On Tue, 02 Oct 2007 17:31:38 -0400, Igor
wrote:

I'm planning to add some memory to a PC. The motherboard supports "DDR up
to 333 MHz (enhanced) memory bus."

333 MHz (PC2700) or slower DDR SDRAM isn't easy to find on today's market,
and when you do find it, it's considerably more expensive than the DDR
which runs at 400 MHz (PC3200). What would happen if I bought 400 MHz DDR
RAM and installed it in a motherboard which only supports speeds up to 333
MHz (PC2700)? Would it work? If it did work, would it work as well as the
slower PC2700 RAM?

Yes it'll work and do so as well/fast as PC2700, providing
it has timings spec'd at least as (Low) fast as the PC2700
module had. This is not a large difference in performance
though so a random suggestion would be to get a CAS2.5 @ 2.5
or 2.6V spec'd part.



I've gotten conflicting answers to this question. Two computer stores told
me that it wouldn't work. Another store and a book I consulted said it
would.

Avoid those two computer stores from now on when seeking
advice, or at least the particular techs you spoke with as
PC3200 is always backwards compatible. It's the same memory
only the maxium speed the PC3200 is guaranteed to be able to
run stabily is higher, and the prom on the module is
programmed with timings to validate this if/when a
motherboard checks to see what the memory can do.



I'd also like some opinions on which brand of RAM I should get. Kingston
and Samsung are ubiquitous where I live, so the choice comes down to one
of those. Both brands are about the same price, with the Samsung being
marginally cheaper.

Which country do you reside in? Often buying online is
cheaper unless there's a particularly good sale or rebate
ongoing. Kingston's valueram tends to be lower spec, many
other name brand modules are better or cheaper for the same
specifications.



Finally, would a 128 MB stick of 266 MHz DDR RAM be able to run in the
same computer as, say, a 512 MB stick of 400 MHz DDR RAM? If so, would
using both at the same time degrade the performance of the faster RAM?

The two could run in single channel mode, which would be the
mode it was in currently. Some motherboard chipsets can run
dual channel mode for a performance increase (which varies
from very little to a fair amount) and some of these require
two of same size and compatible timings, modules. Some only
require two modules with compatible timings but need not be
the same size (would then support dual channel mode only up
to the amount of memory of the smallest module total on one
channel, times 2). nForce 2 is an example of such a chipset
that can do this, though unless using integrated video the
performance gain from dual channel mode is minimal.