# iMac G5 / PowerMac G5 performance



## HateEternal (Sep 1, 2004)

Has anyone seen any benchmarks between the PowerMac G5 and the iMac?

The iMac G5 is a killer price for a G5 and an apple flat screen. I wanna know what kind of performance you are losing.

I might actually think about getting a iMac for that kind of price.


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## Ricky (Sep 1, 2004)

The system bus is slower than it should be to allow maximum performance, which would take things down a notch.


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## fryke (Sep 1, 2004)

You could maybe say that an 1.6 GHz PowerMac G5 would more or less equal an 1.8 GHz iMac G5 in performance. But that's not a choice you have right now. Basically, the PowerMacs are all dual processor machines, while the iMac's just got one of them. Plus, as mentioned, the bus speed and probably also a bit of graphics card difference. Depending on what one does, the machine will be more than enough, but for other uses, there just isn't an "enough". ;-)

Also: The killer price is killed two years later, when you want to upgrade to a G6 (or G5plus or whatever), because with the iMac you'll have to buy the screen _again_, whereas the separate Cinema Display will still be a good display for another new PowerMac...


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## Ricky (Sep 1, 2004)

fryke said:
			
		

> but for other uses, there just isn't an "enough". ;-)


 Well said!  I can't tell you how much of my time is spent waiting for Photoshop to finish tasks I give it.


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## ElDiabloConCaca (Sep 1, 2004)

I would assume that a maxed out iMac G5 wouldn't be nearly as fast as a low-end, stripped down PowerMac G5.  They're in different categories: one in consumer, one in pro.  It's really tough to compare two computers that differ across categories, since the hardware is radically different (bus speed, number of processors, etc.).  Typically, anything in the pro category will be faster than anything in the consumer category, unless you get REAL extreme and compare low-end pro to high-end consumer -- then the line gets slightly blurred.

A more feasible comparison would be an iMac to an iBook, or a PowerMac to a PowerBook.


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## HateEternal (Sep 3, 2004)

I realize the hardware differences... I was wondering if any one had seen ACTUAL stats on performance differences.


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## fryke (Sep 3, 2004)

You _really_ think, ElDiablo, that a 1.2 GHz iBook G4 is 'nearer' to an 1.6 or 1.8 GHz iMac G5 than an old single processor PowerMac 1.6 or 1.8 GHz? The 'pro' and 'consumer' tags alone do _not_ make such a difference. If you have, say, an 'old' PowerBook G4 867 MHz (a Titanium), then a new iBook G4/1.2 GHz will beat it. Probably in _every_ test.

The question is, in my humble opinion, an interesting one, because now that the iMac's got a G5 processor, many professionals might consider the iMac a good alternative for some jobs...

I, for one, am quite interested in the benchmarks that will compare

- iMac G4 1.25 GHz
- PowerMac Dual G4 1.42 GHz
- iMac G5 1.8 GHz
- PowerMac G5 Dual 2.5 GHz
- PowerMac G5 Single 1.8 GHz

etc.

Where will the new iMac end up? Above the ex-pro G4/1.42 GHz machines? Would it even match (older) single processor G5 PowerMacs? We don't know yet. We can just make assumptions on how the bus speed, graphics card and harddrives will impact the benchmarks of the iMac G5, because the bus speed for all _other_ G5 machines has always been 1/2 processor speed...


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## ElDiabloConCaca (Sep 3, 2004)

fryke said:
			
		

> You _really_ think, ElDiablo, that a 1.2 GHz iBook G4 is 'nearer' to an 1.6 or 1.8 GHz iMac G5 than an old single processor PowerMac 1.6 or 1.8 GHz? The 'pro' and 'consumer' tags alone do _not_ make such a difference. If you have, say, an 'old' PowerBook G4 867 MHz (a Titanium), then a new iBook G4/1.2 GHz will beat it. Probably in _every_ test.



Oh, most definitely true, but it's absurd to compare a 3 year old pro machine to a currently-shipping consumer machine.  Of course the comparison between pro and consumer must be done with models of the same era.

