FSB Memory & Processory - do they need to match?

[DEfusion]

I'm wanting to swap around a couple of my machines and am a bit confused about the FSB.

I have a XP 2000+ which I believe has a FSB of 266, I also have 512Mb of PC 2100, also with a FSB of 266 I think.

However I want to upgrade to a gig of ram and was wondering if I should go for a full gig of PC 3200. But will the FSB of the PC 3200 be compatible with my processor or will my processor drag it down to 266?

My motherboard is a K7S8X ASRock with a maximum FSB of 333 and DDR at 400.

It's been a while since I've been really into building my machines and I feel I've missed out on the explanation of all this.

Any help is greatly appreciated.

-D

[tbl_001]

Scroll down to a guy called raddish - he seems to have it sussed:

http://www.slickdeals.net/forums/showthread.php?t=24045

Basically though, yes for AMD, no for intel chips.

[Jarhed7276]

If you put PC3200 in with PC2100 both memory sticks will operate at the speed of the slowest stick without any problems regardless of the make of the CPU.

[John Prophet]

if you mix pc3200 with pc2700 the 3200 will just run at the speed of the 2700....or if u mix one of those with pc2100 it will run at 2100

as far as the fsb of the cpu and the speed of the ram..that is a little harder to say because a lot of it depends on the motherboard...in other words the options in the bios....in some bioses the ram speed is locked to the fsb of the cpu...but in some bioses you can run the ram and cpu fsb "asynchronously" or "at different speeds"

for instance I have one comp with an old slot A athlon.....it runs at a 200fsb (or 100X2)...and I have PC133 ram.....so if the ram and cpu were locked together it would mean the ram ran at pc100.....but luckily there is a setting for the memory in bios where you can set the ram speed to "cpu+33mhz"....so I run it there and my ram runs at PC133 speeds.

So that part of it depends on the options in the bios

[tbl_001]

DeFusion - John is referring to overclocking which opens up a whole array of possibilities.

From what I have found is that without overclocking, CPU FSB for AMD chips need to be synchronised, whereas Intel chips take any old combination - as John states - asynchronously. Probably why they cost so much!

I suppose it depends wether you feel comfortable overclocking or not, some don't.

400DDR Ram on a new Main board with an AMD 333 FSB would underclock the memory to 333hz. So technically they don't need to be the same as the board synchs them automatically to be the same.

[John Prophet]

hmmm, I am not sure about AMD chips needing to have the same fsb and ram speed....I am pretty sure that lots of the boards allow you to run an athlon at 333 and the ram at 400....and that isnt really overclocking if the ram is DDR400

[tbl_001]

Yep, as I said they do not need to be the same because the board will set the memory speed automatically - else it would run slower. This is only AMD chips.

You can put 400DDR with a 333 FSB AMD chip but it runs the DDR @333. This isn't overclocking but underclocking - and it's all done by the board not the user.

When I refer to overclocking in my message I am on about "cpu+33mhz" - that is overclocking.

Check out the link I put in at the top. This is in many groups.

[beppodmime]

John, alot of current Socket A chipsets do allow you to run both the memory and CPU clocks out of sync, but with chipsets such as nVidia's nForce2, running the memory clock faster than the CPU clock actually DEGRADES performance. Whether this applies to other chipsets for Socket A CPU's or not, I'm not sure. Only way to tell would be to run benchmarks.

But as far as the CPU needing to operate at the same FSB and RAM speeds, no it's not a necessity. Modern chipsets manage both the memory and CPU host clock independently of one another, so running the CPU at a FSB of 266DDR and the memory at 400DDR is possible, depending on the motherboard.

Looking at the specs for the board here:

http://www.asrock.com/product/product_k7s8x.htm

EDIT: according to the manual, you can only have ONE stick of PC3200 memory installed in order to get PC3200 speeds out of this board. If you want 1GB, make SURE you get ONE 1GB stick of PC3200 if you really want to run at that speed, otherwise the board will operate the memory at PC2700 for two sticks, or PC2100 for 3, regardless of how fast the memory is rated. With a max of 1GB per stick per bank, that means you can run 1GB of PC3200, 2GB of PC2700 or 3GB of PC1600/PC2100

[DEfusion]

Originally Posted by beppodmime

according to the manual, you can only have ONE stick of PC3200 memory installed in order to get PC3200 speeds out of this board. If you want 1GB, make SURE you get ONE 1GB stick of PC3200 if you really want to run at that speed, otherwise the board will operate the memory at PC2700 for two sticks, or PC2100 for 3, regardless of how fast the memory is rated. With a max of 1GB per stick per bank, that means you can run 1GB of PC3200, 2GB of PC2700 or 3GB of PC1600/PC2100

Thankyou all for your help.

So will I be best opting for another PC2100 512 stick for now? Or will the future-proofing of 2 sticks of PC2700 mean if I choose to upgrade the processor then the FSB of the memory & CPU will raise to the 333 level of PC2700?

Thanks again,

-D

[sweeper2]

i would go with (2) sticks of pc2700, so you can upgrade your cpu later to a 333 FSB and it will match your PC2700 ram.


i run an Athlon xp2500 at FSB of 333 with PC3200 running at DDR400 speeds, havn't noticed any problems with decreased performance...?

my MB allows me to run my mem and cpu at different bus speeds...