Re: can I use cl3 memory instead of 2.5 ?



Tom wrote:
Thanks Paul for the very detailed info. I did give the new memory (ie.
512mb 400 ddr cl3) a try but the XP conked out halfway through loading
and re-booted... every time I tried it. I don't know if the memory is
duff. I did try this using the new module without the original memory
installed. With both new and old modules in the MB it refused to boot.

Then I saw a bios upgrade for my MB the MSI KM400 (KM4M-L) (on MSI's
site) that supposedly made 400mhz memory run ok at 333mhz (there must
have been an issue with this faster memory at some point ?) - but I'm
not sure yet I dare flash the bios....

Thanks again for your help.

I wouldn't flash the BIOS quite yet.

First of all, does the BIOS feature set, match the manual here ?

http://download2.msi.com/files/downloads/mnu_exe/E6734v1.5.zip

(Motherboard picture here as well.)

http://www.msicomputer.com/product/detail_spec/product_detail.asp?model=km4m-l

The steps I'd try

1) Don't boot into Windows, after changing the memory subsystem. Your
first boot environment, should be a memtest86+ floppy or CDROM version.
( memtest.org ). The idea is, you test the memory first, with memtest,
and only boot into Windows when the memory is completely error free.
If you don't do this first, it is possible to corrupt your Windows
install. So even if you tune the memory correctly now, there is a small chance
that Windows still won't boot.

2) I looked for evidence of chipset problems. I looked at the vip.asus.com
forums, for A7V8X-MX, which is a KM400 board as well. There seem to be
a few problems, but nobody really ironed out the details (like a suggested
recipe).

Your BIOS has manual tuning features.

The user manual says the chipset supports async relationships between the
memory and FSB. So your processor could be run at FSB333, and the
memory could run at DDR333 (sync) or DDR266 (async) and both should
work. There were some other VIA chipsets, where the FSB choice affected
the DRAM clock choice, making tuning more destructive to overall performance.
You don't have a limitation there, according to the manual.

If DDR333 won't work for the memory, switch to DDR266 with the two
sticks of RAM.

In "DRAM Clock/Drive Control"

DRAM Clock [133MHz] # That sets memory to DDR266
DRAM Timing [By SPD] # I'm being a chicken here. Most BIOS
offer Auto for all settings in the Detailed
section, but this BIOS doesn't seem to. I
was hoping to just dial in 3-3-3-8 timing,
but I don't know how some of the settings
should be adjusted.
DRAM Voltage [2.6V or 2.7V] # Probably won't make a big different, unless
the normal value was too low by accident.

The memory settings I was interested in, are the following. When a person says
they bought 3-3-3-8 memory, the settings correspond to

DRAM Cas latency Tcas Column Address Strobe (Read) to data
DRAM Ras precharge Trp Precharge command period
DRAM Ras to Cas delay Trcd Active to Read or Write
DRAM Precharge delay Tras Active to Precharge delay

The BIOS screens don't list them in the proper order, so you have to be
careful when adjusting them. CAS is in 0.5 steps. The others are in steps of 1.
I was hoping to make the timing more slack, as in the 3-3-3-8 numbers.

Another one of interest, is the "command rate" setting. When this is
offered, it increases the time an address/command is placed on the bus.
Two cycles helps when the bus is heavily loaded. The one cycle setting
means you can stuff more commands on the bus in a given time interval,
meaning more performance. But if a RAM is not stable, command rate 2T
can help.

DRAM Command Rate [2T]

The bank interleave referred to in your BIOS, is banks inside
the DRAM chips themselves. I would expect 4 bank is supported, but
I'd have to download a memory datasheet again, to refresh my memory
on the bank structure. It is possible the 2 bank variety only existed
early in the life of DDR memory. Setting this is more of a nuisance
than anything, and this is an example of something I'd prefer to just
leave at "Auto".

The "Trans Non-DDR400/DDR400" listed in the manual, could actually be
a reference to Tras, which is the larger number in the list of four timing
settings. The second number could be Trc. (Tras + Trp = Trc ???)
When five timing numbers are given, the last one could be Trc. I'm
not sure why they're offering options that way.

If you have insomnia, this is the memory chip datasheet I looked at,
to try to figure out whether the second number might be Trc.

http://download.micron.com/pdf/datasheets/dram/ddr/512MBDDRx4x8x16.pdf

Anyway, starting with [By SPD], allows the BIOS to work its normal
automatic magic. For your first experiment, you can just drop the
DRAM clock, run memtest86+ for a couple passes, and post back as
to how much of a difference that made.

If you do decide to flash the BIOS, at some future date, make
sure you have a stable memory configuration before doing it.

In your user manual, I notice the BIOS chip is soldered to the
motherboard. If the BIOS flash goes bad, you're not going
to be able to replace that chip (easily). A good motherboard
provides a socket for that chip, so it can be pulled and replaced.
Working on these motherboards isn't easy, because the copper foil
used is so flimsy. To replace your BIOS chip, I'd use my $100.00
pair of miniature diagonal cutters, and cut the legs off. Then
unsolder and clean the pads underneath. There is also a desoldering
aid called ChipQuik (low temperature alloy you add to the solder), which
is another way to ease the desoldering process. i don't own any of
that, but one poster uses it a lot, to help remove pesky ICs.
You don't even want to go there... Trust me.

Paul
.