Pro and consumer alone don't make much difference, but I'm not backing off of my claim that typically, the pro machines will spank the consumer machines.  You can't rely completely on "pro" and "consumer," but you can rest assured that the pro machines will cost more and be faster.

The iMac G5 looks promising, but is hobbled in comparison to the pro machines in terms of bus speed and graphics power.  

I'd like to see some numbers on the new iMac G5 as well, but I don't think they'll be as great as we all want them to be.


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## fryke (Sep 3, 2004)

The comparison between pro and consumer _does NOT have to be done_ with models of the same era. Because people first have to compare their _old_ hardware with current offerings. And the iMac G5 might appeal to professional users of older G4/G5 PowerMac hardware... That's why I think the question is still legit.


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## Ricky (Sep 3, 2004)

HateEternal said:
			
		

> I realize the hardware differences... I was wondering if any one had seen ACTUAL stats on performance differences.


 I'd like to see that too. It'd be quite a sight to see an machine which is not shipping yet showing up on a benchmarking site. 

    Bring on the 10 THz G6 optical processor benchmarks while you're at it!


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## Go3iverson (Sep 3, 2004)

This is the very same question I'm pondering myself and if anyone wants to lend some buying advice, I'll take it under consideration!

I'm currently trying to decide on a new study machine.  This machine will be used primarily for Server and for studying for the ACSA, but probably not for daily usage or important work.  My plan is to buy the next generation tower (hopefully 3GHz) with a large (23" or 30") when the display prices come down, the machines hit that magical 3GHz mark, and I hopefully have received a promotion to better afford all of that!  This machine will run all my personal apps and have my personal data, to keep it safe from my work machine and data.  I'd love to have my Final Cut Pro on there and hope to add Shake and Logic.

Now, for those apps, the obvious choice is the PowerMac, but my current need is for testing.  I was pretty content with my 533MHz G4 tower, that I sold, but pricing between a refurb G5 and iMac G5 are pretty close, which makes it even harder to decide.

Its funny, to get back to performance and prove the point of the upgrade debate and comparing different generations.  While I've owned iMacs and I like them, we all get so enthused by the duals and the PowerMacs that we lose sight in the fact that going from 533MHz PowerMac G4 with 133MHz bus to a 1.8GHz G5 iMac with 600MHz is just a ghastly gain in performance, let alone the fact that, in my case, I'd move from an Envision 15" LCD connected via RGB cable to an Apple branded, integrated, 20" display, with no extra cables or mess.


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## HateEternal (Sep 3, 2004)

Ricky said:
			
		

> I'd like to see that too. It'd be quite a sight to see an machine which is not shipping yet showing up on a benchmarking site.
> 
> Bring on the 10 THz G6 optical processor benchmarks while you're at it!



Graphics card benchmarks always come out waaaaaaaaay before the shipping date. I was just hoping someone knew of a place that got the same kind of in that sites like HardOCP and anandtech get in the PC world.

I really want to know if that 700 dollar price difference is worth it or not.

I know the iMac is the consumer machine and the PowerMac is pro, but i still want to see how they stack up.

Wouldnt you want to know if it was worth it to pay the extra 100 bucks on a non pro graphics card versus the pro? I know I do.


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## Go3iverson (Sep 3, 2004)

I guess we could go about it the long way...

Does anyone know where there are good benchmarks showing the overall system performance of the previous generation iMac G4's?  Since Apple used those machines as their baseline for the iMac G5 performance evaluations, that would be a way to get an idea of where this new machine fits.


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## Go3iverson (Sep 3, 2004)

Ok, so, to start answering my own question.... 

http://reviews.zdnet.co.uk/hardware/desktops/0,39023846,39118219,00.htm

That is a comparison between iMac 1GHz/256MB, iMac 1.25GHz/256MB, and PowerMac Dual 2.0GHz G5/2GB (can we get these numbers much further apart!?).

