AMD751 Northbridge datasheet - page 66 covers the memory controller.
http://cdrom.amd.com/21860/21910.pdf
In the table on page 66, the third from the bottom row of the
table, is the key to making 128MB and 256MB unbuffered modules.
(The row above it, would allow a 512MB module to be constructed,
but it would have 32 chips, and would fry the memory controller,
and as an unbuffered module, such a design is not viable.)
8-Bit Wide Device (Four Banks x 4 Mbits) = 16Mbit x 8
8 devices
128 Mbytes total
Bank address bits = 2//MA12-13
Rows = 12 address bits
Columns = 10 address bits
Here is an example of the right kind of memory chip. In the
column labelled "16Mx8", you can see it has 12 row bits and
10 column bits.
http://download.micron.com/pdf/datasheets/dram/sdram/128MSDRAM.pdf
Here is a properly constructed 256MB DIMM for K7M. Found via
the
www.kingston.com search engine for RAM for motherboards.
Uses (16) 16Mx8 chips for 256MB. Would use (8) 16Mx8 chips
if it was only a single sided 128MB module. In other words,
to make a 256MB module that works, it has to be double sided.
A 128MB module can be single sided, if the chips are 16Mx8 chips.
(As I understand it, the reason Kingston dispenses PC100 for
this application, is there is some kind of timing difference
between the chips. At least I think that is why they do that.
I don't think it has to do with the logical dimensions of the
chips.)
http://www.valueram.com/datasheets/KVR100X64C2_256.pdf
I realize this doesn't help you too much, except to note that
if you looked up information about the memory chips (by using the
numbers and letters on the chips), you could get enough info
to determine whether the modules are addressable by that
Northbridge.
This is typically referred to, in postings to this group,
as the difference between "high density" and "low density"
RAM. If you look up info on the chips, then you have a
better chance of understanding whether the right chips are
on the modules or not.
HTH,
Paul
