Puzzled about memory speed and FSB

  Totally-braindead 11:07 17 Feb 06
Locked

I've been involved in a thread for the past day or so and got a bit side tracked into a discussion an memory speeds.
Now not wishing to hijack the persons thread or confuse him more, as his particular problem isn't the memory, I've decided to open my own thread on the subject to get some clarification on the subject.

Now I've built perhaps 20 - 30 PCs over the years and never had any real problems with setting memory speeds but my query is this.
I always believed rightly or wrongly that the speed of memory that the system could use was tied to the FSB of the processor. So in the case of a Athlon XP 2000+ for example click here the FSB is 133 x 2 which gives you a FSB of 266mhz which means it will need PC2100 memory which runs at 266mhz.
Now the query I have is this specifically, you can use PC2700 memory which runs at 333mhz but I believed that the processor would drop the speed that the memory runs at to 266mhz as that was the fastest the processor could access the memory.
It has been said that I am incorrect on this and that the memory is capable of running at the faster speed providing its set up to do so in the BIOS. Now I'm perfectly willing to be educated here if I'm wrong, as I have been in the past, but supposing you did set the memory to run faster than the processor and I'm also supposing that won't cause any problems, I would like someone to explain to me how this can work. Surely the processor would bottleneck the speed the memory could go at and if that was the case then how could it actually be any faster? Surely the processor would,because it was slower not be able to address the memory any quicker. What am I missing here?
Please educate me because I must be living up to my username.

  Mark5001 12:59 17 Feb 06

I use an Athlon 3000+ coupled with 2GB of 400mhz DDR ram. Aida reports a 166 X 2 = 333mhz FSB so my ram is faster than the processor ( I think )This gives me a bandwidth of 2666 Mb/s.No bottlenecks or problems of any kind in the 9 months i have been running this setup.

  lionheart777 14:57 17 Feb 06

This may help :

click here

  Jimmyh 17:38 17 Feb 06

Yeh stop hi-jacking my thread :p

After reading that i'd happily keep my PC2100 memory with my AMD Athlon 2000+XP.

But i have also read that amd have seperate buses for the memory and the cpu, not sure if this is true or not, but still i guess that one would still have to wait for the other.

  ed-0 18:29 17 Feb 06

^^^ Bump ^^^

  Totally-braindead 18:34 17 Feb 06

I see you're keeping an eye on this thread as well ed-0.

  ade.h 18:56 17 Feb 06

Me too, TB.

I always thought along the same lines as yourself, as I have read many times in specialist publications and websites that the slowest part of the chain is the controlling influence.

I have always assumed that - although the speed of the DiMMs will not actually drop - the data throughput will be limited to the CPU bus speed.

  ade.h 18:57 17 Feb 06

I say "assumed". Wrong word, really. "Interpreted the available information" is more accurate.

  ed-0 19:10 17 Feb 06

Take the ASrock K7VT4A PRO. Fsb 333Mhz, supports Supports DDR400* high performance memory. click here

The Asus A7V8X-X. Supports 333Mhz cpu click here but can run a 200Mhz and 266Mhz cpu with 400Mhz ram click here.

The duron ( 100Mhz )posted yesterday running pc2100 ( 266Mhz )ram. click here.

  Jimmyh 19:30 17 Feb 06

I'd agree that u can run faster memory on slow cpu's...im using pc2700 with my 133/266 cpu at the moment....but some where along the road the memory will have to wait for the cpu to send information...the memory will be processing it faster than the cpu can send it.

  Totally-braindead 19:58 17 Feb 06

Yes ed-0 I've no problem with that, what I have a problem with is saying the memory will run faster, that is what I want someone to explain. I know you can run faster memory what I cannot understand is the comment that you can run the memory at the faster speed when the processor can't run at that speed.
That is what I want someone to explain because it makes no sense to me and would like someone to clarify it.

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