A7N8X Deluxe - more memory = slower? or Corsair XMS = slower?

  • Thread starter Thread starter Erik Harris
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Erik Harris

I've got a system based on an A7N8X-Deluxe (1.04, latest BIOS) board and an
Athlon XP 2400+ CPU running at 166x12.5 (recognized as a 2600+ upon boot).
Until a few minutes ago, I had a single stick of OCZ PC3500EL memory in my
machine. Good stuff, very highly rated (unlike many of OCZ's other products,
including their other memory products). When I decided to upgrade my system,
upon seeing that I can't find this particular memory anywhere, I figured that
I might as well just put it in Cheryl's new machine and get a matched pair of
sticks for myself, to run in dual pipeline mode (which I understand yields a
very small 1-3% boost on nForce2 motherboards, but if I'm doubling my memory,
I might as well do it). I picked up a pair of the highly-rated Corsair XMS
PC4000 sticks. Their memory timings are rated slower than those of the OCZ,
but as I understand it, running memory at speeds lower than its rating let
you speed up the timings. Is this true? Since I'm only running a 166MHz bus
(PC2700), my reasoning was that both the PC3500 and PC4000 should allow me
scads of headroom, and would both continue to give me headroom once I install
my 3200+ CPU, even if I overclock it a bit from its default 200MHz bus speed
(the new CPU is sitting here, but the new heatsink/fan isn't scheduled to
arrive until Monday).

I had the OCZ stick running at 6-2-2-2 (I don't recall its rated timings; I
think they might have been a little bit higher). When I dropped the two
supposedly-faster Corsair chips in and booted my system, I had to reboot five
times before it would detect my keyboard (USB, dunno if it would've detected
a PS/2 keyboard more easily), and when it did boot, it dropped my bus speed
to 100MHz and recognized my CPU as an Athlon 1800. Ditto for a second try,
after checking the BIOS to make sure it registered all of my memory. As soon
as I put the memory settings at their default setting (7-3-3-3), it booted up
just fine. I'm sure I can lower them again, but obviously not back to where
they were with the old RAM.

I seem to come up with two possible conclusions (and a third that's almost
the same as the second):

1 - Two years ago, OCZ was making slower-rated memory that's faster than
Corsair's current top of the line memory (second only to their PC4400 RAM in
the same product line)

2 - Having multiple memory chips taxes the A7N8X-Deluxe enough that it can't
use memory timings that are as aggressive

2a - Dual pipeline mode taxes the A7N8X-Deluxe enough that it can't use
memory timings that are as aggressive

Anyone happen to know which is the case?

--
Erik Harris n$wsr$ader@$harrishom$.com
AIM: KngFuJoe http://www.eharrishome.com
Chinese-Indonesian MA Club http://cimac.eharrishome.com

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Replace each dollar sign with an "e" for the correct address.
 
I seem to come up with two possible conclusions (and a third that's almost
the same as the second):

1 - Two years ago, OCZ was making slower-rated memory that's faster than
Corsair's current top of the line memory (second only to their PC4400 RAM in
the same product line)

2 - Having multiple memory chips taxes the A7N8X-Deluxe enough that it can't
use memory timings that are as aggressive

2a - Dual pipeline mode taxes the A7N8X-Deluxe enough that it can't use
memory timings that are as aggressive

Anyone happen to know which is the case?
Click to expand...

With two sticks your motherboard should now be using interleaved memory
assess. That usually isn't done with one stick. Possibly timeings are more
critical when running in interleaved mode. You should run some benchmarks to
see just how good you old & new system performs. AIDA32 has a memory
read/write benchmark program.

