without moving the heads.  The
diskette  drive  switches  from  head  to  head  electronically.
Compared  with any mechanical movement, electronic switching  is
almost instantaneous.


The head
--------

The  term head refers to the read/write head (or heads)  in  the
diskette  drive.  The read/write heads are described  in  detail
under "The diskette drive", earlier in this manual. The  concept
of  electronic  head switching was mentioned  in  the  preceding
paragraph.

The head number is either a hex 00 or a hex 01 to correspond  to
the  side  of the diskette the read/write head is on.  The  head
number is always hex 00 on one-sided diskettes.


The sector
----------

To allow increasingly specific addressing, the track or cylinder
is  uniformly divided into arcs called sectors. Each  sector  is
addressable.

Cylinder 0, side 0 always contains 26 sectors with 128 bytes per
sector. The number of sectors on cylinders 1 through 76  depends
on the diskette type and the number of bytes per sector for that
diskette type (see "IBM diskette types", later in this manual).


The address
-----------

In  format,  the  address  of any record  on  a  diskette  is  a
composite  of  the elements of addressing  just  discussed:  the
track  or cylinder number, the read/write head number,  and  the
record  or sector number. Each of these numbers is  a  two-digit
hexadecimal  value.  The digits are arranged in the  address  in
order of increasing definition. (In the following  illustration,
X = a hexadecimal digit.)

  +-------------> This is the number of the cylinder on which
  |               the record is to be written, or from which
  |               the record is to be read.
  |
  |   +---------> This number specifies the read/write head
  |   |           and, by doing that, also specifies which
  |   |           side of the diskette is to be used.
  |   |
  |   |   +-----> This is the number of the sector on which
  |   |   |       the record is to be written, or from which
  |   |   |       the record is to be read.
| XX  XX  XX |
+------------+--> This is the complete address.


The index cylinder
------------------

Cylinder  0  is the outermost cylinder on the diskette,  and  is
called  the  index  cylinder.  This  cylinder  is  reserved  for
information  that describes the diskette and its  contents.  The
descriptive    information    includes    volume    and    owner
identification,  and other information associated with data  set
(a  group of related records) on the diskette.  The  information
about  the data sets includes the name of the data set  and  the
address associated with the data set.

The  continuous space occupied by or reserved for  a  particular
data  set is called an extent. Extents also use  addressing,  to
achieve efficient reading and writing operations.

The  address  at the beginning of the extent is called  the  BOE
(beginning  of extent). The address at the end of the extent  is
called  the EOE (end of extent). If a data set does not use  all
of the space alloted to it by the BOE and EOE addresses, another
address for the end of the data is called the EOD (end of data).
The  EOD  address  identifies the next unused  area  within  the
extent,  or  shows  that the data has been written  to  the  EOE
address.  The following illustration shows the relationships  of
the BOE, EOD, and EOE.

        This is the actual space currently
        being used for the data set.
               |
        +------+-------+
       BOE            EOD  EOE
        |              |    |
        V              V    V
-------------------------------------
        +--------+----------+
                 |
        This is the extent
        (the area allotted for the data set).


Alternative cylinders
---------------------

The last two cylinders on the diskette, 75 and 76, are  reserved
as  alternative cylinders. That is, these cylinders are used  as
replacements  for  cylinders  that  are  defective.  These   two
cylinders  are not used for storing information until  they  are
used as alternative cylinders.


IBM DISKETTE TYPES
------------------

IBM diskette 1
--------------

The  IBM diskette 1, also known as a one-sided diskette,  has  a
recording  surface on one side only. Because the diskette  drive
can have a read/write head that contacts both sides, the side of
the  diskette  that is opposite the recording  surface  is  also
finished to a smooth surface. The IBM diskette 1 is available in
three formats: 128, 256, and 512 bytes per sector.


128 bytes per sector
--------------------

(IBM Part 2305830)

This diskette has 77 tracks (00 through 76), with one track  per
cylinder.  Each cylinder on this diskette, including  the  index
cylinder (00), consists of 26 sectors with 128 bytes per sector.
Cylinders  1  through 74 are available for user  data  providing
1924 sectors or 246,272 bytes. Cylinders 75 and 76 are  reserved
for alternative cylinder assignment.

When this diskette is used for basic data exchange, 73 cylinders
(1  through 73) are used. Cylinder 74 is not used. A basic  data
exchange diskette provides 1898 sectors or 242,944 bytes.


256 bytes per sector
--------------------

(IBM Part 2305845)

This diskette has 77 tracks (00 through 76), with one track  per
cylinder.  The index cylinder (00) consists of 26  sectors  with
128 bytes per sector. Cylinders 1 through 76 have 15 sectors per
cylinder. Each sector is 256 bytes long. Cylinders 1 through  74
are  available for user data providing 1110 sectors  or  284,160
bytes. Cylinders 75 and 76 are reserved for alternative cylinder
assignment.


512 bytes per sector
--------------------

(IBM Part 1669954)

This diskette has 77 tracks (00 through 76), with one track  per
cylinder.  The index cylinder (00) consists of 26  sectors  with
128 bytes per sector. Cylinders 1 through 76 have 8 sectors  per
cylinder. Each sector is 512 bytes long. Cylinders 1 through  74
are  available  for user data providing 592 sectors  or  303,104
bytes. Cylinders 75 and 76 are reserved for alternative cylinder
assignment.


IBM diskette 2
--------------

The  IBM diskette 2, also known as a two-sided diskette,  has  a
recording surface on each side. The IBM diskette 2 is  available
in two formats: 128 and 256 bytes per sector.


128 bytes per sector
--------------------

(IBM Part 1766870)

This  diskette  has  77 cylinders (00  through  76).  The  index
cylinder  (00) consists of 26 sectors with 128 bytes per  sector
on  each  side  of  the diskette for  a  total  of  52  sectors.
Cylinders  1 through 76 each have 26 sectors with 128 bytes  per
sector  on each side of the diskette for a total of  52  sectors
per  cylinder. Cylinders 1 through 74 are available  as  primary
cylinders  for  data providing 3848 sectors  or  492,544  bytes.
Cylinders  75  and  76 are  reserved  for  alternative  cylinder
assignment.


256 bytes per sector
--------------------

(IBM Part 2736700)

This  diskette  has  77 cylinders (00  through  76).  The  index
cylinder  (00) consists of 26 sectors with 128 bytes per  sector
on  each  side  of  the diskette for  a  total  of  52  sectors.
Cylinders  1 through 76 each have 15 sectors with 256 bytes  per
sector  on each side of the diskette for a total of  30  sectors
per  cylinder. Cylinders 1 through 74 are available  as  primary
cylinders  for  data providing 2220 sectors  or  568,320  bytes.
Cylinders  75  and  76 are  reserved  for  alternative  cylinder
assignment.


IBM diskette 2D
---------------

The  IBM  diskette 2D is a two-sided,  double-density  diskette.
Two-sided,  of course, means that the diskette has  a  recording
surface on each side. Double density means that the bits on this
diskette are written at twice the density of the bits on the IBM
diskettes 1 and 2.


256 bytes per sector
--------------------

(IBM Part 1766872)

This  diskette  has  77 cylinders (00  through  76).  The  index
cylinder  (00) consists of 26 sectors with 128 bytes per  sector
on  side 0 and 26 sectors with 256 bytes per sector on  side  1,
for  a total of 52 sectors. Each 256-byte sector on  cylinder  0
contains  two 128-byte data set labels. Cylinders 1  through  76
each  have 26 sectors with 256 bytes per sector on each side  of
the diskette for a total of 52 sectors per cylinder. Cylinders 1
through 74 are available as primary cylinders for data providing
3848 sectors or 985,088 bytes. Cylinders 75 and 76 are  reserved
for alternative cylinder assignment.