(I'm no math guy, so if I'm off, sorry!  You get what you pay for!)

In iMovie, the Dual 2 was about 39% faster than the 1.25GHz
In iTunes, the Dual 2 was about 225% faster than the 1.25GHz (WOW)
In Quake, the Dual 2 performed about 391% better in the frame rates than the 1.25GHz (ultra wow!)

**Note, they don't say what video card was used in the benchmarks for the dual 2.0GHz, but it does state that the NVIDIA GeForce FX 5200 Ultra 64MB was used in the iMac 1.25, which is the same in the iMac G5, I believe**

Now, according to Apple's site, compared to the 1.25GHz iMac G4, the G5 is 189% faster in HALO, and 212% faster in Unreal Tournament 2004.  If we want to apply those numbers to Quake's performance numbers on for the 1.25GHz iMac, which I know is not accurate as code is different and such, we could guess that, shockingly enough, that the iMac would put up roughly half, probably a little under half, the performance of the PowerMac, which makes sense being that it has 1 CPU instead of 2, a 600MHz bus instead of a 1GHz, and half the video memory.  We should note that the Apple test machine was using 1GB of RAM and not the 256MB that zdnet did.

The Apple benches also state 46% increase in iMovie/Keynote, which might actually bring iMovie performance up to the PowerMac's numbers (in theory, according to what we can see here and not by using logic that two CPU's are stronger than one), a 71% increase in GarageBand, 56% increase in Photoshop and a 67% increase in FCE rendering.


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## Go3iverson (Sep 6, 2004)

The iMac thread provided us with a benchmark of the iMac G5, stating a 155.53 overall system performance.

For those of us with PowerBooks out there, I just ran Xbench on my two-month-old 1.25GHz PowerBook G4 with 1GB of RAM and 64MB video, so configurations should be "close".

The overall score of my PowerBook is 88.39, much lower than the iMac G5.  CPU was just killer.  My score was 87.85 compared to 170.42.  Yes, we don't "work" in benchmarks all day long, but for the original poster, this should begin to give you an idea of the performance of the iMac.  

Xbench.com has lots of benchmarks available to compare.  If you'd like, I could also submit mine as well.  We have some 1.25GHz Dual's at work, so on Tuesday, if everyone would like, I can run this utility on one of them, if you would like to be able to "ask the author" any in-depth configuration questions and not just see numbers.  What other machines do we have represented here?  I have access to a wide variety.  I'd be interested to see teh score of the dual 1.8GHz machines we have.  Yes, I know I could just read the site, but I like being able to actually compare the numbers to how the machine feels when I can use it...and I can't use all those other 1.8's listed on the site daily, if I please!


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## Viro (Sep 6, 2004)

No offense, but your Xbench scores are way off. You need to make sure that your CPU is running at Highest performance. The scores you're reporting tell me that for your powerbook, you have either set the performance to 'Automatic' or 'Reduced'. Run it again with performance set to 'Highest'. On my PB 1.33 Ghz with those settings, I get a score of 160.67. Given that the iMac has a 500 Mhz advantage, this doesn't bode well for the G5 line of processors.

The overall score of my system is 122, which is about 30% less than the iMac. This is quite surprising, as notebooks tend to offer much slower performance than desktops. This can be attributed to different factors, namely
a) hard disk speed. Most laptops come with 4200 RPM drives. Most desktops come with 7200 RPM drives. This is nearly twice as fast in certain operations compared to notebook drives.
b) processors with more cache. Nuff said.
c) Different motherboard chipsets. Don't know if this is true in the Apple world, but in the PC world, laptop motherboard chipsets can't compare with desktop motherboards when it comes to memory bandwidth. The iMac G5 has a FSB of 600 Mhz (IIRC), while the Powerbook has a measly 166 MHz bus. The iMac should be mopping the floor with the Powerbook.

All in all, if that is the performance of the iMac, I'm not impressed.


