okenido wrote:

Hello

I have the choice between using PC133 or PC100 sticks for my build. They are both CAS3, and no matter which one I choose, they'll run @100mhz FSB.

I was wondering if choosing the PC133 is better. Will PC133 CL3 sticks act like PC100 CL2 when forced to run at 100mhz ? I can't check since it's an Intel SE440BX-2 motherboard, there are no options to tweak RAM timings.

Diagnostic programs like Astra (DOS) or CPU-Z (Windows) can read the module's SPD. It may contain a 100/cl2 profile and in that case the motherboard (BIOS) probably uses it to set up its memory controller.

My bet is that the PC133 CL3 will run fine at PC100 CL2.

Probably even run at PC133 CL2 unless it is super cheap stuff.

Don't forget about tweaking the other timings as well.

I have not had any issues running PC133 sticks at CL2 @ 100MHz in any of my machines.

all the cl3 pc133 that I ever tried to run at 100 cl2 worked fine at that;

If you look at the datasheets or specs of PC133 RAM you will often see it's both been rated for PC133 @CL3 and PC100 @CL2.

I believe the OP is more interested in whether his board will actually use CL2 as it has no manual timing settings.

This is simple to answer if you look at the actual requirements in terms of chip cycle time.

PC100 CL2 = 8ns
PC133 CL3 = 7.5ns

So 7.5ns SDRAM is more than capable of supporting 100MHz at CL2.

As for what an SE440BX with limited settings would do in this case - no idea, test and see...

Thanx 😀
I downloaded CPUZ version 1.78 which supports Windows 9x, and managed to find a PC133 stick that has a SPD profile for 100mhz @CL2. The board will run it at CL2 only if it has the profile for the required frequency. Some of my 133mhz sticks doesn't have the SPD profile for 100mhz, so it seems (relatively) important for people with Intel or OEM boards that doesn't allow to mess with this in the BIOS

dionb wrote:

This is simple to answer if you look at the actual requirements in terms of chip cycle time. […]
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This is simple to answer if you look at the actual requirements in terms of chip cycle time.

PC100 CL2 = 8ns
PC133 CL3 = 7.5ns

So 7.5ns SDRAM is more than capable of supporting 100MHz at CL2.

Yes, for clarity, the CL2/CL3 rating means 2 or 3 clock cycles respectively.
The higher the clock frequency, the shorter the absolute time. So CL3 at 133 MHz is faster than CL3 at 100 MHz. And as the calculations show, CL3 at 133 MHz is even faster than CL2 at 100 MHz.

I'm not sure if this will apply to you, but I had a heck of a time getting my Dell Precision Workstation 410 (440BX) working with 1 GB RAM at CL2 PC100. I don't remember if it was a particular density issue, or if it was that some PC133 sticks I had were missing PC100 information on them, but if you run into trouble, I can look up the specs of the actual 256 MB ECC/REG modules that worked in this board. It could also be that when I was looking, there just wasn't much supply for what I wanted.

I read somewhere that it could only handle three sticks of double sided RAMs at low latency, then adding a fourth would force it into a slower mode (?). I don't remember where I read this unfortunately, i'm not even sure it was for the 440BX or the Via Apollo Pro 133A.
At the end, did you managed to run the whole system @CL2 ?
I won't have this problem since I only have 384 MB. It's a Pentium II machine 😀

Yes, I was able to run the whole system at CL2. I think I specifically used PC100 CL2 sticks rather than PC133 modules.