Running 266MHz FSB with PC100 RAM?

[DragonQ0105]

Yo! PC works....whooooptidoooo!

Now I have my Main Computer back, and my shiny new AthlonXP 3200+ Downstairs...hehehe...

Anyway, this new CPU is an AMD Athlon 2000+ (266MHz FSB).
However, I only have PC100 SDRAM.

At the moment I'm running my CPU at 200MHz FSB (so it is running at 1.25GHz instead of 1.67GHz), but I'd like to run it at full speed. Can I run my Processor at 266MHz FSB (133MHz DDR), and my PC100 SDRAM staying at 200MHz (100MHz DDR)? Will this cause stability problems?

 

[ceh4702]

The kind of RAM you can use is dictated by your motherboard. Most AMD motherboards use DDR. Some older motherboards are limited to PC2100 (DDR266) or PC2700 (DDR333). The current Athlon XP processor motherboards use PC3200 (DDR400). Sometimes slightly faster RAM like PC3500 might be used for overclocking or for lower latency settings.

Your motherboard may default to an FSB of 200mhz because it can also run DURON CPU's. When Athlons first came out some of the original Athlons could have run at an FSB of either 200Mhz or 266Mhz, Depending on the CPU model.

Sometimes people use DDR400 with a CPU that has an FSB of 333Mhz like the AMD XP2500 CPU. I think they set the speed to "BY SPD" For the RAM.

RAM that has a rate Slower than the CPU's FSB may slow down a processor.

It is kind of wierd when they use the term DDR SDRAM. Is it DDR or SDRAM?

If you do not like my post feel free to point out your opinion or my errors.

 

[DragonQ0105]

My Motherboard is an MSI KM2M Combo-L, and has slots for DDR and SDR SDRAM.

SDRAM means Synchronous Dynamic Random Access Memory.

DDR SDRAM is still Synchronous Dynamic Random Access Memory, but it has Double Data Rate.

SDR SDRAM is the older type Single Data Rate Synchronous Dynamic Random Access Memory.

That's why people use the term "DDR SDRAM". When people just say "SDRAM", they are refering to "SDR SDRAM".


Anyway, back to my question, I know it'll mean the SDRAM won't be able to keep up with the processor, but is it still worth putting the CPU's FSB to 266MHz and leaving the RAM timing at 100Mhz?

 

[cdogg]

DragonQ,

No, it will not work. The motherboard is not capable of running both DDR and regular SDRAM at the same time. Also, you do not want to adjust the system bus any higher than 100MHz while you have PC100 SDRAM in the system. Doing so will likely ruin those DIMMs if you go too high.

Remember, the frontside bus is separate from the memory bus. Both depend on the [blue]system bus[/blue] which is what you can adjust in the BIOS. The CPU you have uses a 2x multiplier for the frontside bus. That's why a 100MHz system bus allows the frontside bus to run at 200MHz.

The same goes for memory. Once you get your hands on PC2100 DDR (266MHz), then you can set the system bus to 133MHz (usually automatic once you insert the memory) giving both the frontside and memory busses the ability to run at 266MHz.

That's a pretty technical explanation, but if any of it's not clear let me know...


~cdogg
[tab]"All paid jobs absorb and degrade the mind";
[tab][tab]- Aristotle
[tab][navy]For general rules and guidelines to get better answers, click here:[/navy] faq219-2884

 

[Lemon13]

if you board can handle async. cpu/ram freq. yes, you def. will gain more by setting the cpu to 133fsb then you loose because of the asyn. freq.
(a lot people say its not worth it, but hey, i tried on one system of mine and it gained of it!)

 

[cdogg]

Lemon's right. Some BIOS's give you the ability to set asynchronous frequencies between the CPU and RAM. It would then be possible for you to increase your FSB to the needed 266MHz (133MHz x 2) while leaving your memory bus at 100MHz.

It's definitely worth it in this situation if you have that option, because it will boost your CPU speed from 1.25 to 1.67GHz.

The argument about not using asynchronous speeds is when you are changing it to accomodate memory (not the FSB like in this situation). Sometimes the small bump to memory hurts overall performance because of the "latency" factor. Although there will be one in this situation, the BIG jump in CPU speed is more beneficial and easily overrides any hit from latency.


~cdogg
[tab]"All paid jobs absorb and degrade the mind";
[tab][tab]- Aristotle
[tab][navy]For general rules and guidelines to get better answers, click here:[/navy] faq219-2884

 

[DragonQ0105]

Yeah in the BIOS, I can set RAM and CPU Bus Settings separately....so it's worth doing...good...