Mixing Memory?

Hi everyone. I bought an Asus P4P8X motherboard years ago and only
bought 512 MB of PC3200 RAM at the time (my gig of older DDR266 doesn't
work with 800 MHz FSB processors.) I recently saw a deal on PC3200 and
bought another 512 MB.

My old RAM is Corsair Value Select CL3 DDR400 and the new RAM is Ultra
CL3 DDR400. So, both have the same clock speed and both have a latency
of 3 cycles. However, when I start the computer with both installed,
it defaults to 266 MHz!!! Does the RAM need to be installed into
certain slots to get it to run at 400 MHz or are my DIMMs just
incompatible?

-Brandon R.

Brandon wrote:
> Hi everyone. I bought an Asus P4P8X motherboard years ago and only
> bought 512 MB of PC3200 RAM at the time (my gig of older DDR266 doesn't
> work with 800 MHz FSB processors.) I recently saw a deal on PC3200 and
> bought another 512 MB.
>
> My old RAM is Corsair Value Select CL3 DDR400 and the new RAM is Ultra
> CL3 DDR400. So, both have the same clock speed and both have a latency
> of 3 cycles. However, when I start the computer with both installed,
> it defaults to 266 MHz!!! Does the RAM need to be installed into
> certain slots to get it to run at 400 MHz or are my DIMMs just
> incompatible?
>
> -Brandon R.

Dear Brandon,

Here is a link to the P4P8X manual at Asus:

http://dlsvr03.asus.com/pub/ASUS/mb/...1299_p4p8x.pdf

Memory info is on pages 24-26 of the PDF file, pages 1-14 to 1-16 in the
manual's numbering system.

Looks like that motherboard takes PC2700/2100, i.e. 333 and 266 RAM.

It says that "DDR 400 is not a default configuration".

The FSB for this chipset is listed as 533/400--

http://www.anandtech.com/cpuchipsets...spx?i=1823&p=3

***quote***
The cheapest member of the 865 family is the 865P, selling for $33 (the
ICH5-R adds another $3 to all chipset costs) in 1K quantities. The 865P
only supports DDR266 and 333, thus is best suited for 400/533MHz FSB
CPUs; a lack of DDR400 memory support ends up working out just fine
since the chipset doesn't support the 800MHz FSB.

You can consider the 865P to be all of the 865 chipsets that wouldn't
pass Intel's validation at 800MHz FSB and/or 400MHz memory clock. Users
that won't be using an 800MHz FSB CPU and don't plan on upgrading to one
anytime soon will find the 865P the best offering. You may be able to
find 865P motherboards that overclock to support the 800MHz FSB with
Dual DDR400 memory, however there are no guarantees.
***

So, I would guess that you got lucky and were able to run in single
channel mode at 800FSB/DDR400, but, with two sticks, no go.

Not sure if you are trying to get it to run in dual channel mode, but
perhaps that is the problem--trying two sticks, single channel, at
DDR400 might work...but, as the manual says, no guarantees.

HTH,

BC

> It says that "DDR 400 is not a default configuration".
>
> The FSB for this chipset is listed as 533/400--
>
> ....
>
> So, I would guess that you got lucky and were able to run in single
> channel mode at 800FSB/DDR400, but, with two sticks, no go.

You are right. This board supports a 800 MHz FSB with PC3200 using
overclocking. It works just fine with one stick of PC3200 and should
work with "approved" sets of 2+ sticks... but apparently the couple I
have aren't good enough even though they both run at 400 MHz and are
both CL3. They don't necessarily need to run in dual channel mode but
I sure don't want them defaulting to 266 MHz.

> Not sure if you are trying to get it to run in dual channel mode, but
> perhaps that is the problem--trying two sticks, single channel, at
> DDR400 might work...but, as the manual says, no guarantees.

According to the manual, there are certain slots you should use if you
are trying to run in dual channel mode but no matter what combination
of slots I use, I get 266 MHz. It looks like I'm hosed. I'm just
going to send them back. This computer is not worth the headache.

