Confused.....again!

[ComputerNut]

Alright, i want to upgrade the ram on that celeron system I built awhile ago. the mobo is an ASUS P4S533-MX, therefore it has combo DDR + SDR. the cpu has an FSB of 400. Will pc2700 (ddr333) work on this?

Sry if this question sounds rather stupid. its been awhile since ive had to deal with fsb's and ram speeds.

EDIT: Well my first double post.....peak hours can sure mess me up!

[mattbell]

DDR 333 will work but your prob best getting DDR 400 that way it matches the speed of your FSB.

Matt

[RJ]

No, that's not the way it works.
DDR is double pumped, the P4 is quad pumped. So the FSB of 400 runs at 100 MHz and DDR200 runs at 100 MHz too.

Means that DDR200 is the RAM that matches the FSB speed.

DDR333 will work too, but will work at DDR200 speed to match the FSB.

RJ

[ric449]

Actually, if you use DDR 333 in a celeron system with a 400MHz FSB, the memory will downclock to DDR 266. If you run 2 sticks of memory in dual channel configuration, then both sticks would downclock to DDR 200.

[Cricket]

Originally posted by ric449 Actually, if you use DDR 333 in a celeron system with a 400MHz FSB, the memory will downclock to DDR 266.

Did you mean to type DDR200?

Cricket

[ric449]

No, I actually mean the memory will downclock to DDR 266. I am running a celeron with 400MHz FSB now, and here is a screen shot from CPU-Z on the memory tab. Also, if you look on intel it shows that with the 400MHz FSB DDR266 is used. It is only when using dual channel the memory will downclock to DDR200.

[Cricket]

Originally posted by ric449 No, I actually mean the memory will downclock to DDR 266. I am running a celeron with 400MHz FSB now, and here is a screen shot from CPU-Z on the memory tab. Also, if you look on intel it shows that with the 400MHz FSB DDR266 is used. It is only when using dual channel the memory will downclock to DDR200.

I think it would depend on the motherboard in use and whether it can run the RAM and CPU asymmetrical or not. Celerons run on the 100MHz motherboard FSB and if the CPU and RAM can't be run asymmetrical, the RAM will run like PC1600 (DDR200) because it has to run on the 100MHz FSB. But if the motherboard can run the CPU and RAM out of synch then I'm surprised the RAM doesn't run at PC2700 (DDR333) speeds.

Cricket

[ric449]

It's just the way things are. You need to bear in mind that when the 400MHz FSB was introduced, there wasn't any DDR333. Like Intel say, the only way you can get full performance from one of their systems is with dual channel mode. Here is the memory requirements for single channel setups:

400MHz FSB- DDR266
533MHz FSB- DDR333
800MHz FSB- DDR400

Dual channel setups:

400MHz FSB- DDR200
533MHz FSB- DDR266
800MHz FSB- DDR400

I got this info from Intel and Upgrading and repairing PC's 15th edition, from Scott Mueller.

[Redfallon]

Originally posted by Cricket I think it would depend on the motherboard in use and whether it can run the RAM and CPU asymmetrical or not. Celerons run on the 100MHz motherboard FSB and if the CPU and RAM can't be run asymmetrical, the RAM will run like PC1600 (DDR200) because it has to run on the 100MHz FSB. But if the motherboard can run the CPU and RAM out of synch then I'm surprised the RAM doesn't run at PC2700 (DDR333) speeds. Cricket

I think the most a motherboard will run the RAM at (when talking about running it faster than the front side bus) is like a 4:5 divider, as opposed to a 3:2 or 5:4 when you're slowing the RAM down. I would assume that's why it's not running at full speed (2700), but still faster than the FSB....may be incorrect on this, but I've never seen RAM running faster than a 4:5...

[glc]

That motherboard is not a dual channel board, it's a SiS 651 chipset. You can put DDR333 (PC2700) memory in it, and it will run as fast as the chipset allows. Just let the bios set it up automatically and it will run just fine, further manual tweaking, if even possible, won't gain you much.

[ric449]

Ah, we are not talking Intel here. A ll I know is Intel, since they have the best chipsets. Anyone have a link where I can bring myself up to speed on SiS chipsets?

[BARNEY]

SIS 655 was/is quite formidable with 533 FSB chip - although long in the tooth now is still quite fast.

[glc]

Maybe so, but the SiS 651 is a budget chipset.

[BARNEY]

Yes it is. SIS in general has been and was budget. The 655 though was the fastes for a very short time period during the Intel RDRAM domination. Then came 865PE, 875P, 865G.