How does the PC core work??


Dec 24, 2002
I'm gonna buy a system and have planned for the following trio:
D845PESV mobo at 400/533Mhz FSB and support for DDR 333Mhz,
P4 2.0Ghz cpu at 400Mhz FSB,
and 256MB PC2700 DDR memory at 333Mhz.

Thing is, I thought the above all work perfect with each other... But someone told me that the entire core runs only as fast as it's slowest component. Well, to the best of my understaing (read: correct me, correct me), either that's true and the sys will run at core speed of 333Mhz (well, the cpu will run faster by it's multiplier), or if it's not true - the cpu and mobo will communicate at 400mhz but the the cpu-memory communication will be only 333Mhz.

My question is this:
HOW (big letters for expression of frustration) DOES THIS ALL WORK?

It seems as though the specified components are all "meant to be" together, being of the same generation of development and price scale... Is this wrong? Is there something fundemetally wrong with the components compatibility with each other?

If the sys will only run at 333Mhz, should I go for DDR 400Mhz? well, an other mobo is needed then - how about forgeting it all and going with RDRAM PC800??


LOL, Intel's bus is Quad Data Rate, DDR memory is Double Data Rate. The only way you can get them to exactly match is to use DDR400 on a "400" bus CPU, but that board doesn't support such a configuration. Another match is PC800 RDRAM. Why does it match? Each RIMM is 16-bits (not 64 like SDRAM), so a pair of them is 32-bits, and the CPU bus is 64 bits, so since the CPU bus is twice as wide, the PC800 makes up by being twice as fast.

Of course you could get a performance board like the Asus P4T533-C and a pair of PC1066 modules, those match. Or newer technology, RIMM 4200 is a pair of PC1066 modules crammed into one wider module, the Asus P4T533 (without the -C) uses them.

<font color=blue>You're posting in a forum with class. It may be third class, but it's still class!</font color=blue>


Nov 26, 2002
Yo J,

Crashman is totally correct, but this might help you understand a little more:

Your CPU is running on a 100 mhz cpu bus............100 mhz X 20 mobo multiplier = 2000 mhz

Your DDR is running on a 166 mhz memory bus.......... 166 mhz X 2(DDR= double data rate)= 333 mhz

Your Front Side Bus is what most people would call 333 mhz......this is tricky because your real FSB should be your CPU Bus or Memory Bus rate, it is only the Retailers/Marketing people who call it a 333 mhz FSB.

Everything will run fine together.

As of this post, there is not a JEDEC standard for DDR400, so no mobo can officially support it. It will be made a real standard soon, as Intel has made plans to use it for future CPU's & chipsets.

If cost is no object, yes you should go for a 1066 RD-Ram system.

Peace Out................tile2

Why do you want to believe me?