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## Go3iverson (Sep 6, 2004)

System performance was at highest, believe it or not.  But, now that I think about it, I haven't restarted this system in, well, I don't remember when!  Probably a few weeks ago when I installed 10.3.5.  I'm going to reboot it and run again in a few.  They seemed low to me too!


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## Go3iverson (Sep 6, 2004)

Reboots rock!  I double checked everything and ran a few utilities before running Xbench on a clean reboot and received an overall score of 115.27.  Ran it again while typing this and received 115.98.

You said that your laptop, a 1.33GHz PBG4 scored 122, so I guess that makes sense, considering mine is a 1.25GHz.


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## Viro (Sep 6, 2004)

Yeah, rebooting is a good habit. Sure, you don't need to, but doing it does help system performance.

So you can see, for a machine that boasts a 500 - 600 Mhz clock speed advantage coupled with a 333 Mhz FSB advantage, the performance of the G5 iMac isn't really much to write home about. That's my opinion and YMMV of course.


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## HateEternal (Sep 6, 2004)

Although I would still like to see how performance is different, I think that I have decided that the Dual 1.8 is a way better deal, superdrive more upgradability, Radeon 9600XT for 50 bucks. Better deal in my opinion.

One question though, on apples store they say the 1.8 has 3 PCI slots, not PCI-X, but there is an option to add a 1GB PCI-X card in the customize page. Which is the mistake? Does it have PCI-X or does that card not go in there?

thanks to anyone who spent time looking for stuff.


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## Go3iverson (Sep 6, 2004)

I'm pretty sure the motherboards used in the low end models do not use PCI-X, they also only support a mere 4GB of RAM instead of 8GB (though some claim that the board should support a full 16GB of RAM using the 2GB modules, its just amazingly expensive to configure that!).

See, for my purposes I'm thinking of the exact opposite.  I can take the internal 160GB drive in the iMac G5 and make 4x40 GB partitions, running 10.3 Client, 10.3 Server, 10.4 Client, 10.4 Server and be able to use whatever I need, wherever I need it ASAP.  I'm thinking this machine would be a great server for me, especially considering the machine I used before rated about 70-80 on xbench.com, so 155 is a huge upgrade in that sense...

I'm still holding my developer discount for the next PowerMac revision, so I can get a full graphics workstation...I just hope its not all the way at WWDC again.  I think it'd be a mistake to make only yearly industrial grades updates.


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## HateEternal (Sep 7, 2004)

After looking through the hardware page i am sure that the dual 1.8 PM does not have PCI-X. I was just wondering because of that customize page had the PCI-X NIC as an option.


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## stingerman (Sep 8, 2004)

When comparing the new iMac G5 to the PowerMac G5 1.6, keep in mind that the PowerMac was using DDR333 single channel compared with the iMac's DDR 400 single channel, with the latter's FSB more than adequate to handle the throughput.  Considering the "U3 lite" does not need to handle cache coherency and there is no need for dual pipeline switching, the iMac's memory latency should also be faster.  Again, this is in comparison to the single processor PowerMac G5.


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## Go3iverson (Sep 23, 2004)

Ok, I ran XBench on a new (original) Dual 1.8GHz G5 with 250GB drive and 1GB of RAM.  Video is standard NVIDIA.  Got a 211.43 score.  So, that's pretty much double what my 1.25GHz PowerBook scored.  I'll bench my iMac when it arrives, sometime!


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## hulkaros (Sep 24, 2004)

iMac G5 vs the rest of the "family":
http://www.barefeats.com/imacg5.html

Nice?


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## Viro (Sep 24, 2004)

The performance doesn't look too bad, actually. I would have liked it more if they had compared the 12" Powerbook as well since that is quite close in price to the iMac.


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## fryke (Sep 24, 2004)

Looking at the PB's scores, I guess a PB G5 wouldn't currently even do us that much good, AND kill our battery lives... Kinda glad there'll be another G4 PowerBook. These G5 processors just don't seem 'ready' yet - unless you also have the surrounding technology to back it up. That's quite clearly what sets the 2.0MP in those tests apart - and we all know that the space restrictions of a PowerBook do not allow for, say, graphics cards with their own fans that are three times as thick as a PowerBook.