512 bytes per sector
--------------------

(IBM Part 1669044)

This  diskette  has  77 cylinders (00  through  76).  The  index
cylinder  (00) consists of 26 sectors with 128 bytes per  sector
on  side 0 and 26 sectors with 256 bytes per sector on  side  1,
for  a total of 52 sectors. Each 256-byte sector on  cylinder  0
contains  two 128-byte data set labels. Cylinders 1  through  76
each  have 15 sectors with 512 bytes per sector on each side  of
the diskette for a total of 30 sectors per cylinder. Cylinders 1
through 74 are available as primary cylinders for data providing
2220  sectors  or  1,136,640  bytes. Cylinders  75  and  76  are
reserved for alternative cylinder assignment.


1024 bytes per sector
---------------------

(IBM Part 1669045)

This  diskette  has  77 cylinders (00  through  76).  The  index
cylinder  (00) consists of 26 sectors with 128 bytes per  sector
on  side 0 and 26 sectors with 256 bytes per sector on  side  1,
for  a total of 52 sectors. Each 256-byte sector on  cylinder  0
contains  two 128-byte data set labels. Cylinders 1  through  76
each  have 8 sectors with 1024 bytes per sector on each side  of
the diskette for a total of 16 sectors per cylinder. Cylinders 1
through 74 are available as primary cylinders for data providing
1184  sectors  or  1,212,416  bytes. Cylinders  75  and  76  are
reserved for alternative cylinder assignment.


ACCESSORIES, DISKETTES, AND SUPPLIES
------------------------------------

IBM produces many supplies that are related directly to diskette
use.  These  supplies include items you can  use  for  shipping,
storing,  or working with diskettes. Your IBM  IRD  (Information
Records  Division) representative can furnish these supplies  to
you.

                                    Sold in
Accessory                         multiples of  Weight
--------------------------------  ------------  ----------------
Desk stand        (20 diskettes)        1       2.9 kg (6.5 lbs)
Library case      (10 diskettes)        5       2.5 kg (5.6 lbs)
Fiftyfile         (50 diskettes)        1       0.7 kg (1.5 lbs)
Tab dividers for fiftyfile              5       -
Diskette magazine                       5       3.7 kg (8.0 lbs)
10-pack slip case (10 diskettes)       30       7.7 kg (17 lbs)
Fan file 10       (10 diskettes)        1       1.5 kg (3.3 lbs)
Fan file 20       (20 diskettes)        1       2.2 kg (4.8 lbs)

Note:  Diskettes  are not included with these  accessories.  The
quantities  of diskettes listed indicate the maximum  number  of
diskettes each accessory can contain.

Besides   the   accessories,  IBM  provides   convenience   kits
(including  the diskettes) for certain systems and devices.  The
convenience  kits and the following diskettes and  supplies  are
available  through  your  IRD  (Information  Records   Division)
representative.

                                       Sold in
Item                                 multiples of       Weight
---------------------------------    ------------       ------
Diskettes (Note 1)                      10              1.4 kg (3.0 lbs)
Temporary adhesive identification       30 labels       -
  labels (rainbow pack (Note 2)         (one pack)
  or one color pack)
Protective envelopes (replacement)      50              1.1 kg (2.5 lbs)
Shipping carton for thirty
  10-packs (Note 3)                     25              24.9 kg (55 lbs)
Top and bottom pads for above carton    50              10.0 kg (22 lbs)
Shipping carton for twenty
  10-packs (Note 3)                     25              20.9 kg (46 lbs)
Top and bottom pads for above carton    50              7.3 kg (16 lbs)
Shipping carton for ten
  10-packs (Note 3)                     25              9.1 kg (20 lbs)
Top and bottom pads for above carton    50              4.1 kg (9 lbs)
Shipping carton for five
  10-packs (Note 3)                     25              6.4 kg (14 lbs)
Top and bottom pads for above carton    50              1.8 kg (4 lbs)
Shipping carton for one
  10-pack (Note 3)                      25              4.5 kg (10 lbs)
Shipping carton for one diskette        25              3.2 kg (7 lbs)
Die-cut spacer for a 10-pack (Note 3)   25              2.5 kg (5.5 lbs)
Zip-top plastic bags                    10              -

Notes:
1:  Diskettes  are  shipped in boxes of  10;  each  diskette  is
enclosed in a protective envelope. Each box also contains a pack
of temporary adhesive labels.
2:  A  rainbow pack contains 30 labels, six each of  red,  blue,
yellow, green and gray.
3:  10-pack  is  a shortened title for  the  10-pack  slip  case
included in the accessory list.


APPENDIX A. DISKETTE USERS
--------------------------

The  following  list of diskette using systems  and  devices  is
divided  by  diskette  types. Some of the  systems  and  devices
appear in more than one place in the list because they use  more
than  one  type  of diskette. The list is  current  as  of  this
edition date and will be updated. Note, however, that new  using
systems  and  devices may become available between  editions  or
revisions to this manual.


IBM diskette 1
--------------

128 bytes per sector

IBM 3540 diskette input/output unit
IBM 3601 finance communication controller, models 1, 2A, 2B, 3A, and 3B
IBM 3602 finance communication controller
IBM 3741 data station
IBM 3742 dual data station
IBM 3747 data converter
IBM 3773 communication terminal
IBM 3774 communication terminal
IBM 3775 communication terminal
IBM 3776 communication terminal
IBM 3777 communication terminal
IBM 3791 controller
IBM 3881 optical mark reader, model 3
IBM 3890 document processor
IBM 4331 processor
IBM 4962 disk storage unit, models 2, 2F, and 4
IBM 4964 diskette unit
IBM 4966 diskette magazine unit
IBM 5114 diskette unit
IBM 5231 controller, model 2
IBM 5265 point of sale terminal, all models
IBM 5320 system unit -- System/32
IBM 5340 system unit -- System/34, all models
IBM 5381 system unit -- System/38
IBM 7840 film thickness analyzer
IBM 7841 textile color analyzer
IBM 7842 coating analyzer
IBM 8101 storage and input/output unit
IBM 8130 processor
IBM 8140 processor


256 bytes per sector

IBM 3601 finance communication controller, models 1, 2A, 3A, and 3B
IBM 3602 finance communication controller
IBM 3631 plant communication controller, models 1A and 1B
IBM 3632 plant communication controller, models 1A and 1B
IBM 3791 controller
IBM 4962 disk storage unit, models 2, 2F, and 4
IBM 4964 diskette unit
IBM 4966 diskette magazine unit
IBM 5114 diskette unit
IBM 5381 system unit -- System/38
IBM 8101 storage and input/output unit
IBM 8130 processor
IBM 8140 processor


512 bytes per sector

IBM 4962 disk storage unit, models 2, 2F, and 4
IBM 4964 diskette unit
IBM 4966 diskette magazine unit
IBM 5114 diskette unit
IBM 5320 system unit -- System/32
IBM 5340 system unit -- System/34, all models
IBM 5381 system unit -- System/38
IBM 7840 film thickness analyzer
IBM 7841 textile color analyzer
IBM 7842 coating analyzer


IBM diskette 2
--------------

128 bytes per sector

IBM 4962 disk storage unit, models 2, 2F, and 4
IBM 4964 diskette unit
IBM 4966 diskette magazine unit
IBM 5114 diskette unit
IBM 5381 system unit -- System/38


256 bytes per sector

IBM 3601 finance communication controller, models 2B and 3B
IBM 3602 finance communication controller, models 1A and 1B
IBM 3631 plant communication controller, model 1B
IBM 3632 plant communication controller, models 1A and 1B
IBM 4962 disk storage unit, models 2, 2F, and 4
IBM 4964 diskette unit
IBM 4966 diskette magazine unit
IBM 5114 diskette unit
IBM 5381 system unit -- System/38


IBM diskette 2D
---------------

256 bytes per sector

IBM 4966 diskette magazine unit
IBM 5114 diskette unit
IBM 5265 point of sale terminal, models X3X and X4X
IBM 5340 system unit -- System/34, models X2X and X3X
IBM 5381 system unit -- System/38
IBM 8101 storage and input/output unit
IBM 8130 processor
IBM 8140 processor


512 bytes per sector

IBM 4966 diskette magazine unit
IBM 5114 diskette unit
IBM 5381 system unit -- System/38


1024 bytes per sector

IBM 4966 diskette magazine unit
IBM 5114 diskette unit
IBM 5340 system unit -- System/34, models X2X and X3X
IBM 5381 system unit -- System/38


APPENDIX B. DATA ORGANIZATION
-----------------------------

Physical and logical records
----------------------------

A  record  is  a collection of related items of  data  that  are
treated as a unit. You may be able to improve the efficiency  of
your  diskette  operations by varying the way you  organize  the
records  on  your diskettes. The two choices discussed  in  this
appendix  and  shown in the examples are  physical  records  and
logical records.

