Searcher7 said:
I understand you can use DDR400 on a motherboard that takes DDR266,
but how would one know if the DDR400 modules in those links you posted
are DDR, DDR2, or DDR3?
I wouldn't need a ruler, because anything smaller than 1-1/4" in
height would fit. I know that because that is the height of the ram
module that I have to wedge up under the DVD case.
Thanks.
Darren Harris
Staten Island, New York.
You generally can tell from naming convention
PC3200 DDR400 184-pin UDIMM (U stands for unbuffered, rather than R for registered)
PC2-3200 DDR2-400 240-pin UDIMM # This is DDR2
PC3-3200 DDR3-400 240-pin UDIMM # This is DDR3 - keying slot is in a different location
# You can't jam a DDR3 in a DDR2 slot, because of the key.
I made up those values so they'd all be the same as far as speed
goes, so the "2" and "3" used would stand out more. DDR has
no number, while DDR2 has the 2 in the parameter, and
DDR3 has the 3 in the parameter.
The memory industry has a relatively poor record when it
comes to marketing RAM, and in some cases, JEDEC gave them
descriptors they could use, and they didn't bother using
them in advertising material.
One practice I find abhorrent, is putting pictures of the
wrong memory product, in an advertisement. Like putting a
picture of unbuffered RAM in a registered RAM advert. You
can assign zero trust to any picture in a RAM advert (don't
use the picture as a deciding factor). Even Ebay sellers
have a better record, than retailers. Ebay sellers are more
likely to use a picture of the actual product (even if
the picture was taken with their cellphone).
*******
If we take this advert
http://www.memoryten.com/pc/018911/DDR-184p-PC3200-1GB/
"1GB 184p PC3200 CL3 16c 64x8 DDR400 2Rx8 2.5V UDIMM 25mm Board Low profile,
Samsung/3rd, ACZ, GR1GU1"
The PC3200 is DDR type.
The DDR400 is DDR type. A DDR400 can be used at DDR400, DDR333, DDR266, or DDR200 speed.
The CL3 means CAS3 (industry standard speed, while CAS2 is "enthusiast speed" or "low latency")
Column Address Strobe latency, affects how long it takes to get the first read data.
16c means 16 chips per module, 8 chips on each side (establishes number of bits inside chip).
This is important for working out whether the number of row or column
address bits are about to be exceeded. If a module uses 16 chips, then
you can use the "max capacity per slot" claimed by the chipset, without
thinking about it. If the module has 8 chips or 4 chips total, then you
have to think carefully about the impact that would have. An 8 chip 512MB
module would probably work OK. A 4 chip 256MB module would probably work
OK. You can assume, when the chipset manufacturer says "1GB max", they're
referring to a 16 chip module (two ranks of 8 chips per side). The module
on the MP3CAR site, was double sided four chip for eight chips total, while the
module capacity was 512MB, which in fact would be right up to the limit
of your motherboard. The 16 chip module, means one fewer row/column bit
is going to be needed to address the memory matrix (number of chips is double,
density can be cut in half, one fewer address bit at that density).
64x8 refers to the internal chip dimensions. Each memory chip is 64 million
locations by 8 bits wide. That makes each chip "512 megabit technology".
If we multiply 16c * 64MB per chip, we get confirmation of the 1GB module size.
2Rx8 means "two ranks" of memory. We'd expect the module to be double-sided.
There are a few other fields in that string, that I can't decode (ACZ, GR1GU1).
Retailers are fond of adding perfectly useless dimensional information
to DIMM adverts. Some of these are constructed to be ambiguous, and
cannot be used to determine whether to buy the module or not. The
marketing people only add that crap, to "plump up the advert".
In some cases, precision is needed, for those chipsets with known
marginal conditions. An example was "440BX high density versus
low density RAM". Each generation has some obscure thing like that,
that occasionally affects people. Even weirder, is when a chipset
maker, doesn't actually know the correct max RAM capacity of what
they've built (VIA Technologies)
My VIA based motherboard
will take a 2GB module, when their web site says "1GB max per slot".
And at least one VIA web page, changed the story over time (like,
had an original claim that one of their chipsets could handle 16GB
total, when it was highly unlikely to do so - this was later
corrected). If VIA had posted datasheets for download, less
erroneous info might have resulted (engineers are closer to
the writing of datasheets, and have next to no say in what is
printed in web pages).
Have fun,
Paul
