CPU speed vs. FSB speed

[Krum]

I've just finished building my first computer and I'm trying to tweak the settings to get the fastest speed possible without the machine becoming unstable. I've got the ASUS A7N8X deluxe mobo PCB 2.0, Athlon XP 2400+ 266FSB CPU, and two 512 MB sticks of PC3200 CL 2.5 RAM. The problem is that I can run the CPU at over 2.1 Mhz as long as the FSB is at 133. If I set the FSB at 166 or 200, the computer starts rebooting randomly unless I set the cpu at 2 gig or below. My question is this: is it better to have a slightly lower cpu speed and higher bus speed, or a higher cpu speed and a lower bus speed? I hope I'm being clear here, I'm new this. Thanks!

[Arcuivie]

The FSB is what determines the CPU speed itself, for example, the AMD Athlon XP 2500+ runs at an FSB of 333, you set the FSB in the BIOS to 166, when multiplied by 2 equals 333, which when multiplied by 11 equals 1826 (the processors speed). I wouldn't suggest overclocking unless you have a good HSF.

[Krum]

Thanks for answering, Arcuivie. I understand the connection between FSB and cpu speed, at 133 fsb it's 266 DDR bus speed e.g. when the FSB in the BIOS is 133 the actual speed is 266. I've got the CPU multiplier set at 16.5 with a 133 bus speed giving me an actual CPU clock speed of 2200 mhz (give or take a hertz or two) on a chip designed to run at two gig. My problem is that I'm wondering if the lower bus speed is acting as a choke-point for data, preventing me from fully utilizing my higher cpu speed. My system gets unstable at 166 or 200 fsb when the cpu multiplier is also set to run the chip at 2.2 gigs but is stable at the higher bus speeds at 2 gigs. I'm just wondering if I'd be better off with a bus speed of 133 and a 2.2 gig chip, or a 200 bus speed and a 2 gig chip in terms of overall performance. Maybe this is a dumb question, idunno.

[Krum]

P.S-- Coolermaster copper insert 80mm 6500 RPM heatsink and fan, Arctic silver thermal compound, Xaser III case with seven fans (now I'm broke)

[Gait_Keeper]

Originally posted by Krum
Thanks for answering, Arcuivie. I understand the connection between FSB and cpu speed, at 133 fsb it's 266 DDR bus speed e.g. when the FSB in the BIOS is 133 the actual speed is 266. I've got the CPU multiplier set at 16.5 with a 133 bus speed giving me an actual CPU clock speed of 2200 mhz (give or take a hertz or two) on a chip designed to run at two gig. My problem is that I'm wondering if the lower bus speed is acting as a choke-point for data, preventing me from fully utilizing my higher cpu speed. My system gets unstable at 166 or 200 fsb when the cpu multiplier is also set to run the chip at 2.2 gigs but is stable at the higher bus speeds at 2 gigs. I'm just wondering if I'd be better off with a bus speed of 133 and a 2.2 gig chip, or a 200 bus speed and a 2 gig chip in terms of overall performance. Maybe this is a dumb question, idunno.

good question

[Ultima]

When you run your system at 2.0Ghz/400Mhz it'll be quite a bit faster then when run at 2.2Ghz/266Mhz.

You've got a much larger bandwidth, which results in faster execution of programs and all.

I run my XP1800 Tbred-B at 2.2Ghz/400Mhz stable as a rock, and boy does she fly.
My memory benchmark was pretty good, got about 3000Mb/s with sisoft sandra, here is the link:

http://www.techimo.com/photo/showpho...cat=500&page=1

my scores with a 266Mhz fsb are about 2000Mb/s out of 2100, so that is quite nice, but the main thing to remember is, the higher your fsb, the faster the entire system will be.

[win2kuser]

Another way of looking at it:

11x166fsb = 2.5XP Barton
11x200fsb = 3.2XP!

[JohnE.]

Hi Krum,

Thanks for asking about this... I've been struggling with the very same question(s).

What temps are you getting at those OC speeds? I have the exact same mobo and cpu and just re-applied thermal paste last night. The guy I bought the mobo/cpu/hsf from had put way too much Arctic Silver on it so I carefully replaced it with OCZ Ultra II (using the instructions found here). This dropped the CPU temp from an average 47/48 to an average 44/45 (roughly a 3 degree improvement). Cleaning the dust and grime from the case and front/rear fans and grills dropped the Case temp from 38 to 28

Now that I've lowered the temps somewhat, I'm hoping I can get OC results similar to yours if I can keep the temps in control.

I've got 256MB PC3200 CL 2 ram (much more ram to come when I can afford it) so I'm assuming that it'll still be synchronous with the system bus if I can get the CPU running at 200FSB. Is this correct?

JohnE.

[Krum]

Thanks for the responses, guys. I'm geting cpu temps of 39 C to 42 C when I'm running benchmark tests, with the cpu at 2.2 meg and the fsb at 166, V-core at 1.725 volts. I've got seven damn fans in the case, so it better be cool! The temp goes up to 42.2 at higher clock speeds, but so far those are unstable. These temps are from a hardcano probe attached beneath the cpu so I think I can trust them. I'm still not sure what the highest stable cpu/fsb/memory ratios will be, I had to go to work when I'd rather be at home tweeking my computer. Going to work on it more when I get home tonight

[Krum]

Thanks for all the insights y'all, I appreciate it. I think I'm now stable at 2300mhz, 200 fsb, single 512 stick of Geil mem set at 200 mhz 6-3-3-2.5. My mem bandwith is right at 3000 also, Ultima. I guess the higher CPU speed doesn't translate into improved bandwith. I'd tried to use a generic stick of mem in the second channel on my mobo, but that apparently didn't work out too well.....DOH!!! With just the Geil I seem to be much more stable at higher CPU and FSB speeds. Thanks again!