# CPU FSB vs RAM speed benchmarks?

## MikePikeFL

Since this is a hardware issue, as well as a speed issue (which many of us Gentoo users are interested in) I thought I'd pose this question here.

I have been unable to find with Google an answer to my dilemma, and I'm not surprised since it's very specific. I also don't want to just go ahead and try it out because of all the labor and risk to my hardware that is involved (pulling everything apart, switching MoBos, CPU coolers.. etc).

So I have the opportunity to take my AthlonXP Thorton (also called thornton?) core 2.0GHz @ 266MHz FSB with 1GB of PC2100 RAM into a motherboard with 1GB of PC2700 RAM. It'd basically be the same system, but instead of the CPU and RAM FSBs running at 266MHz each, the RAM would run at an increased rate. Going from RAM with 2.1GBps to 2.7GBps of bandwidth is almost a 30% increase. The CPU would obviously still be at 266MHz FSB.

Is it worth it? Would I see any increase in performance? Compiling? Doom3?

If anyone knows, or knows of benchmarks that address these issues, please help me out! I've searched around on AnandTech as well as TomsHardware to no avail.

Thanks!

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## NeddySeagoon

MikePikeFL,

For most applications, its not worth it.

A computer is like a set of 'water tanks' connected with pipes of various 'sizes'. The size of the pipe is measured in Mb/sec, which is the data rate that is sustained by the various pipes.

For example, the data rate of the pipe connecting the HDD to main memory is about 50Mb/s. Main memory to CPU is say, 2.1 Gb/s.

The PCI bus is 133Mb/s (for all periperials).

By changing the sizes of these pipes (which is what you want to do) bottlenecks get moved around.

There is another issue for you to consider. Memory and CPU FSB operating syncronously as they do with PC 2100 and FSB 266MHz or asyncronously, if you fit the PC 2700 RAM. Unless the chip set is very carefully designed,  asyncronous RAM/CPU operation can actually lead to a drop in performance.

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## MikePikeFL

 *NeddySeagoon wrote:*   

>  asyncronous RAM/CPU operation can actually lead to a drop in performance.

 

Thanks for the input! I guess this was more or less my question, I couldn't find the right words.   :Cool:   More bandwidth would be great, but would it be offset by asynchro operation. I'm a computer engineer, so I'm well aware of the bottlenecks (my HDD isn't bottlenecking at 50MB/s... I'm running SCSI Raid  :Very Happy:  ) I just wanted to see some real world benchmarks before risking cracking my fragile core... again.

You raise another good point, which may guide me through another round of Googling... 

 *NeddySeagoon wrote:*   

>  Unless the chip set is very carefully designed

 

Perhaps I was searching for the wrong thing, maybe I should look at CHIPSET benchmarks for the new motherboard vs the old...

BTW, for the curious, the two motherboards are:

Epox 8KHA+ w/ VIA KT266A Chipset

Epox 8K9AI w/ VIA KT400 ChipsetLast edited by MikePikeFL on Thu Nov 18, 2004 8:36 pm; edited 1 time in total

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## MikePikeFL

 *NeddySeagoon wrote:*   

> Computer users fall into two groups:-
> 
> those that do backups
> 
> those that have never had a hard drive fail.

 

Love your sig BTW... following my sig, my second favorate quote is:

"Blessed are the pessimists, for they have made backups." -Doug Aiken

I've experienced enough hard drive failues to own my own tape drive and run backups every Friday...    :Rolling Eyes: 

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## NeddySeagoon

MikePikeFL,

Go for it. *Quote:*   

> Epox 8KHA+ w/ VIA KT133A Chipset
> 
> Epox 8K9AI w/ VIA KT400 Chipset

 

The VIA KT133A only supports SDRAM but the VIA KT400 expects DDR. Are you really sure you have PC 2100 DDR in the old motherboard?

I would put the processor you have now in the new motherboard with the new memory and run them both at 266MHz. The memory will be underclocked but there is no harm in that. You could set the memory timing aggressively in teh BIOS.

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## MikePikeFL

 *MikePikeFL wrote:*   

> Epox 8KHA+ w/ VIA KT133A Chipset
> 
> Epox 8K9AI w/ VIA KT400 Chipset

 

Whoops! That should be KT266A! I'll edit that for future reference. Man, KT133A was a while ago...  Sorry about that.

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## NeddySeagoon

MikePikeFL,

The advantages are less clear cut.

If you want to benchmark, you need to use the applications you are going to run.

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## MikePikeFL

 *NeddySeagoon wrote:*   

> If you want to benchmark, you need to use the applications you are going to run.

 

Well, hopefully someone else can point me to an article they may have seen at a site like Anandtech, if they happen to remember such a thing.

Thanks anyway!   :Smile: 

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## MikePikeFL

FWIW, I ran some rudimentary benchmarks myself, just to see. What I did was run a make clean; time make -j2 on 2.6.9 four times for each mem config (this was done on a slackware box).  I changed the mem config in BIOS from autodetect (DDR333) to DDR266. Here are my results. I may run GLXGears next (has a GeForce2MX)... Any other benchmark suggestions?