The sector defines the maximum length of a physical record.  The
lengths are fixed for each type of diskette. These lengths  are:
128, 256, 512, and 1024 bytes (see "IBM diskette types", earlier
in  this manual). If, however, you choose not to  restrict  your
information  to the fixed lengths of the physical  records,  you
may organize your information into logical records.

A  logical  record is independent of  its  physical  environment
because it is not defined in physical terms, but rather in terms
of  the  information it contains.  Therefore,  the  relationship
between logical and physical records varies. One example of data
organization may have logical records divided into portions that
occupy  one or more physical records. Another example  may  have
several logical records occupying one physical record.


Blocking and spanning
---------------------

A block is a set of adjacent logical records that is recorded as
a unit. For basic data exchange and type H exchange, you can set
a block to any value greater than zero, but not greater than the
physical  record  length.  For  other  types  of  diskette  data
organization, the relationship of the block size to the physical
record size can be governed by the constraints of the system.

The  following paragraph uses illustrations to help clarify  the
explanations  of  blocking  and  spanning.  In  each  of   these
illustrations, the terms record and physical record appear.  The
records shown on the top lines of the illustrations are  logical
records.

You  can place records on the diskette as blocked or  unblocked,
spanned or unspanned, or in combinations of these four  options,
for example:

Blocked: One record plus one or more records (or a segment of  a
record)  occupy  a  single block.  The  following  examples  are
illustrations  of three possible combinations that form  blocked
records:

+- Record -+--- Record ---+--- Record ---+-- Record --+  +- Record -+----
           | Seg   Segment| Segment   Seg|                          | Seg
           +----+  +------+--------------+                          +----
==== Block =====   ==== Block =====   ==== Block =====   ==== Block =====
--- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---


+- Rec -+- Rec -+  +- Rec -+- Rec -+  +- Rec -+- Rec -+  +- Rec -+- Rec -+
==== Block =====   ==== Block =====   ==== Block =====   ==== Block =====
--- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---


+- Record -+- Record -+- Record -+    +- Record -+- Record -+- Record -+
============= Block =============     ============= Block =============
--- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---


Unblocked:  One record exclusively occupies one or more  blocks.
The  following  examples  are illustrations  of  three  possible
combinations that form unblocked records:

+--- Record ---+   +--- Record ---+   +--- Record ---+   +--- Record ---+
==== Block =====   ==== Block =====   ==== Block =====   ==== Block =====
--- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---


+- Record -+       +- Record -+       +- Record -+       +- Record -+
==== Block =====   ==== Block =====   ==== Block =====   ==== Block =====
--- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---


+------------- Record ------------+   +------------- Record ------------+
==== Block =====   ==== Block =====   ==== Block =====   ==== Block =====
--- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---


Spanned:  One  record extends beyond one  block.  The  following
examples  are  illustrations of two possible  combinations  that
form spanned records:

+------------- Record ------------+   +------------- Record ------------+
==== Block =====   ==== Block =====   ==== Block =====   ==== Block =====
--- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---


+- Record -+--- Record ---+--- Record ---+-- Record --+  +- Record -+----
           | Seg   Segment| Segment   Seg|                          | Seg
           +----+  +------+--------------+                          +----
==== Block =====   ==== Block =====   ==== Block =====   ==== Block =====
--- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---


Unspanned:  One or more records do not extend beyond one  block.
The  following  examples  are illustrations  of  three  possible
combinations that form unspanned records:

+--- Record ---+   +--- Record ---+   +--- Record ---+   +--- Record ---+
==== Block =====   ==== Block =====   ==== Block =====   ==== Block =====
--- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---


+- Record -+       +- Record -+       +- Record -+       +- Record -+
==== Block =====   ==== Block =====   ==== Block =====   ==== Block =====
--- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---


+- Rec -+- Rec -+  +- Rec -+- Rec -+  +- Rec -+- Rec -+  +- Rec -+- Rec -+
==== Block =====   ==== Block =====   ==== Block =====   ==== Block =====
--- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---


Blocked  and  Spanned:  The following  example  illustrates  the
combining of blocked and spanned records:

+- Record -+--- Record ---+--- Record ---+-- Record --+  +- Record -+----
           | Seg   Segment| Segment   Seg|                          | Seg
           +----+  +------+--------------+                          +----
==== Block =====   ==== Block =====   ==== Block =====   ==== Block =====
--- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---


Blocked  and  Unspanned: The following examples  illustrate  the
combining of blocked and unspanned records:

+- Rec -+- Rec -+  +- Rec -+- Rec -+  +- Rec -+- Rec -+  +- Rec -+- Rec -+
==== Block =====   ==== Block =====   ==== Block =====   ==== Block =====
--- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---


+- Record -+- Record -+- Record -+    +- Record -+- Record -+- Record -+
============= Block =============     ============= Block =============
--- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---


Unblocked  and  Spanned: The following example  illustrates  the
combining of unblocked and spanned records:

+------------- Record ------------+   +------------- Record ------------+
==== Block =====   ==== Block =====   ==== Block =====   ==== Block =====
--- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---


Unblocked  and Unspanned: The following examples illustrate  the
combination of unblocked and unspanned records:

+--- Record ---+   +--- Record ---+   +--- Record ---+   +--- Record ---+
==== Block =====   ==== Block =====   ==== Block =====   ==== Block =====
--- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---


+- Record -+       +- Record -+       +- Record -+       +- Record -+
==== Block =====   ==== Block =====   ==== Block =====   ==== Block =====
--- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---


+--------- Record ---------+          +--------- Record ---------+
============= Block =============     ============= Block =============
--- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---   --- Phys Rec ---



Sequential data
---------------

Sequential  data  organization provides a way in which  you  can
organize  each of the diskette types. In the  descriptions  that
follow,  the expression logical sequence means that the  sectors
are read or written in sequence numerically; that is 1, 2, 3, 4,
and so on. For ease of illustration, these examples show reading
or  writing  beginning  at  track or  cylinder  1;  however,  in
practice, reading or writing can begin at any track or cylinder.

Because the organization for the IBM diskette 2 is identical  to
that for the IBM diskette 2D, only one description is given.


The IBM diskette 1: A one-sided diskette that requires only  one
read/write  head.  Reading  or  writing  sequentially  on   this
diskette proceeds as follows:

     1. Start  at track (cylinder) 1; in logical sequence,  read
        or write each sector of the track.

     2. Move to track (cylinder) 2; in logical sequence, read or
        write each sector of the track.

     3. Move to track (cylinder) 3; in logical sequence, read or
        write each sector of the track.

     4. Continue in this manner to the EOD.


The  IBM  diskettes 2 and 2D: Two-sided diskettes  that  require
read/write heads on each side. The diskette drive switches  from
read/write  head 0 to read/write head 1 electronically.  Reading
or writing sequentially on this diskette proceeds as follows:

     1. Start  at cylinder 1 with read/write head 0; in  logical
        sequence, read or write each sector of the track.

     2. Still  on  cylinder  1, switch to  head  1;  in  logical
        sequence, read or write each sector of the track.

     3. Move  to cylinder 2, switch back to head 0;  in  logical
        sequence, read or write each sector of the track.

     4. Still  on  cylinder  2, switch to  head  1;  in  logical
        sequence, read or write each sector of the track.

     5. Move  to cylinder 3, switch back to head 0;  in  logical
        sequence, read or write each sector of the track.

     6. Still  on  cylinder  3, switch to  head  1;  in  logical
        sequence, read or write each sector of the track.

     7. Continue in this manner, switching from one side of  the
        diskette to the other... to the EOD.


APPENDIX C. INITIALIZATION AND TRACK FORMAT
-------------------------------------------

Initialization
--------------

Initialization is a part of the process of preparing a  diskette
for shipment to the purchaser. Each new diskette is  initialized
following  a careful inspection, to ensure that it  contains  no
manufacturing  defects that could prevent accurate  writing  and
reading.  Initialization writes the label information  and  data
addresses  on the diskette recording surface. The  formats  used
for the index cylinder and the data set labels are discussed  in
Appendix D and Appendix E.