Brandon wrote:
>> It says that "DDR 400 is not a default configuration".
>>
>> The FSB for this chipset is listed as 533/400--
>>
>> ....
>>
>> So, I would guess that you got lucky and were able to run in single
>> channel mode at 800FSB/DDR400, but, with two sticks, no go.
>
> You are right. This board supports a 800 MHz FSB with PC3200 using
> overclocking. It works just fine with one stick of PC3200 and should
> work with "approved" sets of 2+ sticks... but apparently the couple I
> have aren't good enough even though they both run at 400 MHz and are
> both CL3. They don't necessarily need to run in dual channel mode but
> I sure don't want them defaulting to 266 MHz.
>
>> Not sure if you are trying to get it to run in dual channel mode, but
>> perhaps that is the problem--trying two sticks, single channel, at
>> DDR400 might work...but, as the manual says, no guarantees.
>
> According to the manual, there are certain slots you should use if you
> are trying to run in dual channel mode but no matter what combination
> of slots I use, I get 266 MHz. It looks like I'm hosed. I'm just
> going to send them back. This computer is not worth the headache.
>

Two sticks has twice the memory bandwidth of a single stick.
That leads to a better balance between the needs of the
processor and the output of the memory subsystem.

And the final arbiter, is not all the arithmetic, but how the
system benchmarks. A benchmark takes into account all the
factors, and shows you are result on a stopwatch, or in
framerate in a game. That is the best way to determine
whether your upgrade was worth it or not. So, before
returning the memory, I'd do some runs comparing a single
stick of RAM, versus two sticks.

In terms of upgrades, the processor core clock is the most
important number. Beefing up memory tends to have a
secondary effect. You might see a 10% improvement in
applications, due to modifying the memory situation. But
*your* benchmark results are the only ones that count, not
my guesses.

As an example of the numbers. A processor has a 64 bit interface.
That is 8 bytes. FSB533 * 8 = 4264MB/sec. A single DIMM has
an 8 byte interface. DDR266 * 8 = 2128MB/sec. When two DIMMs
are used, then there is double the bandwidth or 2128 * 2 = 4256MB/sec.
(Really the same number as the above, just some rounding errors.)
In this example, the processor and memory subsystem are
"balanced". If you only had one DIMM, then on a read transfer,
the processor would have to wait a bit.

So there is some benefit from the second stick, but you need
to measure whether the things you do, are speeded up by
your purchase or not. Don't just return the memory, because
you weren't able to "push the memory to the wall". Decide
based on the performance you got for the dollars.

Table 2 in the user manual, shows the ratio of rates supported
by the memory dividers in the Northbridge. The max memory
rate is affected by the choice of FSB. In cases where there
is a choice (like 333/266), you may be able to influence the
choice, by making a manual setting in the BIOS.

AI Overclock Tuner [Manual]
DRAM Frequency [333MHz or 266MHz] refers to DDR rate

HTH,
Paul

I know this is not exactly a timely addition, but I thought you might feel better Knowing you aren't alone.

I too have a C Class p4 on an Asus P4P8X (and the box had a C-Class Compatible sticker on it) and with a single stick of 512 Corsair CL2 XMS it runs. Drop a second in (in D-Channel or other wise) and the system "Recovers from a failed over clocking attempt" I've run it in the 266 compatibility mode, and while Load times are stellar in many games (World of Warcraft, Counter-strike, HL2, Dawn of War, and a bunch of others) The Frame rates are nearly unplayable.

Also I'd like to note that I'm running with paired Model numbers as far as the ram goes, Both sticks are Corsair XMS CMX512--3200C2 (XMS3202V1.2)

[World of Warcraft - Molten core 40 man instance]

• 512mb(1 stick): 55-60 fps (v-Sync'd)
• 1.0Gb(2 sticks): 4-7 fps

[Counter-Strike Source]

• 512mb(1 stick): 45-50 fps
• 1.0Gb(2 sticks): 10-12 fps

Those are all I remember at this point (found this issue back in October of last year) I had a Hardware friend take a look further for me (works in a repair shop versus me being a Software engineer/Hardware hobbyist) and One of the guys he worked with had had a similar experience and was able to "over come it" though juicing up the vCore a tick or two... I've however read a few articles about the P4P8X having issues with vCore adjustments, and have since decided to just hold off and replace the Mobo/Proc/Ram/Video Card with something a little more Current and donate the 1.0 gb to my Wife's Athlon box that actually works at a true 400Mhz...