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Erik Harris said:
I've got a system based on an A7N8X-Deluxe (1.04, latest BIOS) board and an
Athlon XP 2400+ CPU running at 166x12.5 (recognized as a 2600+ upon boot).
Until a few minutes ago, I had a single stick of OCZ PC3500EL memory in my
machine. Good stuff, very highly rated (unlike many of OCZ's other products,
including their other memory products). When I decided to upgrade my system,
upon seeing that I can't find this particular memory anywhere, I figured that
I might as well just put it in Cheryl's new machine and get a matched pair of
sticks for myself, to run in dual pipeline mode (which I understand yields a
very small 1-3% boost on nForce2 motherboards, but if I'm doubling my memory,
I might as well do it). I picked up a pair of the highly-rated Corsair XMS
PC4000 sticks. Their memory timings are rated slower than those of the OCZ,
but as I understand it, running memory at speeds lower than its rating let
you speed up the timings. Is this true? Since I'm only running a 166MHz bus
(PC2700), my reasoning was that both the PC3500 and PC4000 should allow me
scads of headroom, and would both continue to give me headroom once I install
my 3200+ CPU, even if I overclock it a bit from its default 200MHz bus speed
(the new CPU is sitting here, but the new heatsink/fan isn't scheduled to
arrive until Monday).

I had the OCZ stick running at 6-2-2-2 (I don't recall its rated timings; I
think they might have been a little bit higher). When I dropped the two
supposedly-faster Corsair chips in and booted my system, I had to reboot five
times before it would detect my keyboard (USB, dunno if it would've detected
a PS/2 keyboard more easily), and when it did boot, it dropped my bus speed
to 100MHz and recognized my CPU as an Athlon 1800. Ditto for a second try,
after checking the BIOS to make sure it registered all of my memory. As soon
as I put the memory settings at their default setting (7-3-3-3), it booted up
just fine. I'm sure I can lower them again, but obviously not back to where
they were with the old RAM.

I seem to come up with two possible conclusions (and a third that's almost
the same as the second):

1 - Two years ago, OCZ was making slower-rated memory that's faster than
Corsair's current top of the line memory (second only to their PC4400 RAM in
the same product line)

2 - Having multiple memory chips taxes the A7N8X-Deluxe enough that it can't
use memory timings that are as aggressive

2a - Dual pipeline mode taxes the A7N8X-Deluxe enough that it can't use
memory timings that are as aggressive

Anyone happen to know which is the case?
Click to expand...

Apparently, you cannot tighten the timing on the high clock memory,
as much as the math of the matter would suggest. I don't have a
good explanation for it. At PC4000 and CAS3, that is DDR500, a 250MHz
clock with a 4ns period. 3 cycles * 4ns = 12ns for CAS. With a clock
of 166MHz, the period becomes 6ns. 12ns for CAS divided by 6ns period
equals CAS2. So, by that simple minded arithmetic, CAS2 should have
worked. I don't know why it won't run CAS2, as I don't know enough
about the way CAS timing works inside the memory chip.

The OCZ probably used Winbond BH-5, which is a memory that supports
low latency, and is no longer made by Winbond. BH-5 runs CAS2 at
DDR400 and will do a little bit more in terms of overclock (that is
perhaps how it got its PC3500 rating). Now, many performance memories
have a heat spreader on them, to cover up the names, and I don't
recommend tearing it off to find out. Usually, the manufacturer
will claim the warranty is void if you remove it.

One review site article I read, suggested that a tight CAS isn't as
important at DDR400 or above, as some of the delays are pipeline,
and the memory is busy all the time anyway. I wouldn't lose too much
sleep over having to run at CAS3.

The original reviews of the Nforce2 boards found you could run three
sticks at CAS2 at DDR400. Now, while chips sometimes get modified
during production, I'm guessing it isn't the chipset that is
responsible. It could be the BIOS, and there is at least one poster
here who had one memory channel dead, until he used the latest BIOS.
So, depending on what Asus has been playing with in the setup of
the chipset, anything is possible.

If you can boot into windows, use a utility to check the ram timings,
to make sure what you see in the BIOS setup screens, is actually
what the memory is set to.

Some of the datasheets actually say that low latency settings are
not recommended. For example, this 3-4-4-8 memory says:

http://corsairmicro.com/corsair/products/specs/twinx-3700.pdf

"Operation not recommended at low latency values"

In that datasheet, you will also notice, that even though their
example DDR467 runs at CAS3, it offers a higher bench than the
DDR434 CAS2 they are comparing it too. The purpose of 3-4-4-8
memory, is to allow as high a memory clock as possible, to give
better memory bandwidth.

HTH,
Paul
 
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