The 630 has one 72-pin SIMM slot that can take anything up to a (single banked) 64MB SIMM and reputedly can even work with some 128MB SIMMs (very rare). Your best bet is to find a 72 pin 32MB SIMM as most of those seem to work fine.

Click to expand...

The 631 and 640 actually have two RAM slots. The second one can only use single-sided SIMMs (one bank only, I suppose). I don't know what the max capacity is.

All 630, 635, 636, 637, and 638 boards are otherwise identical, and they should all have the empty pads for the second RAM slot. A person accustomed to soldering could possibly install the second slot all by himself.

Peace,

Drew