Understanding clock speed/FSB etc

ray_gillespie

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Hi guys,

Can anyone clear up how the FSB relates to processor and RAM etc clock speeds for me? I'm a bit confused.

My Core 2 Duo E6600 runs at 2.4Ghz, apparently on a 1066Mhz FSB, which I think translates to a multiplier of 9 times the bus speed of 266Mhz. Is that right?

Also, how does this relate to my RAM speed? I have PC2-5300 RAM which runs at 667Mhz - does this mean it's theoretical speed is 333Mhz x 2? How does that fit in with a bus speed of 266Mhz.

Oh, I used to understand all this back in the days of SD-RAM and nice simple 100Mhz buses. Now I'm really confused!!! Please help!!

:)

Thanks.
 

Steevo

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To overclock drop your RAM multiplier and increase your FSB.

These figures are rough, and your exact frequencies will vary due to the clockgenerator and multiplier specifics.

For example 333Mhz RAM has a bootstrap speed of 1/3 the FSB. The FSB will not change if you force a bootstrap speed of say 1/4 the FSB. But the speed of your RAM drops. many boards express this by showing bootstrap speed multiples at stock speeds.


So you may have a RAM speed listing of

266Mhz
300Mhz
333Mhz
366Mhz


etc... and each one will change the bootstrap value of the RAM speed, but not the FSB.


Now if you increase your FSB with the same strap speed on your RAM you will most likely be limited on how much of a overclock you can achieve as the RAM cannot handle the frequency with its default timings, and messing with timings is usally a more advanced user way of overclocking. So for now, dropping your RAM strap speed and changing the FSB is the easiest way to overclock your CPU.
 
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ray_gillespie

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So it's ok to have RAM and CPU buses at different speeds? I always used to think that they had to be the same. Also, what does bootstrap mean?

Please excuse my limited knowledge, that's a very helpful post there Steevo - I just wish I understood it properly! :)
 

Steevo

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Bootstrap is the value in the CMOS that sets the basic system up.

For example it keeps the basic CPU information, voltage, FSB rating, multiplier, etc....


So bootstrap is a term coined years ago, it used to mean to pull one up by ones own bootstraps, which is impossible. But when dealing with a computer, how do you start a execution on hardware that supports so many options, thus the term bootstrap, or boot, or strap is used. But the boot, strap, or power on settings are read from a CMOS chip after the first settings are found, thus making changes possible as CMOS settings are read first.



So when you make changes in the BIOS of a PC it actually records those changes in CMOS (ceramic metal oxide semiconductor) or a combination of a memory chip, a small microcode processor and a mapping unit. This becomes responcible for starting the computer after the initial startup or after the CMOS is cleared.
 

Sazar

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So it's ok to have RAM and CPU buses at different speeds? I always used to think that they had to be the same. Also, what does bootstrap mean?

Please excuse my limited knowledge, that's a very helpful post there Steevo - I just wish I understood it properly! :)

Ratio's are important for overclocking, otherwise you try and run everything at spec (i.e. mem at JEDEC spec, cpu at manufacturer spec) for best stability.

You can do whatever else you want for overclocking, within a degree of variation dependent on thermals, individual components inherent native oc-ability and psu, amongst other things.

What exactly are you looking to do Ray?
 

Steevo

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As Sazar pointed out but I forgot to get into, ratios are important. But more importatnt is stability. Most disk controllers today are offloading the handling of files and RAID calculations so a system that is unstable or makes mistakes in handling data can corrupt data.



Yes it is OK for your ratios to be different, as they will always fall into a corse multiplier of each other as they use a common clock signal to generate each one. If you progress to the point of overclocking and wanting the most out of your system memory timings VS speed, FSB VS temperature, voltage tuning VS cooling and alot of other factors come into play.


My current system outperforms alot of AM and AM2 systems despite being older as I have better memory timings at speed than DDR2 offers. I can push 2.8Ghz but the FSB wall for me is right there and the heat generated is more than I like for the amount of cooling noise generated. Plus then I also loose my tight timings and RAM speed so larger applications suffer and smaller ones benefit.



For a start drop your RAM strap by one setting and up your FSB using a in windows utility by 10Mhz till you get a error running Prime95 1million places and then let it set and run 1million places looped for 4 hours and then 2, 8, and 16 for the same time. If it passes all those then you have a good stable overclock and no risk of damaging your hardware as it will be your memory that limits you.
 

ray_gillespie

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Thanks for the great info guys. I'm not looking to anything at the moment, I just wanted to understand this stuff a bit better. I've not ruled out overclocking in the future, particularly when my CPU begins to look a little dated, so it'll all be useful info for that anyway.

Reps to you all, thanks again.
 

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