Reinitialization

Some IBM systems have facilities to reinitialize diskettes. This
process  permits  you  to change the size of the  sectors  on  a
diskette,  or to bypass a maximum of two defective cylinders  or
tracks.  Note that, unless your system has a  special  provision
for  saving the information contained on the diskette,  all  the
information is lost during reinitialization.

In  this  process,  the system flags  a  defective  cylinder  by
filling all of the ID fields on that cylinder with binary  ones.
The  system then writes the cylinder number from  the  defective
cylinder  into the ID field of the next physical cylinder.  This
means  that the ID from every cylinder whose  physical  cylinder
number  is higher in value than the defective cylinder is  moved
up to the next respective cylinder.

The  physical  cylinder  numbers  of  defective  cylinders   are
recorded  in  the error map sector (sector 05 of side 0  of  the
index cylinder). When the device encounters a defective cylinder
during   read   or  write  operations,   the   read/write   head
automatically moves to the next physical cylinder.


Track format
------------

Except  for the index cylinder, each track on a new diskette  is
initialized to the same basic format. The information in some of
the  sectors varies with the diskette type. For more details  on
the  contents of the index cylinder and cylinders 1 through  76,
see Appendix D and Appendix E.

The following illustration shows how the tracks are formatted at
initialization. Also shown on the illustration are numbers  that
serve as keys to the notes that describe the particular fields.

        :        :      :          :
      +-+--------+      +----------+
     /  |  Last  |      |   Last   |
    /   | sector |      |  sector  |
   /+---+--------+------+----------+
  //    |  Gap   |      | Preindex |
 //     |        |      |   Gap    |
O--Index+========+      +==========+<-- Index detected
 \\     |  Gap   |   |Postindex gap|
  \\    +--------+------+----------+-+--> ID field of Sector 01
   \\   | Sector |      |   Sync   | |
    \\  |   01   |      |  field   | | (Note 1 below)
     \+-+--------+      +----------+ |
      \ | Sector |\     |   AM1    | | Hex FE (identifies ID field)
       \|   02   | \    +----------+ |
        +--------+  +   | Cylinder | | (see details below)
        | Sector |  |   |  number  | |
        |   03   |  |   +----------+ |
        +--------+  |   |   Head   | | (see below)
        :        :  |   |  number  | |
                    |   +----------+ |
                    |   |  Record  | | (see below)
                    |   |  number  | |
                    |   +----------+ |
                    |   | Physical | | (see below)
                    |   |  record  | |
                    |   |  length  | |
                    |   +----------+ |
                    |   |   CRC    | | (Note 2)
                    |   +----------+-+
                    |   | Post-ID  |
                    |   |   Gap    |
                    |   +----------+-+--> Data field of Sector 01
                    |   |   Sync   | |
                    |   |  field   | |
                    |   +----------+ |
                    |   |   AM2    | | (Note 3)
                    |   +----------+ |
                    |   | Number of| |
                    |   |  bytes   | | (Note 4)
                    |   +----------+ |
                    +   |   CRC    | |
                     \  +----------+-+
                      \ | Postdata |
                       \|   gap    |
                        +----------+-+--> ID field of Sector 02
                        |   Sync   | |
                        |  field   | |
                        +----------+ |
                        |   AM1    | |
                        +----------+ |
                        | ID field | | (Note 5)
                        :          : :

where

Cylinder number:
hex 00 through hex 4A (decimal 0 through 74; cylinders 75 and 76
are used as alternative cylinders).

Head number:
hex  00  for  one-sided  diskettes  and  side  0  for  two-sided
diskettes;
hex 01 for side 1 of two-sided diskettes.

Record number:
Hex 01 through hex 1A for 128-bytes-per-sector format diskette 1
Hex 01 through hex 1A for 128-bytes-per-sector format diskette 2
Hex 01 through hex 1A for 256-bytes-per-sector format diskette 2D
Hex 01 through hex 0F for 256-bytes-per-sector format diskette 1
Hex 01 through hex 0F for 256-bytes-per-sector format diskette 2
Hex 01 through hex 0F for 512-bytes-per-sector format diskette 2D
Hex 01 through hex 08 for 512-bytes-per-sector format diskette 1
Hex 01 through hex 08 for 1,024-bytes-per-sector format diskette 2D

Physical record length:
Hex 00 for 128-bytes-per-sector format
Hex 01 for 256-bytes-per-sector format
Hex 02 for 512-bytes-per-sector format
Hex 03 for 1,024-bytes-per-sector format


Note 1:
Binary zero sync bytes

Note 2:
Cyclic redundancy check. The check bytes are generated during  a
write  operation,  and  are  used during  both  write  and  read
operations to verify that the data is correct.

Note 3:
Various  systems  have  the ability to  modify  records  or  the
locations of records. These modifications are as follows:

      - Logically delete a record

      - Move  a  record  from a defective  sector  to  the  next
        sequential sector

      - Move a record from a defective sector to an  alternative
        sector

These  modifications  are made by changing the contents  of  the
address  marker  AM2 and the first character of the  data  field
that  immediately follows AM2. When the first character  of  the
data  field changes, the data field changes to a  control  field
that designates what type of modification was made.

Note: The address marker AM2 usually contains a hex FB. When any
of  the three modifications is necessary, AM2 is changed to  hex
F8. F8 alerts the device to check the first character of the
next field.

Note 4:
128; 256; 512; or 1,024 bytes.
The  value  of the first character of this field  specifies  the
type   of  modification  that  has  affected  the  record   that
previously  occupied the sector. The characters used  and  their
significance are:

      - D, which means delete the record. During subsequent read
        operations, the device ignores the remaining contents of
        this sector.

      - F,  which means move the record to the  next  sequential
        sector.  During subsequent read operations,  the  device
        ignores  the  remaining  contents of  this  sector,  and
        searches for the record in the next sequential sector.

      - . (period), which means move the record to a sector that
        has been allocated as an alternative sector. The address
        of  the  alternative  sector is  written  in  the  error
        directory  (sector 05 on side 0 of the index  cylinder).
        During subsequent read operations, the device reads  the
        period, and searches for the sector address in the error
        directory (error map).

Note 5:
The  ID  field contains the sync field, address  marker  1,  the
address  and  length  of the record, and  CRC  bits.  From  this
information,  the system can identify and locate the record.  If
the  cylinder is defective, all the ID fields on  that  cylinder
are filled with binary ones.


