Can someone explain how RAM limits CPU speeds?

[RedScare]

ok thank you. that cleared it up a little bit for me. couple follow up questions though...

- so, if i am running pc2100 ram, in single channel mode, upping the fsb past 133 wont do anything to help performance right? since thats the fastest the memory can operate correct?

- a question about these mobile bartons which are so popular now...from what i understand, they are incredibly easy to overclock because they are unlocked and all you have to do is up the multiplier. have i understood that correctly? so if the fsb is 266 for a 2600+, it normally has a multi of 7.5 to bring operating frequency up to 2.0GHz right? but then you can just increase the multi, and bring the operating frequency up further without changing the fsb (keeping it at 133)? or did i miss something. im not exactly sure i understand how simply upping the operating frequency by changing the multi will help anything, since i would think my ram would still be the rate limiting factor. i think im missing something here...

and thanks for the help guys, i realize these questions probably sound really dumb to you but thanks for helping a noob out

 

[Sahakiel]

Originally posted by: redscare05
ok thank you. that cleared it up a little bit for me. couple follow up questions though...

- so, if i am running pc2100 ram, in single channel mode, upping the fsb past 133 wont do anything to help performance right? since thats the fastest the memory can operate correct?

In theory, it might give a bit of a boost. I'm not too familiar with the EV8 bus to know how much.
In practice, it probably would be negligible and may actually be detrimental to performance depending on the hardware design.

- a question about these mobile bartons which are so popular now...from what i understand, they are incredibly easy to overclock because they are unlocked and all you have to do is up the multiplier. have i understood that correctly?

I'm not too familiar with how bartons are doing since I haven't had time to do much research.
However, I do know that how much those chips can overclock is really a byproduct of binning. It's a marketing term, but suffice to say it has nothing to do with the multiplier. The unlocked multiplier simply makes it easier by removing your memory as a limiting factor.

so if the fsb is 266 for a 2600+, it normally has a multi of 7.5 to bring operating frequency up to 2.0GHz right?

That's not quite true. The 266 number comes from a doubling of the data rate per clock cycle. Athlon chips use similar DDR technology as your memory so the FSB is actually running at 133MHz. The multiplier for 2 GHz operation is 15.

but then you can just increase the multi, and bring the operating frequency up further without changing the fsb (keeping it at 133)? or did i miss something. im not exactly sure i understand how simply upping the operating frequency by changing the multi will help anything, since i would think my ram would still be the rate limiting factor. i think im missing something here...

Yes, you can simply increase the multiplier and the CPU frequency will scale accordingly while keeping your memory at 133 MHz. However, your performance gain will be less than if you had also increased both your FSB and memory speeds. Long story short, each program has a different memory/CPU profile; some use more CPU time, some use more memory bandwidth. Increasing the multiplier only will increase CPU performance, which will increase system performance overall, but for programs that were already limited by memory speed, it won't help as much.

 

[RedScare]

ok that makes sense. thanks. so basically, it would be a good idea to get some DDR400 RAM so that i could theoretically increase the fsb up to at least 200 without running into any problems with the memory lagging behind the cpu?

thanks again for the help. i think im starting to understand all this stuff

 

[RobCur]

just get xp2600 266 fsb not 333fsb, althought 333fsb will perform a little better but your pc2100 will limit you to 266fsb. dont be confused, because you cannot run your cpu at 333 fsb while keeping your pc2100 at 266fsb, it just theoritically speaking impossible. althought you can run your cpu at 266 and your memory at 333FSB but not the other way around because cpu are more starved then your memory and no motherboard is design in a way as to run your memory slower then your cpu in terms of FSB.
also you would get a bigger boost going from 100 to 133, then 133 to 166. heh.
if you want 333FSB processor then trash your pc2100 and get pc2700 LOL which imho ain't worth it at all, because memory prices have increases expotenially as well. pc2700 only cost a little more then pc2100, not a big deal.

 

[CHarrington]

If you have the money, do the following:

Buy a mobile 2600.

Buy two 256MB (or 512MB if you have the money) sticks of RAM from OCZ, Mushkin, Geil, or Corsair.

Buy either the NF7-S mobo or a DFI mobo.

This upgrade will blow your old rig out of the water, even before overclocking.

If you do plan to overclock (as anyone with your new setup would) get a performance heatsink and fan.

Once you have the upgraded HSF try setting your core voltage to 1.80, your multiplyer to 12.5, and your FSB to 200mhz. If you have no problems running UT2K4, try lowering your core voltage - then repeat. Once you have problems, put your core voltage back up to whatever voltage was stable.

This is by no means the limit. However, this is a very solid foundation to build upon.

Good luck!

 

[Soulkeeper]

1.8v is too high
be carefull with the vcore and bios settings

 

[RedScare]

well, i dont have the money to buy the ram at the moment (id want two sticks of 512 which would run me at least an extra 200 bucks which i am not prepared to spend right now)

but i will buy the nf7 or the dfi ultra infinity board. i will just run the memory in single channel for the time being and ill run the mobile 2600 (266fsb) at its rated frequency with my pc2100 ram. then, if i feel like im not getting the performance i want, ill just have to upgrade my memory. everything else will be ready to go and ill work on overclocking the cpu. sound like a plan? i think i have this figured out finally thanks!

 

[L00PY]

My mobo runs in dual channel mode fine with one 512 MB stick (some generic stuff) and two 256MB sticks (matching Crucial) -- it depends on the mobo. You can try throwing a third stick of in and seeing if it works on yours too.

 

[niall]

For best stability, yes, you're much better off running your CPU and memory at the same MHz rating. In this case, the 2600+ Mobile Barton is rated 266, and 2100 memory is also rated 266, so all you'd need to do is run single-channel mode since your two memory sticks are not absolutely identical. Eventually, you could replace the 256k with a 266MHz 512k, but you'd have to make sure it has all the same ratings as the current one for dual-channel to work without a hitch (and without the knowledge to play with things in the BIOS).

This would limit a little what your motherboard can do, though, as both the NF7 and DFI-I are 400MHz FSB boards. It all depends how many more upgrades you intend to do on it; if within a year or so you feel you can afford 400MHZ CPU and memory, then the boards are a good future investment. Otherwise maybe even a slightly older 266MHz board might do the trick; the CPU upgrade alone will make an improvement in gaming capability.

I suggest reading more on reviews and benchmarks, especially older ones that might pit thunderbirds against XPs, to see what kind of improvement you'd get. AnandTech has a good selection to start with, if you go in the CPU section and look at old articles.

I'm not exactly a noob myself, but I can understand feeling like one with all the recent changes and choices available, and the hoops one has to go through to make sure that parts bought seperately manage to work together. Which for just about everyone here, is the biggest fun of all, I think. Good luck!

EDIT: Upon re-reading, I think I may have some incorrect information, so take a grain of salt with this. I'm quite sure someone will point out my errors very soon anyways.