Quick summary: 32M 2K refresh SIMMs without mod.
128M 4K referesh SIMMs with mod.
The details:
The largest memory that will work without the modification is 32M.
16M and 32M SIMMs must be 2K refresh else you will only see 1/2 the
memory.
This is because there are 11 address lines wired in the Webpal.
That gives you 2K x 2K = 4M words. Since the memory is
32 bits wide, thats 16M bytes. There are two RAS pins for two banks
(so called double-sided SIMMs), so that gives you the top value of 32M.
If you get a 4K refresh SIMM, then that means that the arrays are 4K by
something. Thus, you'll see 1/2 the total memory size. This usually
only affects 16M and 32M SIMMs.
If you make the mod to wire up another address pin to the SIMM socket then
you can use those 4K 64M and 128M SIMMs since you can now support
a 4K by 4K arrays giving 16M words or 64K bytes. Again, with the two RAS
pins for a so-called double sided SIMM, the max is 128M.
In theory, one can wire up a second SIMM socket using the remaining
two RAS pins and support twice as much memory as above, but that would
be a pretty major task!
Bill
