Minus Zero Degrees IBM XT memory mod.

[Moogle!]

This article talks about adding 640K to an older XT motherboard. It says you add the 32KB chips to bank 0 and 1. My questions is whether or not I will get 1MB if I also put 32KB chips in banks 2 and 3. (along with the appropriate UMB driver)

 

[Chuck(G)]

No, you'll get 640K. There was a thread some time ago that I participated in that involved replacing a bipolar PROM on the motherboard to get another 64K in the upper memory (Dxxx, Exxx) segments. For that, we used a 22V10 GAL.

 

[Stone]

This mod describes a slightly different technique that only requires soldering a jumper between two easily accessible jumper pad contacts:

http://www.textfiles.com/computers/xt-640k.upd

Here's the 1 MB mod:

http://www.vcfed.org/forum/showthread.php?28128-HIMEMV2-or-equivillent-PROM