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- Which RAM to get PC2700, 333MHzDDR...
November 24, 2006, 2:25 am
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For memory, it says:
"184-pin DIMM Sockets for unbuffered DDR 400 / 333 SDRAM up to 2 G"
My CPU is CeleronD 3.2 GHz, 533 FSB.
Does 533FSB equate to the 333MHZ DDR ( and a P4 with 400 MHz FSB uses
400 MHZ DDR) ?
So any I looking for 333MHz DDR or PC3200 or PC2700...
Howdoes PC2700 or PC3200 relate to FSB?
Re: Which RAM to get PC2700, 333MHzDDR...
No, your FSB is quad-pumped, meaning 4 x 133MHz = 533
Therefore, DDR memory would be 2 x 133 = 266
That's more commonly known as PC2100.
However, most of those boards (not certain about yours-
check your bios settings and/or manual) will allow an
asynchronous memory bus speed that is +33 MHz faster, so
instead of 133MHz memory clock rate ( * 2 ) , it'd be
running at 166MHz * 2.
Basically this means you could run PC2100 memory if you
wanted to, but CeleronD is pretty hungry for memory
bandwidth so it'd likely a slight performance increase to go
with the PC2700.
Even though the PC2700 is suggested above, PC3200 is
backwards compatible and is probably the best choice (since
there is little to no difference in cost), as it'll merely
provide more margin of stability.
The other performance oriented choice is the memory timings.
Preferribly CAS2.5 not CAS3, or even CAS2 (,2,2,5) if you
wanted to pay a premium for highest performance possible,
though it's no guarantee that's the set of timings your
board would use, especially if you're adding new memory
along with existing memory rated for slower (higher
In short, the generic most cost:performance beneficial
answer is to get PC3200 CAS2.5 spec'd to use no more than
2.6V (default, though they'll tolerate a bit more if
Take PC(nnnn)... divide (nnnn) by 8.
3200 / 8 = 400. That's DDR, so divided by 2 for DDR
400 / 2 = 200 (MHz clock rate).
Thus, if you want or need to run a synchronous memory bus to
FSB speed, 200MHz memory bus clock = 200MHz FSB clock.
200MHz FSB clock on a P4 with quad pumped bus is * 4
4 * 200 = 800 ... as-in, the 800 in "P4MSD-800".
In the case of PC2700, dividing by 8 <> 333, rather 338, but
the 2700 term is merely rounded up for esthetic marketing
Re: Which RAM to get PC2700, 333MHzDDR...
The value you get from the memory choice, depends on what
options are available in the BIOS. The worst (generic)
style BIOS, have no BIOS page at all for the memory
interface. The BIOS simply sets the timing and frequency
as it sees fit. A better designed BIOS, will allow the user
to manually set the speed.
Since the Machspeed downloadable manual doesn't document the
BIOS, there is no way to guess at how fully functional the
BIOS is. This is a purchase criterion for me - if the downloadable
manual doesn't show the BIOS screens, don't buy it. Otherwise,
be satisfied with whatever performance config the BIOS applies
to your hardware.
In a competing product, with a P4M800 chipset, the memory can
be programmed to run at DDR266, DDR333, or DDR400.
I expect the chipset on that motherboard is single channel.
(But the following chart doesn't state that explicitly.)
If the processor is FSB533, the processor transfers at
533MHz x 8 bytes = 4264MB/sec. A PC3200 memory transfers
at 3200MB/sec. To feed that example processor, from a single
channel memory, you want to keep the memory going as fast as
possible. So the DDR400 setting in the BIOS would be desirable.
(When the processor transfer rate is faster than the memory,
the processor has to wait a bit, for the read data.)
If the processor used was FSB400, that is 400MHz x 8 bytes per
transfer, or 3200MB/sec. Which is balanced by a single channel
DIMM at PC3200 speed. Again, you want the memory to run at
least at PC3200. And since memory is not 100$ efficient (not
transferring on every cycle), clocking the memory faster than
the DDR400 rate, actually helps.
Use the highest setting offered, and use PC3200 RAM. CAS3 is
the cheapest memory, and lower CAS number gives slight better
performance. But probably not enough to justify the price
difference. (Also, if the BIOS doesn't take advantage of the
CAS performance offered, it wouldn't make much sense either, but
without documentation in the manual, you don't know what to
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