John said:
First off I would like to thank everyone that replied to my posting, all
replies have been copied and saved.
Since I first posted my problem with memory on my friends computer I've
spent sometime reading up on memory problems (most of which went over my
head)but there are a few points that seemed interesting;
* With Asus motherboards you need to disable legacy usb in the bios for
Memtest86+ to work correctly - has anyone heard about this and if so, is it
correct?
It was true at one time. That may not have been an issue with all motherboards,
but a select few. Both the motherboards, and memtest, have changed since
then.
Memtest, relies on a certain standard, for reserved memory areas.
Memtest won't test the very lowest memory, because the BIOS may still be
using it. Memtest relies on the information the BIOS gives it, to not
cause a conflict.
* Reduce memory bus speed. How would I do this?
1) Download the user manual (PDF format) from support.asus.com
2) Change "Ai Tuning" to [Manual]. That should expose more settings for
manual adjustment. I usually spend 30 minutes going through a BIOS,
setting things to manual, and seeing what extra settings get added
to the list.
3) See "FSB and Mem Config" in the manual, to adjust the memory clock.
"Linked" mode, implies standard ratios between FSB and memory clock.
"FSB - Memory Ratio" applies a particular divider.
For an example, say you're using a FSB1066 processor at stock.
The FSB is a QDR interface or quad data rate.
Divide by 4 to get the actual CPU input clock.
1066/4 = 266MHz CPU input clock. Now, use a memory divider of 3:2.
That gives 266*3/2=400. Multiply that memory clock by 2 (double data
rate memory type) to get a DDR memory rate of DDR2-800 (PC2-6400).
If you went from 3:2 down to 5:4, the math gives DDR2-667 (~ PC2-5300).
4) If you use that control, you can leave the timings at Auto.
If you crank the CPU clock manually, that throws off the BIOS
calculation of timing values, and you should do the math yourself
and scale them, according to the final memory clock you've set up
for yourself. If the clock is at stock (like 266Mhz for FSB1066),
then the BIOS should be able to interpolate the correct values, out
of the values listed in the memory DIMM SPD EEPROM chip.
5) There is also a Command Rate setting. 2N is more relaxed than 1N,
and limits address transmission to every second cycle. On
older systems, it was only needed for four DIMMs. On modern systems
now, with sky-high memory clocks, 2N is needed even with one DIMM
per channel.
In the manual, look for "Command Per Clock" and test with [2 Clock]
and see if stability improves.
6) In terms of timing adjustments, if the CAS was 5, that is five
clock ticks. Each clock tick on the memory, has a period in nanoseconds.
So when you talk of 5 ticks, you could be speaking of 12.5 ns worth
of time. When the memory input clock is changed, the 12.5ns parameter
you're trying to meet, doesn't change. You still want to request
data to arrive 12.5ns later. Say the new clock period was 2 nanoseconds
(i.e. higher clock). 12.5/2 = 6 plus a little bit, which you round
up to 7. So you'd go into the BIOS, and change CAS from 5 to 7, if you'd
raised the clock. You can dispense with a traceable calculation, and
just scale the numbers by the ratio of the clocks (if you can figure
that out). For example, say by playing with just the CPU input clock
(i.e. overclocking the CPU), I'd actually forced the memory from
DDR2-667 to DDR2-800 and CAS was 5 at 667 (said so on the packaging
the memory came in). I could guess at the new CAS value as 5*800/667
or 6 exactly (since there is no fractional part, there is no need to
round up).
But in your case, you're not changing the CPU input clock from the
stock value. And if you do that, the BIOS should calculate the timing
properly on its own. You can use CPUZ while in Windows, to verify the
effects.
I should note, that this isn't always true. The BIOS being good at it
The computer I'm typing this on, doesn't know how to scale properly,
and ran my RAM with a CAS which was too tight. And the RAM still
passed
But when I checked CPUZ, that really pissed me off, because
I prefer to be in control. I don't want my hardware trashed, because
some BIOS designer couldn't do their job. At the time, I wasn't trying
to overclock, but discovered soon after that the BIOS had cranked stuff
on me, and not corrected the CAS. According to the specs, the computer
should have crashed immediately.
*With memory timings is it just a simple task of changing the bios as this
setting shown here? CAS-tRCD-tRP-tRAS 2-2-2-5 - i.e. CAS 2 tRCD 2 tRP 2
tRAS 5?
The DDR2 memory, will be using higher values than that. I've got DDR2
in this machine, and I own a pair of CAS4 and a pair of CAS5 memories.
Like perhaps 5-5-5-18. So expect to see higher than 2-2-2-5, which is
an older, enthusiast DDR400 spec. (On some of the DDR3 stuff, with
sky high clocks, they're up around CAS 9.)
It will be a few days before I have access to the computer so the more
information I get now the better
Thanks.
Plenty of "fun" ahead.
Paul
