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"megahertz Myth"


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I saw Mr Steve J. explain the so called "Megahertz Myth" in a video today...basically saying why an 800MHz G4 is faster than an 1800MHz P4...

 

Was just curious as to what folks here think of it...and what could be wrong with his explanation.

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As far as I know it all about efficency ie how well the cpu uses each cycle. It would explain why Mac cpus (Motorola I think but not sure) aswell as AMD cpus can run at a lower clock and still perform aswell as an Intel, for example.

 

From what I've seen, an Athlon 2200+ which runs at about 1.5GHz performs nearly identical to an Intel running at 2.2GHz.

 

Correct me if I'm wrong, this is from memory!

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Basically it's a big explanation of Pipelining and how efficient it is/isn't.

 

http://www.esm.psu.edu/Faculty/Gray/movies.html is the site with all the links.

 

Direct download for Megahertz Myth Video:

http://www.esm.psu.edu/Faculty/Gray/graphi...z_myth_320f.mov (17MB)

Edited by bacterozoid
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the 800 meg g4s can't keep up w/ a 1.8 p4, i've used the g4's exstensively. now the dually g4 units, thoose would blow the hell out of the 1.8 gig unit, which is probably what he's talking about.

 

but for the 800 meg unit to overcome the 1.8 unit, the g4 would need to do double the calculations and include to extra pipelines to beat the 1.8

 

amd doesn't even double the calcs. it's like 5/intel 9/amd or something like that....

 

intresting vid though.... they only used execution of a very simple code to show the results. i'm going to be willing to bet though that in critical data execution that longer pipe would be better to have as more units are handling smaller portions of the code. not sure though.

 

how come they don't show amd in it? or would it be because thoose units all do the relative same number of work per clock?

 

EDIT>> it's nearly 900 megz g4 and a 1.7 p4. so it's kinda like comparing the 733 p3 to a 1.2 p4.

Edited by wdeydwondrer
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As far as I know it all about efficency ie how well the cpu uses each cycle. It would explain why Mac cpus (Motorola I think but not sure) aswell as AMD cpus can run at a lower clock and still perform aswell as an Intel, for example.

 

From what I've seen, an Athlon 2200+ which runs at about 1.5GHz performs nearly identical to an Intel running at 2.2GHz.

 

Correct me if I'm wrong, this is from memory!

Similar, but not always that close. I benched my computer against my friends, are setups were almost the same except he had a AMD 3200+ against my P4 3.0C. We ran a bunch of benchmarks against eachother and honestly my computer schooled his. Not to say all comparisons go the same way, but my computer beat his in all but 1 category in PCMARK, and are systems are very similar with the exception of the processor.
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amd doesn't even double the calcs. it's like 5/intel 9/amd or something like that....

yea that's it :)

something to do with that explains why, i guess.

 

also, a 2200+ runs at 1.8 GHz, the sempron might run at 1.5 GHz though (which would be an 1800+ because AMD screwed them up, and they perform the same as an athlon xp, comparing clock to clock speed).

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yea that's it :)

something to do with that explains why, i guess.

 

also, a 2200+ runs at 1.8 GHz, the sempron might run at 1.5 GHz though (which would be an 1800+ because AMD screwed them up, and they perform the same as an athlon xp, comparing clock to clock speed).

The Sempron is the AthlonXP.
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Not quite.

The semprons are cheaper for clock to clock speed (meaning either way, they are cheaper), and all of them besides the 3100+ (and maybe the 2800+) have a t-bred core.

the athlon XPs have a barton core, older ones have a t-bred.

The semprons run at different speeds for their PRs (2800+ 2 GHz, vs. the XP, 2800+ 2.25 GHz).

 

Then you could say it's the same thing as a duron (with extra L2 cache), athlon, and athlon MP (without the MP support, of course).

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Not quite.

The semprons are cheaper for clock to clock speed (meaning either way, they are cheaper), and all of them besides the 3100+ (and maybe the 2800+) have a t-bred core.

the athlon XPs have a barton core, older ones have a t-bred.

The semprons run at different speeds for their PRs (2800+ 2 GHz, vs. the XP, 2800+ 2.25 GHz).

 

Then you could say it's the same thing as a duron (with extra L2 cache), athlon, and athlon MP (without the MP support, of course).

the sempron replaced the xp line for socket a. I know the bartons are better but they stopped makin them. Edited by wsrider
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Actually, it's been proven that a Dual G5 2.5Ghz Mac is about as fast as a dual Opteron 2.4Ghz rig.

 

They said the Mac was cheaper, but the Opteron rig was built by Alienware. Go figure... Mac fanatics will do anything to make Macs look good, even if it means comparing apples to oranges.

 

The Mac was a little faster at I/o operations, such as HD intensive things, but the Opterons own3d it in everything else.

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Well as far as I know the Semprons are the new Durons, AMD wanted to give them a new face.

 

About the cores being the same, I think thats right from what I've seen. I had my 1.2 TBird running @ 1.4GHz and I've got this Sempron 2200+ @ 1.4Ghz and the Sempron is well faster, even though it is underclocked. According to the AMD website, the Sempron 2200+ runs at 1.5GHz.

 

And I couldn't play Doom3 or run 3DMark05 on the TBird, but I can now...

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I believe it to be true. Just like AMD does it, MHZ, or GHZ, mean nothing, I mean, they do, but you get the point. :P Intel's Mobile Processors, like the Centrino do not have high clocks, but lots of L2 (they don't have L3's, do they?)... which are 2 megs.

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the sempron replaced the xp line for socket a. I know the bartons are better but they stopped makin them.

brandon said that the sempron IS the athlon xp, which is not true.

What you said is true though.

Mainly, AMD made it as an economic line, but since the athlon xps aren't going anywhere, the semprons came in as a replacement.

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simply because they're cheaper. they really shouldn't be replacing the xp as it's almost a step back in the line of advancement.

 

my opinion, the sempron was just a desperation shot thrown together at the last second to try and boost sales agasint the intel mobile units coming out.

 

they prolly also had a but load of cores and chips that didn't pass quality to ship as the xp units.

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simply because they're cheaper. they really shouldn't be replacing the xp as it's almost a step back in the line of advancement.

 

my opinion, the sempron was just a desperation shot thrown together at the last second to try and boost sales agasint the intel mobile units coming out.

 

they prolly also had a but load of cores and chips that didn't pass quality to ship as the xp units.

they released the sempron as a budget socket a and socket 754 chip. They couldnt keep selling the highend xp's 3000+ 3200+ at the price they where cause of there k8 chips filling in that market so they cut the xp line and reintroduced them as semprons there basicly tbreds. They can sell these much cheaper for socket a then they did with the xp's (bartons).
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they aren't re-introduced xp units, they are totally different. they're constructed as a cross between an xp and a duron.

 

the price difference is almost negligable, all of them hoovering right between 80-200 bux. that's HARDLY enough reason to delete an entire line just because cost alone.

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i think the semprons perform the same as the t-bred core, so a 2ghz sempron is very close to a 2ghz axp. They change the ratings higher to match the celeron speed, instead of p4. Isnt this what they did, did you notice desktop chips got reduced to 55W.

Yep, that's exactly right.

That explains the PR difference too. Celerons are crap in general, well at least the northwood and willamette ones are. I saw a 2.2 GHz northwood outperforming a 2.6 GHz northwood, and the 2, 2.2, 2.4, and 2.6 GHz northwoods were performing at around the same performance.

All semprons besides the 3100+ have a t-bred core, so they will perform close to an athlon xp for clock to clock speed.

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