Old memory to New system?

[dodger]

About to bump the old system from 256 to 512DDR as a last step before major upgrade, when another question reared its ugly head. Present memory is PC2100. I have an FSB of 266 mhz. I will upgrade to an FSB of 400 mhz and an Athlon XP 2500 or better with an appropriate motherboard. Here's the question(s) will my old PC2100 memory stick still be useable on a faster system? Should I add a PC2100 or a faster stick now? If so, how will a faster stick behave on my present system? Thanks to all of you for a great forum!!

[Delta_]

It will but i would not recommend it, with a 2500+ which uses a 333fsb you need to use PC2700, for anything with 400fsb use PC3200.  The reason is because you will bottleneck the system and it will not run very fast at all.  A 1:1 ratio is best.  

[congo]

Forget about PC2100 RAM, don't ever buy it again, you can't use it on a faster FSB.

PC2100 is designed for 266mhz FSB.

PC2700 is designed for 333mhz FSB.

PC3200 is designed for 400mhz FSB.

The current "value" upgrade would be an nForce2 chipset mainboard with a CPU of 333mhz FSB speed.

If you get a more expensive 400mhz FSB CPU, the nForce2 chipset will take that as well.

If PC3200 is about the same price as the PC2700 ram, get it, because you can use it when you upgrade to a 400mhz FSB CPU, or in a P4 machine if you ever went that route.

AMD rigs run better by far, if the RAM, CPU and FSB are all in sync as far as the speed (FSB mhz) is concerned.

Thus, if you buy a CPU with a 333mhz FSB speed, and you buy PC3200 (400mhz ram), run the RAM degraded to 333mhz. It will actually make the PC faster.

There is another advantage to running PC3200 at 333mhz in that situation. The RAM timings can be set to "turbo". ie. 6-2-2-2 or CAS2.0 latency (with a good budget brand of RAM, such as Kingston Value Ram) and the FSB can be overclocked slightly with little risk to system stability.

Hope that helps.

[dodger]

  Many thanks folks, that clarifies the whole picture. Congo, I had already decided to go with the N-force 2 chipset and I will almost certainly go with 400 mhz. So I could swap in  a 512 MB of PC3200 now for some memory increase even though the speed would be degraded?

[congo]

You should be able to, but first, a warning.........

You should buy two IDENTICAL ram sticks for the dual channel mode on the nForce chipset.

I try to achieve this by buying two sticks at the same time from the same supplier, from the same batch.

If you buy one now and one later, you might find the sticks less than compatible for dual channel memory mode.

[dodger]

         Thanks, congo. I'll do just that. Cheers