PC3200 I think. Its the fastest. Bigger number is best.
Dan

Gixer:

Spec on my memory modules read as follows:
PC400512MB DDR . I have two installed.

My CPU:  AMD Athlon XP 2600+
400*/333 MHz FSB Support (*PCB 2.0 or later version)

I believe I have the PCB 2.0. My Bios frequency setting is at 133MHz, Multiplier in Auto. Do I have the correct type DIMM modules? From what you said, I should be using a PC2700DDR. Would it make any significant improvement to change from the PC400DDR to the PC2700DDR?

ANY DIMM stick will switch down to the maximum speed the MOBO can handle or the max speed of the slowest installed DIMM
This has certain limits, as they usually take the closest pair: 400/333, 333/233, 133/100.

Doesn't really matter if you put faster DIMM in a slow MOBO, just check if the MOBO speed is supported

is the same... bus speed is 400MHz

Should be written as PC3200 DDR400 though

Here is the funny thing though Bubblehead..........

It will actually run faster if you slow the RAM down.

Your CPU and front side bus run at 333mhz.

In most AMD rigs, the RAM run at the same speed as CPU and FSB produces a "syncronised" system and it will outpace any other configuration on the PC.

The reason is that the faster ram data has to be re-calculated at the lesser bus speed and this slows performance.

The PC3200 400mhz DDR RAM modules you have are over-rated for your PC........... but...........

If you learn about the RAM timings as Gixer suggested earlier, you'll find you can get some  of that locked in performance  back out of it.

You need to set the RAM (memory speed) to 333mhz in your bios manually to obtain the highest performance as it will almost surely be set now to configure automatically to 400mhz via the RAM chips SPD module.

Sure Gixer, lots, and I thought most modern boards will run the ram faster than the CPU. Check it out.

What I was reffering to was the RAM, if configured by
SPD, will run at it's default or "safe" timings.

Those timings can be over-ridden by setting them manually. So, if you have PC3200 running at a lower speed,
then the timings would be able to be tightened up without problems.

I've been absorbed in the inner workings of IL2-FB, and I also
have been experimenting with WinXP (well, butchering XP  ) . So I think I have WinXP finally under some sort of control now, maybe the formatting is over for a while, touch wood!

Gixer,

That's because your mainboard supports UP TO PC3200 at standard clock speeds, and because it's 64bit, that may be all it supports, not sure about your particular board.

Take the nVidia nForce2 Ultra 400 chipset as an example, as it is a common and typical chipset.............

It supports 200/266/333/400 mhz FSB speeds and RAM speeds up to 400mhz (PC3200).

Say I drop in an XP2600+ CPU......  and then add PC3200 RAM.......  it will happily run the CPU and FSB at 333mhz while the RAM itself is clocked at 400mhz.

VIA, SIS and many others will do this and have been doing it for a few years.

Another example is the P4 Northwood CPU based chipsets which ran on a 533mhz FSB while the RAM was typically running at 266mhz (PC2100), but then they would also run the faster, newer RAM modules as they became available or affordable.

Take a 800mhz P4 based rig, which is meant to run PC3200 ideally, yet it will happily run with PC2700 installed (though performance will be compromised), as will a 400mhz FSB AMD CPU based rig.

As for the SPD module, (a tiny black chip on each ram stick), it simply supplies information to the mainboard so that (when SPD is enabled in BIOS settings) the mainboard can resolve the best safe speeds to run the ram at.

If the hardware configuration is non-standard, or non-ideal, the SPD should be switched off and the RAM timings should be done manually if possible. Some amount of experimenting here is usually done to obtain the fastest timings possible which do not produce errors. Benchmarking tools are required to get evidence of performance differences at different timings.

The non-standard (well, sort of) hardware environment of a 333mhz AMD CPU running PC3200 (400mhz) RAM is what I was refering to in this post, and theoretically at least, the PC in question should run better with the RAM running at 333mhz, (in Syncronisation with the CPU and FSB speeds) and the latency timings set manually and overclocked.

The RAM in question may very well handle the overclocked latencies without error, simply because the RAM is now running under it's rated maximum speed.
(now at 333mhz instead of 400mhz).

Clear as mud?

You might remember a while back when VIA brought out an AMD based chipset (KT400*?) which ASUS promptly made a high spec board with. There was considerable debate on the very marginal increase in performance obtained when PC3200 was installed on the system, which did not support 400mhz CPU's (they hadn't yet been released) and the system's were really a 333mhz machine. Other and later chipsets produced better performace with the Speeds all set in sync as far as I'm aware.