APPENDIX D. INDEX CYLINDER LAYOUT
---------------------------------

Every new IBM diskette is inspected and initiated. The following
table  lists  the  sectors  of  the  index  cylinder,  the  byte
positions within the sectors, the purposes for those  positions,
and the values written in the byte positions. Occasionally,  you
will  find a number in parentheses in the Initialized to:  line.
These numbers represent the various diskette types:

(128-1) = a one-sided diskette with 128-bytes per sector

(256-1) = a one-sided diskette with 256-bytes per sector

(512-1) = a one-sided diskette with 512-bytes per sector

(128-2) = a two-sided diskette with 128-bytes per sector

(256-2) = a two-sided diskette with 256-bytes per sector

(256-2D) = a two-sided, double-density diskette with 256-bytes per sector

(512-2D) = a two-sided, double-density diskette with 512-bytes per sector

(1024-2D) = a two-sided, double-density diskette with 1024-bytes per sector

Where  there  is  a  difference  in  the  value  written  for  a
particular  diskette type, the Initialized to: line  shows  both
the  number  that  represents the diskette type  and  the  value
assigned  to that diskette type. The following example from  the
Initialized  to:  line  shows  that the value  for  two  of  the
diskette  types  differs from the value assigned  to  the  other
diskette types. The values are shown in hexadecimal:

(128-1) = Hex 40

(256-1) = Hex C2

(512-1) = Hex 40

(128-2) = Hex 40

(256-2) = Hex C2

(256-2D) = Hex 40

(512-2D) = Hex 40

(1024-2D) = Hex 40


The index cylinder on a new IBM diskette

Format: Side
        Sector
        Positions and use
        Initialized to:

Side: 0
Sector: 01
Positions and use: Positions 1-80 are reserved for IPL and IMPL.
Initialized to: Hex 40

Side: 0
Sector: 01
Positions and use: Positions 81-128 are reserved for IPL and IMPL.
Initialized to: Hex 00

0
02
Positions 1-80 are reserved for IPL and IMPL.
Hex 40

0
02
Positions 81-128 are reserved for IPL and IMPL.
Hex 00

0
03
Positions 1-80 are reserved for system scratch.
Hex 40

0
03
Positions 81-128 are reserved for system scratch.
Hex 00

0
04
Positions 1-80 are reserved.
Hex 40

0
04
Positions 81-128 are reserved.
Hex 00

0
05
Positions  1-5 = ERMAP. (ERMAP is a label that  identifies  this
record as an error map.)
ERMAP

0
05
Position 6 is a separator, and contains a blank.
Hex 40

0
05
Positions 7-8 contain blanks if no defective cylinders exist. If
defective  cylinders exist, positions 7-8 contain the number  of
the first defective physical cylinder.
Hex 40

0
05
Position 9 is a blank if no defective cylinder exists. If one or
more defective cylinders exist, position 9 contains a zero.
Hex 40

0
05
Position 10 is a separator, and contains a blank.
Hex 40

0
05
Positions  11-12 contain blanks if one or no defective  cylinder
exists.  If more than one defective cylinder  exists,  positions
11-12  contain  the  number of  the  second  defective  physical
cylinder.
Hex 40

0
05
Position  13 is a blank if one or no defective cylinder  exists.
If more than one defective cylinder exists, position 13 contains
a zero.
Hex 40

0
05
Position 14 is a separator, and contains a blank.
Hex 40

0
05
Positions 15-22 are reserved.
Hex 40

0
05
Position  23  is the defective record indicator. It  contains  a
blank to indicate that no defective records to be handled by the
alternative physical record method are contained within the data
portion of any data set extent on the volume. At least one  such
defective record exists if position 23 contains a D.
Hex 40

0
05
Position  24  is the error directory indicator.  It  contains  a
blank to indicate that no format or alternative physical  record
relocation  has been previously specified. B or C indicates  the
defective physical records have had their contents relocated  to
a  data  set named ERRORSET. B indicates the  addresses  of  the
defective  physical  records  have been recorded  in  the  error
directory in the discontinuous binary format (OCHR). C indicates
that  the addresses of the defective physical records have  been
recorded in the error directory in the character decimal  format
(bCCHRR).
(128-1) = Hex 40
(256-1) = Hex C2
(512-1) = Hex 40
(128-2) = Hex 40
(256-2) = Hex C2
(256-2D) = Hex 40
(512-2D) = Hex 40
(1024-2D) = Hex 40

0
05
Positions 25-72 are the error directory. This directory contains
entries of addresses of physical records containing one or  more
defects.  In the discontinuous binary format (0CHR), this  field
can contain addresses of up to 12 relocated physical records. In
the  character decimal format (bCCHRR), this field  can  contain
the address of up to 8 relocated physical records. The relocated
records  are contained in a data set named ERRORSET in the  same
sequence as the addresses in the directory. Unused positions  of
the  error  directory must contain binary zeros if  position  24
contains  a B. If position 24 contains a C, unused  portions  of
the error directory must contain blanks.
(128-1) = Hex 40
(256-1) = Hex 00
(512-1) = Hex 40
(128-2) = Hex 40
(256-2) = Hex 00
(256-2D) = Hex 40
(512-2D) = Hex 40
(1024-2D) = Hex 40

0
05
Positions 73-80 are reserved.
Hex 40

0
05
Positions 81-128 are padded.
(128-1) = Hex 00
(256-1) = Hex 00
(512-1) = Hex 00
(128-2) = Hex 00
(256-2) = Hex 00
(256-2D) = Hex 40
(512-2D) = Hex 40
(1024-2D) = Hex 40

0
06
Positions 1-80 are reserved.
Hex 40

0
06
Positions 81-128 are reserved.
Hex 00

0
07
This  sector is called the volume label. Various fields in  this
sector identify the diskette: the owner, security, sequence, and
length of physical records.
Positions 1-4 identify the sector as a volume label.
VOL1

0
07
Positions 5-10 are called the volume identifier. This field  can
contain  the  same  volume identifier (serial  number)  that  is
written on the diskette permanent label. The ID consists of  one
to  six  digits  or  letters. The first  character  must  be  in
position 5 of the sector, and any unused positions in the  field
to  the  right  of the ID data must be  blanks.  No  blanks  are
allowed  between  digits  or letters in  this  field.  When  the
diskette  is  initialized  by an IBM  device,  this  field  will
contain  the  value  specified as  part  of  the  initialization
procedure.
IBMIRD

0
07
Position  11 is the volume accessibility field. A blank in  this
field permits access to the diskette. Any nonblank character  in
this  field  means additional qualifications  are  required  for
further access.
Hex 40

0
07
Positions 12-37 are reserved.
Hex 40

0
07
Positions  38-51  are called the owner  identifier  field.  This
field is not used by some systems.
Hex 40

0
07
Positions 52-64 are reserved.
Hex 40

0
07
Position  65 is the label extension indicator. The character  in
this  position  (space or 1 through 9) indicates the  number  of
cylinders  (in  addition to cylinder 0) that  are  allocated  as
system  area  needed for data set labels. A non-space  value  is
only allowed on the IBM diskette 2D. The indicator values mean:
Space = No additional cylinders allocated
        (all data set labels are on cylinder 0).
    1 = Cylinder 1 is reserved as system area.
    2 = Cylinders 1 and 2 are reserved as system area.
    3 = Cylinders 1, 2, and 3 are reserved as system area.
  4-9 = A  maximum of nine additional cylinders can be  reserved
        as system area.
The  value in position 65 must be entered when the  diskette  is
initialized  and  must  not  be  changed  during  normal   label
processing. Using systems are not required to read or write  the
data sets whose labels are in the extended system area, but  all
systems must be able to detect position 65.
When  the  system does not support label  extension,  allocation
must  be prohibited if position 65 equals any value  other  than
space.  Data  sets  with labels on cylinder 0  can  be  read  or
updated,  as  long  as the data set extents  are  not  modified.
However,  any data sets that have labels in the extended  system
area  are not accessible, and must not be identified as  type  H
exchange.
Hex 40

0
07
Positions 66-71 are reserved.
Hex 40

0
07
Position 72 is the volume surface indicator, and contains either
a blank, a 2, or an M. A blank indicates one recording  surface;
2  indicates  two recording surfaces; M  indicates  two  double-
density recording surfaces.
(128-1) = Hex 40
(256-1) = Hex 40
(512-1) = Hex 40
(128-2) = Hex F2
(256-2) = Hex F2
(256-2D) = Hex D4
(512-2D) = Hex D4
(1024-2D) = Hex D4

