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I got (2) 512MG PC400 DDR installed in my AsusA7N8X Deluxe mobo. Manual states it also supports PC3200/2700/2100 DDR RAM memory. Question: Is one type significantly better over the others?  

Bubblehead

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

I take it you mean you have PC4000ddr in there? or do you mean ram running with an FSB of 400?

Basically you want ram that matches the FSB of your CPU.  i.e. if your cpu is has a 400MHz FSB you want PC3200 which is also 400MHz.  If you put slower ram i.e. PC2700 333MHz FSB your system will not be in synch and will not run as well.

It goes the other way too, if your CPU is 400MHz then there is no point putting in ram that is over 400MHz FSB i.e. PC4000 which is capable of 500MHz FSB.  Your PC will actually slow the speed of the ram to match the CPU, so you have wasted your money!

The only time you should get ram with a higher FSB than your CPU is if your planning to overclock your system.  You usually bump up the FSB when overclocking so you require ram that is capable of higher speeds.  Also somtimes you can buy higher speed ram and though it clocks the FSB slower you should be able to tighten the timings a lot to give better performance and the ram still run stable.

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?

Ok I have never heard of PC400 so I take it the ram is probably capable of 400FSB speeds (PC3200)

This shouldnt cause you a problem as your CPU is only 333FSB so it will just down clock its FSB to match it.

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

Gixer:

Something seemed screwy here.  The packge label for the subject memory module listed it as:  512MB/PC3200 DDR while the label right on the module itself liste it as:
PC400 512MB DDR. Are these the same and one?

Bubblehead

is the same... bus speed is 400MHz

Should be written as PC3200 DDR400 though

Yup as Ivan said it is PC3200 stuff which has an FSB of 400.  They just written it weird on the ram.  Looks like the ram is slightly wasted as your CPU is only 333MHz FSB but dont worry about it as it will all run fine the way it is!

Its only if your ram is slower than the CPU you got problems.

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.

Congo if its set to SPD it will clock the ram to the same speed as the CPU

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  ;D ) . So I think I have WinXP finally under some sort of control now, maybe the formatting is over for a while, touch wood!

I cant get the FSB of my ram running faster than my CPU and I got a pretty up to date mobo. Saying that mine is AMD64.  Maybe the Pentiums can, and I dont know enough about the Pentium setup to comment, though I have heard that the CPU and ram can run outta sync ok on Pentiums.

Yeah you can only format so many times before it gets boring.  I went through a phase of doing it when I had 98se trying to only get what stuff I wanted on my system.  Now I try to format at most once a year!  Its getting hard work re-installing all my FS2004 stuff each time.

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......

I see what your saying there  ;D  I just thought that mobos wouldn't let the ram run at a higher speed than the CPU.