Archived from groups: alt.comp.periphs.mainboard.asus (
More info?)
In article <XfSdnRUOEsY-XvLfRVn-sw@comcast.com>, "jime"
<jimeiffe@comcast.net> wrote:
> I am building a P4P800-E Deluxe. I will O/C it.
> Do I have to use the best quality memory (most expensive) 1GB about $250
> vs other at $150?
>
> Thanks,
> Jim
875P/865PE - available ratios between CPU/MEM 1:1, 5:4, 3:2
If overclocking by 25%:
P4C800-E Stable using any ratio
P4P800-E Stable at 5:4 ratio, but not 1:1 (see this thread...)
http://www.abxzone.com/forums/showthread.php?t=62275&highlight=artifact+p4p800
Examples:
P4 2.8GHz overclock to 3.5GHz
2.8GHz at CPU clock 200MHz, becomes 3.5GHz at CPU clock 250MHz.
At 250MHz, 1:1 ratio is 250MHz memory clock or DDR500 memory.
At 250MHz, 5:4 ratio is 200MHz memory clock or DDR400 memory.
If you buy P4P800-E and plan on 25% overclock, then the safe bet is
5:4 ratio. Some PC3200 memory should suffice.
If you buy P4C800-E and plan on 25% overclock, then either 1:1 or
5:4 ratios are possible. At 1:1, some DDR500 (PC4000) memory can
be used. At 5:4, some DDR400 (PC3200) memory can be used.
If you buy PC4000 memory, thinking it can support anything, well,
yes it can, but most overclockers try to optimize CAS and speed
at the same time. Finding a memory with a low CAS and a speed that
matches their planned overclock, gives the best possible performance.
In terms of performance, this Tomshardware article compared
how much effect CAS has on performance. It doesn't look like
much, and it really depends on how crazy you are about getting
the last percentage point, as to whether it is worth it or not.
http://www.tomshardware.com/motherboard/20040119/index-09.html#application_benchmarks
If you buy PC4000 RAM, it can be run at rates slower than PC4000.
When it comes to performance, there are a couple of aspects to
it. To a first order approximation, "Clock Rate is King". What
this means, is the first priority is to lift the CPU core clock
rate, and don't worry about the memory performance. That means,
for example, you can buy ordinary PC3200 memory, run the processor
at 2.8GHz 1:1, or when overclocking, 3.5Ghz 5:4, using the same
PC3200 memory at its stock speed of DDR400 in both cases.
A secondary effect, is memory bandwidth. Optimizing memory bandwidth
will help with Photoshop, 3D rendering, video applications, anything
that pumps a lot of bits through the memory bus. A 10% improvement
in memory bandwidth, speeds up the application by 3%. You can see that
it is easier to squeeze out performance, by simply increasing the
CPU core clock first. It is harder to squeeze out even more
performance, by using premium memory.
So, you can buy practically any memory from PC3200 to PC4000 at
CAS3, and have some fun with it. With the P4P800-E, you could
buy some PC4000 memory, experiment with 1:1 ratio (and see if
there are any artifacts), or eventually settle on 5:4 ratio,
running the memory at PC3200. If you buy PC3200 memory, then
you are stuck at 5:4 ratio when overclocking (or 3:2 ratio if
you overclock even higher).
Buying a memory with enhanced CAS, is handy if you move the
memory between machines, and some of the machines are more
demanding than others. For example, I have some PC3200 CAS2
Ballistix that I can bounce between a P4C800-E and a A7N8X-E
without problems. The CAS2 is handy for keeping cranky
motherboards like the A7N8X-E happy at DDR400.
Lower CAS memory can be used if you like impressive benchmarks,
but is only a worthwhile imvestment if
1) You make a living from the computer. If you Photoshop for a
living, then optimize CAS. Pay the extra money. Buy WD
Raptors for your scratch disks.
2) You do nothing but memory intensive applications. Low CAS
is working for you all the time.
If this is just a "surf computer", CAS3 is good enough.
For professional overclockers, memory selection is a time
consuming task, because you have to consider all the
conditions you might use, in terms of clock choices,
voltages, and so on. There are some amazing memories out
there, at amazing prices. For example, using a DIMM
voltage booster to increase memory voltage above the stock
2.6V voltage, this product can be run at DDR500 with CAS2
memory timing - these are extreme conditions, and might not
be too good for the motherboard. This is the memory you
use, if trying to set some kind of world record for 3DMark,
or SuperPI calculation times:
http://www.ocztechnology.com/products/memory/ocz_el_ddr_pc_4000_gold_vx
HTH,
Paul
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