CPU structure 43 replies

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Greenvalv

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#1 12 years ago

I don't fully understand how L1 and L2 cache work, could someone explain to me in simplistic terms what they do exactly? This didn't help much: http://en.wikipedia.org/wiki/L1_cache This part helped me understand FSB: http://en.wikipedia.org/wiki/Front_side_bus Athlon's tend to have slower core clocks but are faster than Pentiums, how come? And is HT on AMD's the same as FSB on Intel's? I'm deciding between the Pentium D here and the Athlon 64 here. Better understanding of the basic parts will help.




Hmmmdonut

The real Homer

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6th July 2005

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#2 12 years ago

G®33N<@|>I don't fully understand how L1 and L2 cache work, could someone explain to me in simplistic terms what they do exactly? This didn't help much: http://en.wikipedia.org/wiki/L1_cache This part helped me understand FSB: http://en.wikipedia.org/wiki/Front_side_bus

Athlon's tend to have slower core clocks but are faster than Pentiums, how come? And is HT on AMD's the same as FSB on Intel's?

I'm deciding between the Pentium D here and the Athlon 64 here. Better understanding of the basic parts will help.

A64's are faster because they do more work per clock. I believe A64's can handle 6 instuctions per clock while Netburst can only handle 4.

L1 and L2 cache are just super fast storage. The amount of cache needed is dependent on the arch. A64's do not need a lot of cache because they are not bandwith starved like Netburst.

http://arstechnica.com/articles/paedia/cpu/caching.ars http://arstechnica.com/articles/paedia/cpu/amd-hammer-1.ars/9 http://www.cpuid.com/reviews/K8/index.php




deathwarder

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#3 12 years ago

if you want the full explination then here it goes, your main memory does not work as fast as your cpu, so it would slow the cpu down if the cpu didnt have its own memory, so the L1 cache is the innermost memory, right in the center of the die usually, and it is where the cpu store instructions and data to be used, the L2 cache is an extension of this which precaches data and can make requests for data for the cpu, to be moved into the L1 cache later, the advantage of the L1 is that it has an incredibly low latency and short distance to the cpu, same but less so for L2, the other thing is that they both work at the cpu's clock speed, making memory requests really really fast. A64's do more work per clock, you see, there is what is called an instruction pipeline in the cpu, for the athlon it is around 10-13 stages, for the intel p4 it is about 17-20, this means that if there is any idle time at all, and there is always some time, even during 100%, bubbles start to form, unused clock cycles that must go through the whole pipeline, so for amd's much less is lost than p4's, the p4 has a long pipeline for more specialized instruction sets per clock




C38368

...burning angel wings to dust

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#4 12 years ago

Not quite correct about pipeline length and its effects: each stage of a pipeline does something, and when taken as a whole each stage of the pipeline build up to produce one operation. The number of stages in a pipeline determine how much each stage needs to do. To oversimplify it, in a 20-stage pipeline each stage needs to do, on average, one-twentieth of the work to complete one operation. This is necessary to achieve high clock speeds, and the primary reason that AMD clocks their chips lower than Intel (anyone else aware of the fact that the Core architecture has a shorter pipeline than P4 to go along with its lower clock speeds?). The downside is that a long pipeline takes longer to fill and--more importantly--longer to flush. Thus, a branch misprediction in a long-pipe architecture is far more damaging to performance than on a short-pipe architecture.

Both replies also missed the bit about AMD having a disturbingly efficient memory controller built into the CPU die; this alone made for a huge performance advantage, and is a large part of the reason why even with DDR2 Intel chips took so long to overcome AMD's advantage in that area.

And death... I didn't read your profile.




deathwarder

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#5 12 years ago

run it through a binary tanslator, but anyway, also, the way the xbox360 has 3 3.0ghz cores on one chip is a 2stage pipeline(or is it one?)




C38368

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#6 12 years ago
deathwarderrun it through a binary tanslator, but anyway, also, the way the xbox360 has 3 3.0ghz cores on one chip is a 2stage pipeline(or is it one?)

What are you on about? Pipelines exist inside a core, as it were. The number of cores in a package has no bearing on the number of stages in a pipeline.

And I can convert to and from binary manually, thankyouverymuch.




Greenvalv

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#7 12 years ago

So, for internet browsing and CD burning, which would be better?




Bs|Archaon

I would die without GF

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#8 12 years ago

For that kind of low-power task they're so unbelievably close that I'd say it's not worth worrying about; pay more attention to things like price and motherboard features, then just buy whatever CPU it takes. If you're going to use it for anything more demanding, then yes, give it some thought; but for literally just browsing and burning it doesn't matter. Unless by CD Burning you include things like converting audio/video, in which case I'd go for Intel as they are usually faster than AMD for that kind of thing.




Greenvalv

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#9 12 years ago

Would this fan (http://www.newegg.com/product/product.asp?item=N82E16835114036) still work with the 805 Pentium D? It says it only supports 630 / 640 /650 / 520 / 520j / 530 / 530j / 540 / 540j / 550j




C38368

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#10 12 years ago
G®33N<@|>Would this fan (http://www.newegg.com/product/product.asp?item=N82E16835114036) still work with the 805 Pentium D? It says it only supports 630 / 640 /650 / 520 / 520j / 530 / 530j / 540 / 540j / 550j

Why would you buy that in the first place? It's intended to cool CPUs in a 1U server case (note the horizontal flow pattern); you can do better for a desktop at comparable cost.