Usually the mobo will accept DDR400 memory even if only spec'd for DDR333,
only it will run that DDR400 @ DDR333 (or 166MHz clock). IOW, your mobo
will simply run at the lesser of the memory installed. Same holds true for
CAS. Although before the additional memory you are running at CAS 2.5, the
installation of CAS3 will typically still work, but ALL your memory will run
at the lesser of the CAS ratings, in this case, CAS3.
All DDR (as opposed to DDR2) runs at the same voltage, so this is not an
issue.
And yes, your total memory will be 256mb + 512mb = 768mb
But let me throw another twist into the drama. I checked your mobo spec's @
Gigabyte (
http://www.gigabyte.com.tw/Motherboard/Products/Products_GA-8IR2003 (Rev 2.0).htm )
, and frankly, your current stick of DDR333 is already "over spec'd" for
this mobo. IOW, your mobo is already running @ DDR266 (perhaps only DDR200
is configured for synchronous operation). Adding even higer spec'd memory @
DDR400 is simply wasting money (assuming DDR200/DDR266 can be had for less
than DDR400).
Your mobo only supports a CPU FSB of 400MHz (or 100MHz clock), while your
memory subsystem can handle DDR200/DDR266 (or 100/133MHz clock). That means
you only have the following configuration options:
Option #1:
CPU = 400MHz (100MHz clock, quad-pumped)
MEM = 200MHz DDR (100MHz clock)
Option #2:
CPU = 400MHz (100MHz clock, quad-pumped)
MEM = 266MHz DDR (or 133MHz clock)
Option #1 is "synchronous" since the FSB and memory are running at the same
*clock* speed, which usually means overall better performance compared to
asynchronous operations, even if the memory in an asynchronous configuration
runs a little faster! Option #2 is asynchronous, since the FSB and memory
are NOT running at the same "clock" speed.
IOW, if you have a CPU 400MHz installed, and running w/ DDR333 memory, its
only running DDR266 at best, and possibly only DDR200 (again, depending on
how you have the BIOS configured). And ironically, running @ DDR200 would
probably produce better performance because of the synchronous behavior.
So now you make the situation even worse by adding DDR400, which just like
the DDR333, will only run DDR266 or DDR200. You're simply throwing money
down the drain.
What I suggest is DUMPING your current 256mb DDR33 on eBay, and buy either 2
x 256mb (or 2 x 512mb) of DDR200 (or DDR266 if you think you might like to
continue w/ your current asynchronous configuration). But in most cases,
DDR200 will probably show better performance due to the benefits of
synchronization. Whether DDR200 or DDR266, at least these are a better
match to your mobo, and there's no sense wasting money on the more expensive
memory. Also, by using a matched pair, you can usually take advantage of
other BIOS feature, like bank interleaving. And don't discount the
advantage of running CAS 2.5 vs. 3.0.
Just some suggestions. While you can continue to pursue your original
approach, I'd like to see you get back on track. You'll same some money and
get better performance in the long run.
Jim
