Why doesn't Apple just.....

Ok, as a PC user, this seems like an obvious thing to do, so maybe I'm missing somethign, but here goes.

If Apple (or any maker of any notebook), wants to improve performance of it's notebooks while not having to sacrifice significant battery life each time they add a faster CPU, why don't they simply eschew raw CPU mhz for from front-side bus speed?????

In my time on both Intel and AMD based systems, increasing the FSB has made an enormous difference in system performance. In fact, my mom's 1.8ghz athlon with a DDR FSB of 266mhz is not nearly as fast in tons of situations (games, photoshop, web browsing, overall system performance) as the chip is when I downclock it to 1.6ghz, but up the FSB to 400mhz or higher.That said, couldn't Apple make significantly more powerful notebooks if it simply upped the FSB of it's memory and chipset?? Honestly, a 1ghz CPU running at a FSB of 400 or 450 or 500mhz (or even higher) (which is more than doable with today's memory) would smoke the bejeezus out of, say, a 1.0-1.33 ghz CPU with a 266 or 333fsb. On top of that, keeping the chip at a lower speed would keep battery life long.

It seems to me that Apple should stop worrying a/b the raw ghz (don't get me wrong, however, more is certainly better) of it's notebooks and simply name their peformance levels A, B, C, D, etc, and then let the performance of the system be (along with the existing sex appeal), the main selling point.

I hope I didn't say something you all alreayd have said or sounded arrogant or antogonizing, just that I think apple generally makes wonderful products and could increase their reputation as innovators if they pursued this particular niche of notebook technology.

eburness said:

Ok, as a PC user, this seems like an obvious thing to do, so maybe I'm missing somethign, but here goes.

If Apple (or any maker of any notebook), wants to improve performance of it's notebooks while not having to sacrifice significant battery life each time they add a faster CPU, why don't they simply eschew raw CPU mhz for from front-side bus speed?????
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First of all, you're absolutely correct. The FSB speed of the G4 PowerBooks is abysmal; a 167MHz bus feeding a 1.5GHz chip (as on the top-end PB's) leaves them seriously data starved.

My understanding is, though, that the limitation is the G4, and not the system. Motorola produces the G4 for Apple (and other customers, mainly in the telecom/networking sector) and only their engineers can up the FSB speed. Motorola's inability to do this is what has lead Apple to use the IBM-made G5 in its newest desktops. (Note that the G5 may run at only 2.5GHz, but it's FSB runs at half the processor clock...an awe-inspiring 1.25GHz on the top-end model, and a very respectable 900MHz on the low-end 1.8GHz unit.)

If you look closely at the specs for the PowerBooks you notice something: The FSB runs at 167MHz, but the memory is twice that speed (333MHz effective clock DDR.) The memory is really quite fast, but the processor can't keep up! (Though the on-chip caching helps some.)

This used to be a problem with the Power Macs as well. See the
Barefeats tests for more on that.

The G5 has effectively solved this problem in the towers, and as it migrates down, it will disappear in the PBs as well.

Thanks for the explanation.

plus you mentioned that apple is always concered about the raw mhz speed...well i dont think your correct..in the PC world yes...everything is about the mhz but in apples world its not overly a large deal as you may notice our top speed is only 1.33ghz while dells are shipping a 2ghz. apple doesnt need to be concered about the speed cause our OS can properly handle the the CPU usage. infact im using the REV A albook and only have a 1ghz and its faster than many models of pc's ranging up to 2.2ghz...im sure you will notice that with new macs coming out that they are focusing on the FSB

It's a completely different architecture, that's the reason for the higher ghz on PC's, it's just measured differently, so I think they have a point.. it would be interesting to hear this conversation go further.. some good stuff going on!

PowerbookG417 said:

plus you mentioned that apple is always concered about the raw mhz speed...well i dont think your correct..in the PC world yes...everything is about the mhz but in apples world its not overly a large deal as you may notice our top speed is only 1.33ghz while dells are shipping a 2ghz. apple doesnt need to be concered about the speed cause our OS can properly handle the the CPU usage. infact im using the REV A albook and only have a 1ghz and its faster than many models of pc's ranging up to 2.2ghz...im sure you will notice that with new macs coming out that they are focusing on the FSB

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Sorry, let me rephrase that one, b/c you're right. What I meant to imply is that Apple's ability to lure in new customers from the Wintel and WinAMD market is somewhat hindered by the fact Macs cannot boast comperable CPU speeds in terms of RAW megahertz, which is a huge barometer of performance for lots of people who know little about computers (yes, I know AMD runs it's chips at a lower clock-speed also, but they have a numbering system that makes it easy to understand how their chips stack up against Intel's). I mean, most enthusiasts agree that AMD makes the fastest chip (Athlon 64 FX-53), but many people who just buy a computer fromt best buy or circuit city assume their Intel equipped system is the best money can buy.

****And to add to my earlier point about the front side bus, here's another reason why Apple should pursue that strategy that I can see. Whereas the latest Intel and AMD mobile chips automatically downclock themselves when using fewer system resources (ie: running fewer or less power hungry apps), the Apple mobile chips (so far as I know, feel free to tell me otherwise), do not. That said, wouldn't it make sense to be able to have, for instance, a 1.33ghz G4 be able to downclock itself to 600, 667, 800 mhz, etc when all ur doing is some mobile word processing. And wouldn't a higher front-side bus help offset any drop in performance in such situations (ie: have a CPU multiplier of 4, and a front side bus speed of 200mhz [400mhz effecrtive])?? Wouldn't that also increase the ibook or powerbook's battery life dramatically??

eburness said:

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Whereas the latest Intel and AMD mobile chips automatically downclock themselves when using fewer system resources (ie: running fewer or less power hungry apps), the Apple mobile chips (so far as I know, feel free to tell me otherwise), do not.
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Yes, they do. Where do you think Intel got the idea for SpeedStep(TM)

But again, most of these are limitations of the PowerPC G4, and there's not much Apple can do about that. Only a different processor (the G5, for example) can change things.

You are all forgetting something very important in the equation: __ cache __

Modern microprocessors have over 99% cache hit rate with their L1 and L2 cache. Do you know what that means? You'll notice the effect of slow FSB only when there is a cache miss, which is on average 1% of the all time. All the instructions are prefetched for the CPU, and most of data is available when the CPU needs them. The CPU never sits idle waiting for data if it's already in the cache.

The effect of fast FSB is small. It's not like CPU where 1GHz G4 is roughly twice as fast as 500MHz G4. FSB speed is important, but it's not going to boost the speed of your computer as you claim. If you did see large performance improvement with faster FSB, you probably misconfigured the cache setting.

In other words, 500MHz FSB is not going to be 5x faster than 100MHz FSB when running average applications. It's not even going to be twice as fast. The speed increase will be just barely noticeable.

There is an exception, and there are applications that demand A LOT of data constant data transfer which will basically invalidate the cache all the time and cause the data load from main memory. Maybe some 3D game with a lot of textures that need to be loaded frequently. Maybe doing a large matrix calculation. But not word processors or web browsers that people use most of times.