0
07
Position 73 is the extent arrangement indicator, and contains  a
blank or a P. A blank indicates there are no special constraints
on  the arrangement of extents, data set labels, or  unallocated
space on this diskette. P indicates the extents must be adjacent
and must begin at cylinder 1, head 0, sector 1. P also indicates
that  the  data  set labels must begin at cylinder  0,  head  0,
sector  8, and must be in the same sequence as the extents  they
describe.  P  also  indicates that all  unallocated  space  must
follow  the  last data set extent on the volume. If  any  unused
space  is created elsewhere, the extents must be  rearranged  to
eliminate the space, or this field must be changed to a blank.
Hex 40

0
07
Position 74 is the special requirements indicator, and  contains
a  blank  or an R. A blank indicates that there are  no  special
requirements for accessing data on this volume. R indicates that
some  of  the  data  sets were  recorded  in  a  logically  non-
sequential manner.
Hex 40

0
07
Position 75 is reserved.
Hex 40

0
07
Position  76  identifies  the  length  of  the  physical  record
(sector) on cylinders 1 through 76, and contains a blank, 1,  2,
or 3:
Blank = 128 bytes
    1 = 256 bytes
    2 = 512 bytes
    3 = 1024 bytes
(128-1) = Hex 40
(256-1) = Hex F1
(512-1) = Hex F2
(128-2) = Hex 40
(256-2) = Hex F1
(256-2D) = Hex F1
(512-2D) = Hex F2
(1024-2D) = Hex F3

0
07
Positions 77-78 are the physical record (sector) sequence  code.
This field contains blanks or the characters 01 through 13,  and
indicates  the  physical  sequence  of sectors.  A  blank  or  1
indicates the sectors are physically sequential. Otherwise, this
field  is  used a an increment to determine  the  next  physical
sector. Diskettes initialized on an IBM device may have a  value
specified as part of the initialization procedure.
Hex 40

0
07
Position 79 is reserved.
Hex 40

0
07
Position  80  is the label standard version field.  W  indicates
that IBM standard labels are on the diskette.
W

0
07
Positions 81-128 are padded.
(128-1) = Hex 00
(256-1) = Hex 00
(512-1) = Hex 00
(128-2) = Hex 00
(256-2) = Hex 00
(256-2D) = Hex 40
(512-2D) = Hex 40
(1024-2D) = Hex 40

Side: 0, Sectors: 08-26  and Side: 1, Sectors: 01-26
These sectors are used to record the data set labels that define
the  data  sets  recorded  on cylinders 01  through  74  of  the
diskette. Sectors 09 through 26 on side 0 and sectors 01 through
26  on side 1 are initialized as deleted records. (See  Appendix
E.)


APPENDIX E. DATA SET LABEL LAYOUT
---------------------------------

Every  new  IBM  diskette  is  inspected  and  initialized.  The
following  table  lists  the  character  positions  and  labels,
descriptions  of  the  labels, and the  values  written  in  the
character  positions.  Occasionally, you will find a  number  in
parentheses  in one or both of the Initialized to:  line.  These
numbers represent the various diskette types:

(128-1) = a one-sided diskette with 128-bytes per sector

(256-1) = a one-sided diskette with 256-bytes per sector

(512-1) = a one-sided diskette with 512-bytes per sector

(128-2) = a two-sided diskette with 128-bytes per sector

(256-2) = a two-sided diskette with 256-bytes per sector

(256-2D) = a two-sided, double-density diskette with 256-bytes per sector

(512-2D) = a two-sided, double-density diskette with 512-bytes per sector

(1024-2D) = a two-sided, double-density diskette with 1024-bytes per sector

Where  there  is  a  difference  in  the  value  written  for  a
particular  diskette type, the Initialized to: lines  show  both
the  number  that  represents the diskette type  and  the  value
assigned  to that diskette type. The following example from  the
Initialized  to:  lines shows that the value for  three  of  the
diskette  types  differs from the value assigned  to  the  other
diskette  types.  The  values  are  shown  in  hexadecimal  (the
character b represents a blank):

(128-1) = DDR1

(256-1) = Dbbb

(512-1) = Dbbb

(128-2) = DDR1

(256-2) = Dbbb

(256-2D) = DDR1

(512-2D) = DDR1

(1024-2D) = DDR1


Data set labels on a new IBM diskette

Format: Character position
        Label
        Description
        Initialized to: Sector 08, Side 0
                        Sectors 09-26, Side 0 and Sectors 01-26, Side 1

Character position: 1-4
Label: Label ID (identifier)
Description: Label identifier for system application
Initialized to:
Sector 08, Side 0: DDR1
Sectors 09-26, Side 0 and Sectors 01-26, Side 1:
(128-1) = DDR1
(256-1) = Dbbb
(512-1) = Dbbb
(128-2) = DDR1
(256-2) = Dbbb
(256-2D) = DDR1
(512-2D) = DDR1
(1024-2D) = DDR1

Character position: 5
Label: (none)
Description: Position 5 is reserved
Initialized to:
Sector 08, Side 0: b
Sectors 09-26, Side 0 and Sectors 01-26, Side 1: b

6-22
Data set identifier
User name for data set. The name must be 1 to 17 characters. The
first  character  must  be alphabetic.  No  blanks  are  allowed
between  characters.  Duplicate names are not permitted  on  the
same diskette. For basic data exchange and type H exchange, only
the  first 8 characters are used. The names  ERRORSET,  SYSAREA,
and ERMAP are reserved for special use.
DATAb...b
(128-1) = DATA09...b through DATA26b...b
(256-1) = b...b
(512-1) = b...b
(128-2) = DATA09b...b through DATA26b...b
(256-2) = b...b
(256-2D) = DATA09b...b through DATA26b...b
       and DATA27b...b through DATA77b...b (**)
(512-2D) = DATA09b...b through DATA26b...b
       and DATA27b...b through DATA77b...b (**)
(1024-2D) = DATA09b...b through DATA26b...b
        and DATA27b...b through DATA77b...b (**)

Note **: These are the odd-numbered bytes (DATA27, 29, 31,  ...,
75,  77); the even-numbered bytes are in positions  134  through
150.

23-37
Block length
This  field contains a numeric value that specifies the  maximum
number of characters per block. At label creation, the  contents
must   be  entered.  Blocks  must  begin  on   physical   record
boundaries. For a basic exchange data set, this field must be 1-
128. For a type H data set, this field must be 1-256.
Sector 08, Side 1:
(128-1) = bb080
(256-1) = 00256
(512-1) = bb512
(128-2) = bb128
(256-2) = 00256
(256-2D) = bb256
(512-2D) = bb512
(1024-2D) = b1024
Sectors 09-26, Side 0 and Sectors 01-26, Side 1:
(128-1) = bb080
(256-1) = bbbbb
(512-1) = bb512
(128-2) = bb128
(256-2) = bbbbb
(256-2D) = bb256
(512-2D) = bb512
(1024-2D) = b1024

28
Record attribute
Indicates  blocking used within the data set. When the  exchange
type indicator (position 44) is a blank or H, this field must be
a blank.
b = Records unblocked, unspanned
R = Records blocked, spanned
B = Records blocked, unspanned
S = Records unblocked, spanned
b
b

29-33
Beginning of extent (BOE)
Identifies  the  address of the first sector of  the  data  set.
Positions  29-30  contain  the  cylinder  number,  position   31
contains the head number, and positions 32-33 contain the sector
number. (Some systems use a logical record number. In this case,
position 74 of the volume label contains an R.)
Sector 08, Side 1: 01001
Sectors 09-26, Side 0 and Sectors 01-26, Side 1:
(128-1) = 74001
(256-1) = bbbbb
(512-1) = 75001
(128-2) = 75001
(256-2) = bbbbb
(256-2D) = 75001
(512-2D) = 75001
(1024-2D) = 75001

