VW wrote:
> Also, generally 32/64MB is the biggest stick supported for the smaller
> stuff, save the 128MB and higher for the towers.
This is not consistently accurate as it turns out.
I sat down with a bunch of SIMMs (32 MB, 64 MB and 128 MB) and an
assortment of power supplies and logic boards (Q605, Q610, Q650,
Q840A, PM6100, PM7100, PM8100) a few years ago. Unfortunately, I did
not have a power supply for the Q630 board I have.
Forget all the stuff people spout about single sided vs. double
sided. All of these machines support double-banked SIMMs. 32 MB
SIMMs are always double sided (two banks of 16 MB built with 4M X 4
chips) and 32 MB SIMMs work in all of the machines. So clearly double
banked SIMMs are supported in all machines.
The thing that limits compatibility is the addressing scheme of the
memory chips. Memory chip addresses are divided into row and column
addresses. So the 22 bits needed to address 4M addresses is divided
into 11 row bits and 11 column bits. 16M addresses needs 24 bits,
which translates to 12 row bits and 12 column bits. The rare 8M X 4
memory chip needed 23 address bits, which is 11 X 12 or 12 X 11 row
and column bits respectively (the former is 2K refresh, the latter is
4K refresh).
Some of the machines do not support a 12th bit of address or only
support it in the row or in the column, and this limts the machine's
ability to address more than 32 MB on a 72 pin SIMM.
Ah, here are my notes. If you do much experimentation with old stuff,
I hghly recommend getting an old fashioned lab notebook to write and
keep notes in...
The Centris/Quadra 610/650/800 addresses 32 MB SIMMs fine. Sixty-
four MB SIMMs are seens as 32 MB. One hundred twenty-eight MB SIMMs
are seen as 64 MB.
The Quadra/LC/Performa 605/475/476 will address 32 MB, 64 MB and 128
MB SIMMs. I have also used a SIMM doubler to successfully install two
128 MB SIMMs in this model, but then you can't close the lid...
The Quadra 840AV addresses 32 MB SIMMs properly. Sixty-four MB SIMMs
are seen as 16 MB. One hundred twenty-eight MB SIMMs are seen as 32
MB.
The PM 7100 and 8100 (and probably 9100) have the same memory
addressing scheme as the Q840AV. This limitation results because
these machines will only address 11 X 11 in the row and column
addresses. This is especially apparent when considering the 128 MB
SIMM results. A 128 MB SIMM is treated just like a 32 MB SIMM. Only
16 MB of each bank is addressed. A 64 MB SIMM appears as if it is a
single bank made of 4m X 4 (11 X 11) chips instead of 16M X 4 (12 X
12) chips.
The Quadra/Centris 610/650 apparently will address 11 X 12 or maybe 12
X 11 chips. It's odd that they do not support 12 X 12, but when they
were made I think there were some 8M X 4 chips in production which
used 11 X 12 addressing.
The PM6100 will address 32 MB, 64 MB and 128 MB SIMMs with the caveat
that it seems to wire the four RAS lines into a different set of two
pairs than is commonly done. The 128 MB SIMMs I used (HP D4893) which
work fine in the Q605, do not work at all in the 6100. I traced the
problem to the fact that the D4893 SIMM wires the four RAS lines
together into pairs in one configuration and the 6100 expects the
opposite configuration. This is probably correctable by moving
resistors on the 128 MB SIMM.
The 64 MB SIMMs I used were HP D4290 DIMMs. These are built out of
eight Samsung 16M X 4 memory chips. 8 X 4 = 32 bits wide (which 72
pin SIMMs are) so the SIMMs are 16M X 32 bits = 16M X 4 bytes = 64
MB. This is a single banked SIMM. All the memory chips share the
same RAS wires.
The 128 MB SIMMs I used were the HP D4893, which are made from 16 16M
X 4 Samsung memory chips. These are just like two of the 4290s on
the same SIMM: two banks. They create two banks by splitting the
four RAS signals on the SIMM between the two sets (banks) of memory
chips. Then the computer activates whichever pair of RAS signals it
needs to in order to address the bank that it needs.
So 32 MB SIMMs are two banks of 4M X 4 chips. 2 X (8 X (4m X 4)) =
2 X (4m X 32 bits) = 2 (16 MB) = 32 MB.
64 MB SIMMs are one bank of 16M X 4 chips (although there are some
monstrosities made of 32 4M X 4 chips). 1 X (8 X (16M X 4)) = 1 X
(16M X 32 bits) = 1 X (64 MB) = 64 MB
128 MB SIMMs are two banks of 16M X 4 chips. 2 X (8 X (16M X 4)) = 2
X (16M X 32 bits) = 2 X (64 MB) = 128 MB.
The only 16M X 4 chips I have seen are the Samsung KM44C16100AK-6 ('A'
may be 'B' or 'C')
The 4M X 4 chips can be from a variety of manufacturers. Examples
are: KM41C16000BK-6, HM5116100S6, TC5116100CSJ-60, HY5116100BJ-60.
Note that the letter after the '6000' or 6100' portion of the part
number is usually a revision number and may vary without affecting the
identity of the part in question.
Jeff Walther
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