[kupan787]

Ok, if both these machines existed, which would run "faster" (and which would you rather have):

a) 1GHz (single proc) on a 133 MHz bus with SDRAM, 256k L2, 2 MB L3 (1/4 speed) (basicly Apples current line config)

or

b) 400 MHz (single proc) on a 400 MHz bus with RAMBUS (or DDR), 1 MB L2 cache, No L3 cache

Assume that both are with the G4 7455 (or which ever 74xx was best), so basicly we have virtually identical mahcines except for MHz rating, cache differeces, and the system bus speeds.

Would the speed difference be that much of a difference one way or the other, or would they be close to the same speed. Does bus speed and cahce make that much of a difference?

Thanks,
Ben

[Fyre4ce]

First of all, Apple's current line has DDR L3 cache, so it effectively runs at half the processor speed, not 25%.

The 1 GHz processor would clearly be faster. Even if the 400 MHz CPU had an infinitely fast bus (in other words, it made maximal use of every CPU clock tick) it still would not be as fast as the 1 GHz.

However, the current lineup NEEDS faster busses. The speed difference between a 133 MHz bus and a 166 MHz DDR bus would be incredible.

[Commodus]

Look at it this way: you can have a six-lane highway, but if you only ever get enough traffic to fill two lanes, there's no point to having much (if anything) more. There's a balance that has to be struck, but bus speed will only take you so far.

[Blake Bowden]

According to Apple the 400mhz and the 1GHZ *should* run the same as people thinking the 1GHZ is faster are falling for the MHZ myth J/K. Of course the 1GHZ would be faster. Now if was a 800 instead of 400, in some applications the 800 would probably outperform the 1GHZ.

[siegzdad]

Originally posted by Fyre4ce:
[QB]First of all, Apple's current line has DDR L3 cache, so it effectively runs at half the processor speed, not 25%.
[QB]

Sorry to dissapoint you, but according to http://docs.info.apple.com/article.html?artnum=43106 the L3 cache only runs at 1/4 processor speed.

[Cipher13]

Originally posted by siegzdad:
<STRONG>

Sorry to dissapoint you, but according to http://docs.info.apple.com/article.html?artnum=43106 the L3 cache only runs at 1/4 processor speed.</STRONG>

Fyre4ce is saying because its DDR it can push twice as much as a non-DDR cache.

The GHz machine would be faster. While the 400 MHz machine on a 400 MHz bus MAY be faster than a 400 MHz machine on a 133 MHz bus, the difference would be negligible.

The GHz machine would come much closer to maxing out the bus. It's all a matter of need... if the 400 MHz machine doesn't utilise at least 100% of the 133 MHz bus, then it won't benefit noticeably from a 400 MHz bus.

[Dan Szwarc]

Don't be fooled by the 400MHz bus speed in Rambus ram. It doesn't have the same bit-width as SDRAM and therefore isn't 3X faster as 133MHz SDRAM (insert highway analogy here).

It's probably closer to 200MHz on a MB/s comparison, but I don't have any specifics in front of me.

Anyone? Anyone? Bueler?

[Fyre4ce]

The best way to look at "bus speed" is to analyze the speed of the RAM (the main thing that communicates with the CPU). Here are the maxumum throughputs of common types of RAM found today:

(clock speed, SDR/DDR, bandwidth)

PC100 SDRAM: 800 MB/s (100 MHz, SDR, 64 bits)
PC133 SDRAM: 1067 MB/s (133 MHz, SDR, 64 bits) &lt;--- APPLE IS HERE
PC150 SDRAM: 1200 MB/s (150 MHz, SDR, 64 bits)
PC600 RDRAM: 1200 MB/s (300 MHz, DDR, 16 bits)
PC700 RDRAM: 1400 MB/s (350 MHz, DDR, 16 bits)
PC800 RDRAM: 1600 MB/s (400 MHz, DDR, 16 bits) &lt;--- INTEL IS HERE
PC1600 DDR SDRAM: 1600 MB/s (100 MHz, DDR, 64 bits)
PC2100 DDR SDRAM: 2133 MB/s (133 MHz, DDR, 64 bits) &lt;--- AMD IS HERE
PC2400 DDR SDRAM: 2400 MB/s (150 MHz, DDR, 64 bits)
PC2700 DDR SDRAM: 2667 MB/s (167 MHz, DDR, 64 bits)

Heh, we suck. I'm hoping for at least PC2100 RAM in the next Power Macs, hopefully PC2700. If Apple's current Power Macs ran on some serious RAM, (a) they would be MUCH faster, and (b) there would be one on my desk.

[Turbocharger]

Read this for a comparison of these memory technologies:
http://www.aceshardware.com/read.jsp?id=45000300

[Drenn]

This reply is for the posing that FYRE4CE left. I have copied it below in Bold.

What you have here is true in the way of spec and what I'm about to say is debatible by most but I think you must be one of the people that beleive if it says 1GHz it's faster than anything below it no matter what machine your talking about. For instance a G4 800Mhz. Is it slower then a 1GHz intel box........No its not slower. The G4 800MHZ will blow the 1GHZ doors off rendering graphics and thats where the true show of power is.. The fact is all these machines are designed differently and just because it says its a 1GHz or 2Ghz or whatever dosn't mean it's better or faster then the other brands that have there machines labled as being 400 or 600MHZ. In some cases with certain peices of softwear however some machines will load faster then others this has to do with how the software is writen and what it is told to utilize. I'm starting to get off the subject slightly but I think you see what I'm saying. Oh by the way....I would want the G4 1Ghz


The best way to look at "bus speed" is to analyze the speed of the RAM (the main thing that communicates with the CPU). Here are the maxumum throughputs of common types of RAM found today:

(clock speed, SDR/DDR, bandwidth)

PC100 SDRAM: 800 MB/s (100 MHz, SDR, 64 bits)
PC133 SDRAM: 1067 MB/s (133 MHz, SDR, 64 bits) &lt;--- APPLE IS HERE
PC150 SDRAM: 1200 MB/s (150 MHz, SDR, 64 bits)
PC600 RDRAM: 1200 MB/s (300 MHz, DDR, 16 bits)
PC700 RDRAM: 1400 MB/s (350 MHz, DDR, 16 bits)
PC800 RDRAM: 1600 MB/s (400 MHz, DDR, 16 bits) &lt;--- INTEL IS HERE
PC1600 DDR SDRAM: 1600 MB/s (100 MHz, DDR, 64 bits)
PC2100 DDR SDRAM: 2133 MB/s (133 MHz, DDR, 64 bits) &lt;--- AMD IS HERE
PC2400 DDR SDRAM: 2400 MB/s (150 MHz, DDR, 64 bits)
PC2700 DDR SDRAM: 2667 MB/s (167 MHz, DDR, 64 bits)

Heh, we suck. I'm hoping for at least PC2100 RAM in the next Power Macs, hopefully PC2700. If Apple's current Power Macs ran on some serious RAM, (a) they would be MUCH faster, and (b) there would be one on my desk.

________________

Fyre4ce[/LIST]