34
Physical record length
Indicates physical record length:
b = 128 bytes per record
1 = 256 bytes per record
2 = 512 bytes per record
3 = 1024 bytes per record
The  value in this field must be the same as position 76 of  the
volume label. When the exchange type indicator (position 44)  is
a blank, this field must be a blank. When position 44 is H, this
field must contain a 1.
Sector 08, Side 1:
(128-1) = b
(256-1) = 1
(512-1) = 2
(128-2) = b
(256-2) = 1
(256-2D) = 1
(512-2D) = 2
(1024-2D) = 3
Sectors 09-26, Side 0 and Sectors 01-26, Side 1:
(128-1) = b
(256-1) = b
(512-1) = 2
(128-2) = b
(256-2) = b
(256-2D) = 1
(512-2D) = 2
(1024-2D) = 3

35-39
End of extent (EOE)
Identifies the address of the last sector reserved for this data
set, using the same format as BOE.
Sector 08, Side 0:
(128-1) = 73026
(256-1) = 74015
(512-1) = 74108
(128-2) = 74126
(256-2) = 74115
(256-2D) = 74126
(512-2D) = 74115
(1024-2D) = 74108
Sectors 09-26, Side 0 and Sectors 01-26, Side 1:
(128-1) = 73026
(256-1) = bbbbb
(512-1) = 74108
(128-2) = 74126
(256-2) = bbbbb
(256-2D) = 74126
(512-2D) = 74115
(1024-2D) = 74108

40
Record/block format
This  field  contains a blank or F, and  indicates  fixed-length
records  in  fixed  blocks. When  the  exchange  type  indicator
(position 44) is a blank or H, this field must be blank.
b
b

41
Bypass indicator
Indicates  a  data  set to be skipped during  exchange  or  copy
operations  when transmitting or transferring the data  sets  on
the volume. If this position is set to a blank, the data set  is
transferred; if it is set to B, the data set is not transferred.
b
b

42
Data set security
A blank indicates the data set is not secured (can be accessed).
A non-blank character means restricted access. When the position
is  non-blank, the volume accessibility indicator in the  volume
label (track 00, sector 07) must also be non-blank.
b
b

43
Write protect
If  this data set contains a P, the data set can be  read  only.
This field must be a blank to allow both reading and writing.
b
b

44
Exchange type indicator
A  blank  indicates  the data set can be  used  for  basic  data
exchange;  H indicates the data set is a type H data set.  An  E
indicates  that additional label checking must be  performed  in
order to exchange the data set. (See Appendix F.)
Sector 08, Side 0:
(128-1) = b
(256-1) = E
(512-1) = E
(128-2) = b
(256-2) = E
(256-2D) = H
(512-2D) = E
(1024-2D) = E
Sectors 09-26, Side 0 and Sectors 01-26, Side 1:
(128-1) = b
(256-1) = b
(512-1) = E
(128-2) = b
(256-2) = b
(256-2D) = H
(512-2D) = E
(1024-2D) = E

45
Multivolume indicator
A  blank in this field indicates a data set is wholly  contained
on this diskette; C indicates a data set is continued on another
diskette;  L  indicates the last diskette on which  a  continued
data set resides.
b
b

46-47
Volume sequence number
Specifies the sequence of volumes in a multivolume data set. The
sequence must be consecutive, beginning with 01 (to a maximum of
99). Blanks indicate that volume sequence checking is not to  be
performed  on  this  volume  and all  subsequent  volumes  of  a
multivolume data set.
bb
bb

48-53
Creation date
May  be  used to record the date the data set was  created.  The
format  is  YYMMDD, where YY is the low-order 2  digits  of  the
year,  MM is a 2-digit representation of the month, and DD is  a
2-digit representation of the day of the month. Blanks  indicate
that the creation date is not significant.
bbbbbb
bbbbbb

54-57
Record length
At label creation, record length must be defined. A blank  means
the  record length equals the block length defined  in  position
23. (A blank or H in position 44 also means record length equals
block length; therefore, this field can be ignored.)
bbbb
bbbb

58-62
Offset to next record space
This  field  indicates  the  starting  position  for  the   next
sequential  record relative to the end of the last block  before
EOD  (end of data) and contains blanks or a decimal value to  be
used  as a negative displacement. Blanks mean zero  displacement
from the next block (starts at EOD address). This field is  used
only in conjunction with blocked records.
bbbbb
bbbbb

63-66
(none)
Positions 63-66 are reserved.
bbbb
bbbb

67-72
Expiration date
May be used to contain the date the data set (and its label) may
be  deleted. The format is the same as creation date  (positions
48-53). All blanks indicate the data set is considered  expired.
All 9s indicate the data set will never expire.
bbbbbb
bbbbbb

73
Verify/copy indicator
This  field  must  contain a blank, V, or C.  A  blank  must  be
entered here when the data set is created. Systems that  support
verification  enter  a  V  to indicate the  data  set  has  been
verified.  Systems that support copy verification enter a  C  to
indicate  the data has been successfully transferred to  another
medium (for example, tape, transmission network). Do not enter C
for partial data set copy or for null data set.
b
b

74
Data set organization
This field must contain a blank, S, or D. A blank or S indicates
sequential  data  organization. (See Appendix B.) D  means  some
organization  that  does not permit  the  sequential  relocation
method  of  processing  defective  physical  records.  When  the
exchange  type  indicator (position 44) is a blank  or  H,  this
field must contain a blank.
b
b

75-79
End of data (EOD)
Identifies the address of the next unused sector within the data
set  extent, using the same format as BOE. If this field is  the
same as BOE, the extent contains a null data set. If this  field
contains  the address of the next block beyond the  extent  (for
unblocked, unspanned records), the entire extent has been  used.
For  blocked  or spanned records, this field must be  used  with
offset  to next record space (positions 58-62) to determine  the
end of actual data recorded.
Sector 08, Side 0: 01001
Sectors 09-26, Side 0 and Sectors 01-26, Side 1:
(128-1) = 74001
(256-1) = bbbbb
(512-1) = 75001
(128-2) = 75001
(256-2) = bbbbb
(256-2D) = 75001
(512-2D) = 75001
(1024-2D) = 75001

80
(none)
Position 80 is reserved.
b
b

81-128
Positions 81-128 are padded.
Sector 08, Side 0:
(128-1) = Hex 00
(256-1) = Hex 00
(512-1) = Hex 00
(128-2) = Hex 00
(256-2) = Hex 00
(256-2D) = Hex 40
(512-2D) = Hex 40
(1024-2D) = Hex 40
Sectors 09-26, Side 0 and Sectors 01-26, Side 1:
(128-1) = Hex 00
(256-1) = Hex 00
(512-1) = Hex 00
(128-2) = Hex 00
(256-2) = Hex 00
(256-2D) = Hex 40
(512-2D) = Hex 40
(1024-2D) = Hex 40


The  following  positions  apply  only  to  the   double-density
diskettes (2D), Side 1:

129-132
(none)
Same as positions 1-4.
Sectors 01-26, Side 1:
(256-2D) = DDR1
(512-2D) = DDR1
(1024-2D) = DDR1

133
(none)
Same as position 5.
Sectors 01-26, Side 1: b

134-150
(none)
Same as positions 6-22.
Sectors 01-26, Side 1:
(256-2D) = DATA28b...b through DATA78b...b (**)
(512-2D) = DATA28b...b through DATA78b...b (**)
(1024-2D) = DATA28b...b through DATA78b...b (**)

Note **: These are the even-numbered bytes (DATA28, 30, 32, ...,
76, 78); the odd-numbered bytes are in positions 6 through 22.