DDR266:

real 362.48, 363.42, 363.11, 363.20

user 338.56, 339.37, 339.12, 339.34

sys 23.68, 23.80, 23.90, 23.77

DDR333:

real 360.28, 360.83, 361.31, 360.71

user 336.31, 337.04, 337.19, 336.41

sys 23.74, 23.71, 23.72, 23.62

In this case it looks like more bandwidth is slightly better than the latency issues. I stress slightly   :Very Happy: 

PS- I can make the script I wrote to do this available if anyone so desires

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## woZa

Couldn't you just run the cpu at a higer fsb? I'm pretty sure the cpu will do it. Just lower the multiplier (or is the cpu locked?) I'm lucky enough to have an nforce2 board which can access all multipliers...

There are numerous methods of unlocking athlon-xps if you need help with that... Have a look at www.tomshardware.com for some pretty handy guides.

Instead of running 133*15 (which I guess you are running) try 166*12 in the new mobo (keeps the cpu speed the same but ups the fsb and keeps running in sync with the memory).

This will result in quite large speed gains across the board.

Even if the multi is fixed you may be able to up the fsb without the need for raising the cpu voltage. Try it but keep an eye on temps (suggest boot into bios and monitor for 5 mins to make sure things not going crazy.

Eg. I have an XP1700 (default 133*11=1466 I think) running at 200*12=2400 all in sync (had to up vcore to 1.65 though). Even at 200*7 it is way faster than 133*10.5

That's enough waffle anyways!

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## MikePikeFL

 *woZa wrote:*   

> Couldn't you just run the cpu at a higer fsb?

 

Well I've never been big on overclocking... My first Penitum 100 I accidently removed some of the wrong jumpers- poor advice from a friend who high-tailed it after it wouldn't POST and left me with a dead CPU. I like tweaking, but I've had to buy new procs after cracking cores from swapping out heat sinks, and stuff like that. I never have wanted to really increase the risk of having to buy a new CPU.

I've also not had the time to learn the ins and outs of over clocking.

I did however try your suggestion, for the hell of it. The test machine has that Epox board, which allows me to tweak everything, and it's got an AthlonXP 2000+ 1666MHz (133*12.5).

I tried a few settings:

1) FSB 166, Auto, Default Vcore (1.75)

2) FSB 166, 10, Default

3) FSB 166, 10, Vcore 1.8

Each time the system wouldn't post... so I think I'm giving up for now on my first overclocking attempt...

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## woZa

The secret to overclocking is to make each change a small amount and only change one variable at a time...

The idea is to find out what the max fsb your system will run stable at, the max speed your ram will run stable at and then find out the max cpu speed at specific voltages and then combine the three to get a best compromise.

The reason yours wont post at higher fsb is probably because the chipset in the mobo is via based. These don't have pci/agp locks so that when you raise the fsb the pci and agp bus speeds are raised as they are calculated from the fsb speed. The pci bus speed is calculated by (depending on your chipset) 1/3, 1/4, 1/5 etc of the fsb speed. same goes for the agp bus speed (different divider though).

eg fsb=133mhz, pci bus runs at 33mhz. 133/33=4 so the dividor is 1/4.

When you raise the fsb to say 140mhz, the pci bus speed is worked out from the same divider (1/4) so is now running at 35Mhz. The more you overclock the fsb the higher the pci bus speed runs at and this is generally what causes problems. The devices on the pci bus are quite sensitive to these speed increases - especially network & sound cards.

I have been using an nforce2 board for so long that I forgot about this. On nforce2 boards (and maybe some others... I don't know) the pci and agp bus speeds are locked at 33/66mhz regardless of the fsb. This generally makes the pretty decent for overclocking.

Maybe the bios has an agp or pci lock in there somewhere but I doubt it. I used to have an abit kr7a (kt266 based) and could get about 150fsb max. This meant that my pci bus speed was 37.5mhz and agp bus was at 75mhz.

So looks like fsb overclocking is not for you (not to 166 fsb anyway). This is why the nforce2 boards rock (imho!).

You could try increasing the fsb by small amounts (say 3 or 4 mhz at a time but to be honest it's probably not worth it. You might be able to get some joy with increasing the multiplier to get an overclock though. Try it at 0.5 x more than default without changing anything else and see if it posts. If it does check the temps for a while in bios (shouldn't be much higher as it is voltage that increases temps mostly). Then run some cpu intensive apps for a while (15 mis will give you a general idea of stability.) If its ok try another x0.5 increase and so on. When it won't post or crashes during testing it is time to nudges the vcore up A TINY BIT. and try again. This way you will get some free horsepower. 

Downsides to overclocking - temps generally get higher so life expectancy of the hardware being overclocked will decrease. I've been overclocking my xp1700 for 2.5 years and still going strong. Infact the overall voltage needed to keep it at 2400mhz has dropped from 1.75v to 1.65v.

Hope this has given you an insight into overclocking. It's not for everyone but can be a rewarding experience when you get a cpu for £40 and clock it to faster than anything released by amd themselves - all for the price of a decent cpu cooler and some arctic silver (thermal conductive paste)!

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