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## Go3iverson (Sep 24, 2004)

Fryke -

Yes and no.  Motion, as I understand it, and please correct me if I'm wrong, is built to be very intensive on graphics card performance.  We see the cream of the crop of cards rising to the top in these tests easily.  After that, in gaming, we see that the iMac G5 and the PowerBook G4 are about the same.  

When we get to Cinebench, which always makes me want to go to the mall to Cinabun or whatever its called, we see about a large (90-ish%) increase in performance from iMac G5 1.8 to 1.5 PBG4.  We see iMovie score about 20% faster and so on.  

I'd be also interested in seeing a PBG4 benchmark with the 128MB card installed, since a PBG5 would probably have a quick upgrade available to 128MB as it does now.  Also, it'd be interesting to see a PowerMac G5 1.6GHz outfitted with 128MB of ram perform, as that would be close to a 1.6-1.8GHz iMac G5, but with the ability to see how video performance works with the G5 architecture even further.


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## Viro (Sep 24, 2004)

The gaming benchmarks actually seem to favour the Powerbooks. This is because the Powerbooks are equiped with the Radeon 9600, which is a much better video card compared to the iMac G5's Geforce fx5200 Ultra.

Looking at the rest of the performance benchmarks, it seems that the iMac has about 20% better performance(iMovie and Filemaker) compared to the 1.5 GHz Powerbook. This can be put down to the clock speed advantage since the 1.8GHz iMac is clocked 20% more than the powerbook. The iMac handily beats the Powerbooks at Cinebench largely because of it's much stronger FPU. This is speculation on my part, btw.

It performs very poorly in Motion, even when rendering is off. That's really dismal performance.

After examining the results more closely, I have to retract my previous statement. The performance of the G5 iMacs are quite lack luster in my eyes. A Powerbook G5 is hopefully a long way off.


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## Go3iverson (Sep 24, 2004)

I agree and disagree.  With Tiger, the code is being even more geared towards the strengths of the G5.  If we're looking at Tiger shipping by mid 2005 and the PowerBook G5 at WWDC, for arguments sake, we should see those numbers change greatly.  I'd expect the iMac G5's performance to be increased as well, if Apple gears Core Video towards G5 and has Motion take advantage of it, which I'm sure they would.

To say that the performance of the G5 iMac is lackluster may be slightly shortsighted, no offense please.  We all expect G5 to be faster and more capable and in some tests, it was, but we also have to consider that a 1.8GHz iMac G5 is about $1500 compared to a $2500 laptop.  Its good to see that the portable line is still packing a punch, but I would think that Tiger, especially with Apple's Pro-Apps will show improvements.  I haven't used Tiger on G5 architecture yet, but that's not a really fair evaluation either being that Tiger is still very far from complete.  On the other hand, on my Athlon64 system, moving from XP Pro to XP Pro 64 Beta showed large speed increases in the OS.  It wasn't a slow machine to start with, but you could see a difference.

I think a lot of what we're seeing is the graphics card, which is why I'd be interested in seeing a 1.6GHz PowerMac with 128MB graphics installed.  If they were to have a 1.8GHz PowerBook G5 today with 128MB pro graphics card installed, we may look at this differently.


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## mindbend (Sep 24, 2004)

http://www.macworld.com/2004/09/features/imacbenchmarks/index.php


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## ElDiabloConCaca (Sep 24, 2004)

Don't think these tests have been posted here yet, so here they are:
http://www.ppcnux.de/modules.php?name=News&file=article&sid=4092

I remember someone here pondering the performance difference when the iMac G5 uses matched RAM sticks vs. unmatched RAM sticks.  Ponder no longer.  The performance increase is significant.


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## HateEternal (Sep 24, 2004)

hulkaros said:
			
		

> iMac G5 vs the rest of the "family":
> http://www.barefeats.com/imacg5.html
> 
> Nice?



