|Note 1||A modification is possible so that 640K of RAM can be fitted on the 64-256KB motherboard.
You will need certain parts, and soldering skill. The procedure can be found here.
Be sure to keep track of what you do, so that if things do not work out, you can undo what you have done.
If you are successful, consider marking the motherboard in some way to remind yourself (and others) that the motherboard has been modified.