History said:
Thanks for the responses. I was prompted to ask because I asked the
same question in a Dell online forum and got this response:
<<The Rank number is the number of 48 bit memory areas on the module. It
does NOT refer to single or double sided modules. Rank 1 has a single data
path to the chip, so it's always active. With Rank 2, the memory controller
may need to switch from one path to the other, thus possibly slowing down
accesses. Usually only important with some machines, such as a server with a
limited number of paths.>>
The above response may be describing some kind of registered
module behavior. Your motherboard uses unbuffered DIMMs.
See section 10.2.2.1 of page 228. This is the 945G datasheet.
http://download.intel.com/design/chipsets/datashts/30750203.pdf
It would appear the "dual channel interleaved" has a relaxed
requirement. For dual channel, they only want the total
quantity of memory in each channel to be the same. That
implies a degree of independence between the channels, unlike
previous chipsets where logically one address/control structure
drove the two partnered DIMMs in a matched pair. Taking a quick
flip through the document, there doesn't seem to be as much
complexity of modes, as in some previous DDR Northbridge designs.
In terms of memory dimensions, rows, columns, and banks, are the
three dimensions inside a memory chip. The memory chip has a
certain data width at its interface, like x4, x8, or x16 bits
wide. Memory chips are formed into groups of 64 bits wide, to
match the interface on the DIMM. If the DIMM used x8 chips,
then 8 chips would form a "rank". If x16 chips were used, then
only 4 chips would be needed to form a rank. An unbuffered DIMM
has a maximum of two ranks per DIMM, and the physical arrangement
frequently would be double sided for that. (That is because the
wiring pattern would be nasty if both ranks were put on the same
side of the DIMM.) For DDR memory, there is one ugly product, which
is a 1GB DIMM with 16 chips of x4 wide each, which is a double
sided DIMM yet is only a single rank. I haven't heard of any
DDR2 unbuffered DIMMs constructed that way, so maybe with DDR2
you are more likely to find "double sided" = "two ranks".
On some previous chipsets, Intel offered a "memory guide" document,
which described how to get the best performance from the chipset,
when selecting memory. No doc seems to be available for the
945G.
This is the last memory guide I'm aware of, from Intel. This is
for the 925X. The description in here seems to be consistent with
what I see in the datasheet for the 945G. For some reason,
the text in the figures here is messed up, and I guess Intel
never noticed. So it doesn't look like there are many restrictions
on the memory, not like earlier chipsets. I think you can
relax.
http://download.intel.com/design/chipsets/applnots/30234403.pdf
Paul