I don't get it. Dual G4 1.42 stomps all but the 2.0Ghz G5. Is the 2.0 much better than the 1.8, other than the PCI-X and the extra memory slots what is different?

Edit: Never mind, the ones the the 1.8 G5 does bad in I am assuming  are dependant on video card. Which is why I am planning on getting a 9600XT in my G5. 50 bucks is so worth it.


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## Viro (Sep 26, 2004)

Go3iverson said:
			
		

> I haven't used Tiger on G5 architecture yet, but that's not a really fair evaluation either being that Tiger is still very far from complete.  On the other hand, on my Athlon64 system, moving from XP Pro to XP Pro 64 Beta showed large speed increases in the OS.  It wasn't a slow machine to start with, but you could see a difference.



That's a very different move . The x86 architecture has always been hampered by a design that dates back to the 70s. One of the biggest drawbacks of that design is the lack of registers[1]. Think of registers as a high speed memory on the CPU for it to store data that it is currently working on. Data and instructions get fetched from RAM and is placed in registers for the CPU to work on[2].

The x86 has 8 general purpose registers (GPR). While this was sufficient in the 70s, it isn't sufficient today. This has been one of the criticisms of x86 and is addressed to a certain extent by x86-64(or AMD64 or EMT64 which is basically the same thing). The x86-64 spec extends the number of GPRs to 16, basically doubling it. It is estimated that a simple recompilation of standard x86 code to x86-64 code results in an approximate 20 - 30% speed improvement[3]. Due to the increase in GPRs which is expected on register starved processor architectures. The move to 64 bits has little to no impact on the performance of a processor. In some cases, you actually see a drop in performance[4].

This is not the case with the PPC architecture. Right from the very start, the PowerPC architecture was designed with *32* GPRs. The main advantage of moving to PPC64 is the increased amount of addressable RAM which is a good thing if you're working with very large documents like video files, etc.

It's a sunday afternoon where I'm at, and I'm a little too lazy to dig up references to what I've said. A quick search google on the terms that I've posted should turn up the references needed 

references:
[1] The AMD64 ISA value proposition, page 9 http://www.amd.com/us-en/assets/content_type/DownloadableAssets/dwamd_Value_of_AMD64_White_Paper.pdf
[2]FOLDOC, http://wombat.doc.ic.ac.uk/foldoc/foldoc.cgi?query=register&action=Search
[3]Anandtech, Linux desktop CPU rounduphttp://www.anandtech.com/linux/showdoc.aspx?i=2213&p=2
[4]OSNews, Are 64bit binaries slower than 32 bit binaries, http://www.osnews.com/story.php?news_id=5768&page=2


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## Go3iverson (Sep 26, 2004)

Viro,

Now *that's* a reply!  I knew drips and drabs of that info, but that was a very well thought out, comprehensive comparison and is greatly appreciated!  Especially conisdering its a Sunday!  

I have heard questions of if 64 is slower than 32 and I've heard some compelling arguments.  My argument back to them was, for my case, being an argument over the huge increase Apple users gained in the G5, was "I don't care if its technically slower or not, in the realm of OS X, plunk down in front of a dual 1.42GHz G4 and a dual 2.0GHz (high end at the time) G5 and tell me you don't feel a performance gain!"  

Scientific, no, but true!  But I do understand the arguments on either end, for the actual 64-bit part of this argument, not the ghastly leap forward to having dedicated buses that run at 1GHz instead of a shared bus of 167MHz and such.


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## ElDiabloConCaca (Sep 26, 2004)

I think preliminary tests of 64-bit speed vs. 32-bit speed would be incomplete (or possibly inaccurate), since we really don't have a true 64-bit OS to test it with.

I do agree with Viro that the more GPRs you have, the bigger speed increase you'll see.  As an Assembly programmer, where you work directly with the registers available, I can say from experience that having more registers to work with produces shorter and more compact (and therefore, faster-running) code.  The number of GPRs available on the processor is probably the main influence behind the old "PPC is faster than x86 at the same clock speed" debate.


