P4-specific SDRAM?

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This is old stuff but I'm curious. I always used AMD in the
Pentium 4 days and didn't pay much attention when I saw some
SDRAMs being advertised as being for P4s. I happened to see it
again today in a price list, one item being marked (PIV) among
other 133 MHz SDRAMs. Can anybody please elaborate?

Re: P4-specific SDRAM?

pawihte wrote:
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It's more fun with a question like this, if you include a URL.

A Pentium 4 uses a chipset to interface to RAM. So it is the
characteristics of the chipset that would be of interest.

In the RAM business, there are a few cases where terms like
"high density/low density" are used to describe RAM. For example,
with PC133, there are 256MB high density (8 chips of 32Mx8) and 256MB
low density (16 chips of 16Mx8) modules. Some older chipsets
will only half address the high density ones. The chips used, have
a different setup for rows * columns of the matrix. And
that is what causes the problem. (It could have been
solved, if the chipset designers had realized these
eight chip modules would happen. But the standards only
go so far, in defining what to expect.)

There are SDRAM chipsets, that can handle larger modules,
meaning more row/column bits. I think my 845 based P4 board
can do that (Asus P4B). I have 3x512MB in it right now. I think
it can even take 1GB PC133 modules. (The 845 chipset exists
in SDRAM and DDR designs, and mine is an SDRAM design.)

In DDR memory, when the modules are 1GB in size, there are
high density and low density modules there as well. The
number of chips may be 16 in each case. One module may use
(16) 64Mx8 and that would be low density. The other would
use (16) 128Mx4 chips. The first module contains two ranks
of memory. The second (high density) one contains one rank.
Some chipsets don't have sufficient address bits, to handle
the rows * columns used at 128M. For example, Nforce2 can
only half address the 128Mx4 chip. Since the high density
modules are mostly sold on Ebay, it is easiest to just say
"don't buy 1GB DDR modules on Ebay". Branded RAM makers won't
sell high density modules, so the modules in question won't
have a name like Corsair/Crucial/Kingston/OCZ/Geil etc.
The Ebay vendors may call them "Samsung", but that is
referring to the chips, as if the module is also made
by Samsung. Chances are, the module is made by some
small job shop in China. They fling around "Samsung" in
the advert, to make it appear legitimate. (To me, the
best RAM, is the RAM that works in any computer, not
restricted to a limited group of chipsets.)

As far as I know, there is no "leakage" of server chips
(x4) into desktop applications, with DDR2 and DDR3. So
at present, no need to be more wary of Ebay sellers, if
DDR2 or DDR3 modules are offered. Just the usual
quality concerns.

There is nothing wrong with x4 wide chips. They belong on
things like registered ECC or FBDIMM modules. They don't
belong on desktops (if you check Intel desktop chipset
datasheets, x4 are always excluded from their memory type
list - they show x8 or x16 chips instead as the ones they


Re: P4-specific SDRAM?

Paul wrote:
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I saw the PIV spec from a price list I downloaded. I live in a
small town in India, and though I don't buy from them I d/l their
price list from time to time for use as a reference. Sort of a
personal pricewatch.com. I just checked their website and they
don't mention the PIV spec except on the downloadable price list.
The URLs are -
Home: http://www.computerwarehousepricelist.com
Price list:

Thanks a lot for the detailed explanation. I'm an electronics
tech, mostly analog, and have a limited knowledge of digital and
computer technology. But I can understand the concept of address
bit width, matrices and module density after reading your patient
explanation. My approach used to be that if a mobo/chipset is
specced to be able/unable to use double-sided RAM sticks, I took
that at face value. At least I knew that single-sided and
double-sided do not have to literally mean the physical mounting
of chips on one or both sides of the RAM pcb.

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