aether said:
There's slots 1 & 2, which are paired with the same type and brand of
memory. (dual channel twin pack) If I were to add two additional DIMMs,
also twin dual channel modules, but of a different brand, would this
cause any problems? Is it preferable that all four slots be of the same
brand and make? Or, just that 1 & 2 and 3 & 4 both be dual channel twin
DIMMs?
Example: for slots 1 & 2 I install -
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=994989&Tab=2&NoMapp=0
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=669365&CatId=1352
Well, seeing as one of your example RAMs is registered and the other
unbuffered, they aren't particularly a good pair of examples.
I'll make up an artificial example
channel 1 channel 2
slot1A [DDR333 CAS2 512MB 8 chips] [DDR333 CAS2 512MB 8 chips] slot2A
slot1B [DDR400 CAS3 512MB 16 chips] [DDR400 CAS3 512MB 16 chips] slot2B
The DIMMs sitting "across from one another", have to match in terms
of rows, columns, banks, and ranks. I could not, for example, use
an 8 chip in 1A and a 16 chip in 2A, because one is single sided
(one rank) and the other is double sided (two ranks). Internally,
the rows and columns on those chips would not match either.
The config shown in the diagram above, would run in dual channel
mode. The BIOS has to select the slower of the operating speed
characteristics, to decide what settings to use. It could, for
example, use DDR333 rate, to avoid exceeding the settings of
the first set of sticks. (It would select DDR333, if you set
the BIOS to [By SPD]. )
If you enter the BIOS and do manual settings, you could try
overclocking the memory, and run the whole thing at DDR400 CAS3,
as the DDR333 CAS2 has a fast enough CAS spec, to handle DDR400
CAS3 rate. Bumping up Trcd by one more than its spec'ed value, might
be enough to squeeze DDR400 from all the memory.
So, if you buy two pairs of RAM, sit them across from one another
so 1A=2A and 1B=2B. As long as one pair is not a gross mismatch
for the application (like using a pair of PC2100 and a pair of
PC3700), it should work OK. If you did use (2) PC2100 and (2) PC3700,
you'd have to run them at PC2100.
It is not essential for all four DIMMs to be the same brand and model
number. But there can be an advantage. If all four DIMMs have matching
rows, columns, banks, and ranks, then the BIOS can set them up to
interleave (use dynamic addressing), which will maximize the open banks
on the DIMMs. That will squeeze a few more percent memory bandwidth
from them, which will make no measurable difference to your applications.
So, this config is faster than the one above, by a few percent,
assuming the same speed and CAS settings are used in both cases.
channel 1 channel 2
slot1A [DDR333 CAS2 512MB 16 chips] [DDR333 CAS2 512MB 16 chips] slot2A
slot1B [DDR400 CAS3 512MB 16 chips] [DDR400 CAS3 512MB 16 chips] slot2B
Paul