151-155
(none)
Same as positions 23-27.
Sectors 01-26, Side 1:
(256-2D) = bb256
(512-2D) = bb512
(1024-2D) = b1024

156
(none)
Same as position 28.
b

157-161
(none)
Same as positions 29-33.
Sectors 01-26, Side 1:
(256-2D) = 75001
(512-2D) = 75001
(1024-2D) = 75001

162
(none)
Same as position 34.
Sectors 01-26, Side 1:
(256-2D) = 1
(512-2D) = 2
(1024-2D) = 3

163-167
(none)
Same as positions 35-39.
Sectors 01-26, Side 1:
(256-2D) = 74126
(512-2D) = 74115
(1024-2D) = 74108

168
(none)
Same as position 40.
b

169
(none)
Same as position 41.
b

170
(none)
Same as position 42.
b

171
(none)
Same as position 43.
b

172
(none)
Same as position 44.
Sectors 01-26, Side 1:
(256-2D) = H
(512-2D) = E
(1024-2D) = E

173
(none)
Same as position 45.
b

174-175
(none)
Same as positions 46-47.
bb

176-181
(none)
Same as positions 48-53.
bbbbbb

182-185
(none)
Same as positions 54-57.
bbbb

186-190
(none)
Same as positions 58-62.
bbbbb

191-194
(none)
Same as positions 63-66.
bbbb

195-200
(none)
Same as position 67-72.
bbbbbb

201
(none)
Same as position 73.
b

202
(none)
Same as position 74.
b

203-207
(none)
Same as positions 75-79.
Sectors 01-26, Side 1:
(256-2D) = 75001
(512-2D) = 75001
(1024-2D) = 75001

208
(none)
Same as position 80.
b

209-256
(none)
Same as positions 81-128.
Sectors 01-26, Side 1:
(256-2D) = Hex 40
(512-2D) = Hex 40
(1024-2D) = Hex 40


APPENDIX F. DATA EXCHANGE
-------------------------

Data exchange is the name given to a process whereby information
is  written  on  a diskette at one system and  used  in  another
system.  To  ensure  that the exchange  of  information  can  be
accomplished  efficiently and without errors,  certain  standard
formats  have  been established. These formats  are  basic  data
exchange, type H data exchange, and type E general exchange.


Basic data exchange
-------------------

Basic  exchange  data  sets  have  requirements  assuring   that
diskettes  may be exchanged between systems capable  of  reading
and writing both the IBM diskette 1 and the IBM diskette 2.

For basic exchange data sets, the exchange type indicator  (data
set label position 44) must be a blank. This means:

      - The data set is organized sequentially.

      - The records are a maximum of 128 bytes long.

      - The records are of fixed length, unblocked, and unspanned.

      - The physical record length is 128 bytes.

      - The  data  set identifier (data set  label  positions  6
        through 22) is not longer than eight positions.

Additional  requirements vary between the IBM diskette 1 and  2.
IBM diskette 1 must:

      - Be   initialized  with  physically  sequential   records
        (Volume  label positions 77 and 78 are specified  either
        bb (blank) or 01.)

      - Have basic exchange data sets on tracks 1 through 73 only.

IBM diskette 2 must:

      - Be   initialized  with  physically  sequential   records
        (Volume  label positions 77 and 78 may be  specified  bb
        (blank) or 01 through 13.)

      - Have basic exchange data sets on cylinders 1 through 74.

No  diskette containing basic exchange data sets is  allowed  to
use alternative physical record relocation.


Type H data exchange
--------------------

Type  H  exchange  data sets  have  requirements  assuring  that
diskettes  may be exchanged between systems capable  of  reading
and writing the IBM diskette 2D.

For type H exchange data sets, the exchange type indicator (data
set label position 44) must be an H. This means:

      - The data set is organized sequentially.

      - The records are a maximum of 256 bytes long.

      - The records are of fixed length, unblocked, and unspanned.

      - The physical record length is 256 bytes.

      - The  data  set identifier (data set  label  positions  6
        through 22) is not longer than eight positions.

In addition, a diskette containing type H exchange data sets may
be  initialized with physically non-sequential  records  (volume
label positions 77 and 78 are space or 01 through 13).

In  a  type  H exchange data set,  alternative  physical  record
relocation is not allowed.


Type E general exchange
-----------------------

Type E exchange data sets have requirements that force the using
system to examine each field in the header label. None of  these
fields can be assumed or summarized.

For type E exchange data sets, the exchange type indicator (data
set label position 44) must be an E. This means:

      - On output, all supported fields must contain values that
        accurately  describe the data set, and  all  unsupported
        fields must contain space characters.

      - On  input,  all  supported fields  must  be  checked  to
        accurately determine the attributes of the data set.


APPENDIX G. GLOSSARY
--------------------

address:
The  location of any physical record on the diskette,  specified
by  the  cylinder number, head number, and  record  number.  (In
publications describing the locations of a physical record on  a
one-sided  diskette,  the address might be  specified  by  track
number, 00, and record number.)

AM:
Address marker.

basic data exchange:
A  format  for exchanging data on diskettes between  systems  or
devices that use the IBM diskettes 1 and 2.

block
A set of adjacent logical records recorded as a unit.

blocking:
Combining two or more records into one block.

BOE:
Beginning of extent

byte:
A sequence of adjacent binary digits operated on as a unit;  the
representation of one character.

C:
Celsius.

cm:
Centimeters.

cyclic redundancy check:
A method of error checking performed when reading or writing data.

cylinder:
The  tracks  that  can be  accessed  without  repositioning  the
read/write heads.

data set:
The  major unit of data storage, consisting of a  collection  of
data records stored in a user-specified format.

diskette drive:
The  portion of the system or device that handles  the  diskette
functions.

diskette envelope:
The  removable,  protective envelope in which  the  diskette  is
stored.

diskette jacket:
The permanent, protective cover that houses the flexible disk.

diskette magazine:
A  container  for  up  to 10 diskettes;  used  on  the  diskette
magazine drive.

diskette magazine drive:
A  diskette  drive  that automatically  loads  and  unloads  the
diskettes from a diskette magazine.

double density:
Bits written on the IBM diskette 2D at twice the density used on
IBM diskettes 1 and 2.

drive spindle:
The  portion  of  the diskette drive that  is  inserted  in  the
diskette and revolves, turning the disk within the jacket.

EOD:
End of data.

EOE:
End of extent.

F:
Fahrenheit.

head:
See read/write head.

ID:
Identification.

IMPL:
Initial MicroProgram Load.

index cylinder:
Cylinder  00. This cylinder is used to store  information  about
the diskette.

index hole:
The small hole in the disk and the jacket; used for timing.

initialization:
The   process   of  writing  the   addresses,   index   cylinder
information,  and  other  system information  on  the  diskette.
(Initialization is also used to assign alternative cylinders.)

IPL:
Initial Program Load.

IRD:
Information Records Division.

kg:
Kilograms.

logical record:
A record that does not necessarily conform to the boundaries  of
a  physical  record. The logical record can be longer  than  the
physical  record,  shorter than the physical record, or  one  of
several logical records within a single physical record.

permanent diskette label:
The  label attached permanently to the upper left corner of  the
diskette jacket.

Physical record:
One or more records written within one sector on a track.

read (operation):
The  process  of  sensing the magnetic fields  on  the  diskette
recording  surface and converting them into signals  appropriate
for use by the system or device.

read/write head:
The unit in the diskette drive that reads from or writes on  the
diskette recording surface.

record:
A collection of related items of data, treated as a unit.

recording surface:
The portion of the diskette that is used to store information.

sector:
The addressable unit into which each track is divided.

spanned record:
A logical record stored in more than one block.

temporary identification label:
The  removable label attached to the upper right corner  of  the
diskette jacket.

track:
That portion of the diskette recording surface available to  one
read/write head at each access position.

type E general exchange:
A  method  for exchanging unformatted data  on  diskettes.  This
exchange requires the using system to examine the header labels.

type H data exchange:
A  format  for exchanging data on diskettes between  systems  or
devices that use the IBM diskette 2D.

unblocked:
One logical record that exclusively occupies one or more blocks.

unspanned:
One or more logical records that do not extend beyond one block.

write (operation):
The  process  of  generating magnetic  fields  on  the  diskette
recording surface.


INDEX
-----

(To be done by WS4...)


EOF