gufus said:
The first one is $73.99 on the Crucial site. And you don't have
to use PayPal to pay for it. The RAM is PC3200 CAS3. You never know,
you might even be able to do better than that price, if you shop
around. Ebay doesn't always have the best prices.
http://www.crucial.com/store/partspecs.aspx?IMODULE=CT2KIT12864Z40B
The second one is a single stick at 1GB. Kingston provides nice PDF
datasheets (which on occasion, they've been known to violate, but
for DDR memory, this should still be accurate). This one is PC3200
CAS3 as well.
http://www.valueram.com/datasheets/KVR400X64C3A_1G.pdf
There are only a few motherboards, that go to insane lengths
when doing matching checks. Some early S939 motherboards did that
(tending to "ignore" the second set of DIMMs), but that was fixed
by a BIOS update.
Regular motherboards, the BIOS selects the lowest common denominator.
If one DIMM was CAS2 and the other CAS3, then the BIOS would select CAS3
(as the fast DIMM can be run slower with no problem). Same with
mixing DDR400 with DDR333, they'd end up at DDR333. And when you run
four DIMMS, the BIOS can also do load compensation - even if you bought
DDR400 DIMMs, the BIOS might still use DDR333 as a setting, due to the
level of bus loading present. In such cases, you have to raise the clock
manually yourself, and test. They select the DDR333 setting, to guarantee
the RAM will run right. But you as the user, can tune for slightly
better performance yourself.
When the DIMMs have different rows, columns, banks, ranks (logical dimensions),
that can affect whether dual channel or some flavor of single channel
mode is used, or even some mixture of the two might result.
The motherboard always runs in that case, but the memory bandwidth
might suffer a little bit. For example, if you buy two single 1GB DIMMs,
one had eight chips (all on one side), the other has sixteen chips (
eight per side, double sided), those modules don't match in logical
dimension. Chipsets like Intel with Flex Memory, don't care, as they
run each DIMM independent when it comes to logical dimension. Some
other motherboards, they run two DIMMs as if they were a 128 bit wide
"super-DIMM", and in that case, a failure to match logical dimension
results in the pair of DIMMs being ignored (or perhaps run in virtual
single channel mode, and accessed 64 bits at a time).
In summary, with respect to the previous paragraph, how it works
is a function of your chipset or processor type. Early S939 for example,
could ignore a mismatched pair of DIMMs. Later, Rev.E processors or higher,
had the option of running single channel modes where the motherboard
would work no matter how badly you bungled the memory purchases.
Considering you could buy the Crucial kit for $73.99, while the Kingston is
$65 for a single stick, I would think for another nine bucks, you could
buy two Crucial kits, and install completely matched RAM (4x1GB). Then
the DIMM already in the computer, can be stored in a drawer for a rainy day.
You don't have to immediately sell it off.
So for the most part, you can mix RAM any way you want and the motherboard
is likely to still boot. But the choices you make, can affect the
performance a bit (not so you'd notice - you need a stopwatch to
detect the difference).
Paul