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## Viro (Sep 26, 2004)

The G5 produces much better performance than the G4 on certain applications because it has a much more powerful FPU. Just look at some of the XBench CPU scores and you'll see that the floating-point performance is spectacular. I even venture to say that the FPU of the G5 is better than that found on the Athlon, which is no small compliment! Other enhancements to the G5 include like you've said, a much faster system bus.

However, all these things are there even today in the absence of a true 64 bit operating system and users already reap the benefits. So the question is will moving to 64 bits improve anything? Unless you need to address more memory, the answer is a resounding no.

Briefly, a lot of this has to do with fetching data from RAM. Moving from 32 bits to 64 bits effectively doubles the cache lines. This is a bad thing. Data in the CPU cache is stored in lines of a fixed size. For example, if your CPU had a cache line of 64 bytes, if you needed just 1 byte from RAM, 64 bytes would be read. Going to 64 bits on this theoretical CPU would _*normally*_ mean that the cache lines double in size. So if you needed 1 bytes from RAM, you'd end up reading 128 bytes from RAM. You can imagine that your cache is now less efficiently utilized.

On a side note, this effect of can be reduced by some clever programming, sometimes called locatlity optimization. This basically ensures that the data that is normally operated on together is stored close together in RAM so that when data is fetched from RAM to cache, the chance of wasting cache becomes less. Even with _perfect_ locality optimization, all that happens is that the effect of doubling the cache lines gets negated, and you're pretty much back to square one (i.e. 32 bit processor).

A 64 bit processor isn't strictly going to improve performance. It is however a nice marketing number . This is not to say that Tiger won't sport any performance enhancements. Look at the move from Jaguar to Panther. I _noticed_ the performance gain. Same for the Puma to Jaguar move. The only question that remains, is how much of the performance gain in Tiger was due to the move to 64 bits? The answer is most probably none.


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## Viro (Sep 26, 2004)

@Eldiabloconcaca

PPC is faster than x86 at the same clockspeed. It just depends on what apps you run


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## ElDiabloConCaca (Sep 26, 2004)

Yep, and that's something I've thoroughly "preached" to those that will listen... 

...but the question is, "Why?"  Is it CISC vs. RISC or some variant thereof?  Is it because we have more registers to work with, and, if so, is that still true of the G5 and the AMD/Intel processors?


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## Lycander (Sep 26, 2004)

Go3iverson said:
			
		

> "I don't care if its technically slower or not, in the realm of OS X, plunk down in front of a dual 1.42GHz G4 and a dual 2.0GHz (high end at the time) G5 and tell me you don't feel a performance gain!"
> 
> Scientific, no, but true!


Actually it's very much scientific. Those 2 machines you mention are both running in 32 bit mode. The G5 system is ~600MHz faster (per CPU) than the G4 system, and has a faster system bus. So it's a no brainer that the G5 is better in your comparison, you could have just stopped at "it has more MHz" and call it a day.



			
				ElDiabloConCaca said:
			
		

> ...but the question is, "Why?" Is it CISC vs. RISC or some variant thereof? Is it because we have more registers to work with, and, if so, is that still true of the G5 and the AMD/Intel processors?


Having more registers is one thing, but being able to move data quickly is another. Modern AMD/Intel CPUs compensate for lack of registers by having very fast memory buses. The G5 comes along and gives us best of both worlds.

As great as the PPC FPU is, their ALU is very lousy. If you do any MacOS programming, especially in OSX with Cocoa, why do you think Apple chose to use floating-point data types in their API even for whole numbers?


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## Viro (Sep 27, 2004)

ElDiabloConCaca said:
			
		

> Yep, and that's something I've thoroughly "preached" to those that will listen...
> 
> ...but the question is, "Why?"  Is it CISC vs. RISC or some variant thereof?  Is it because we have more registers to work with, and, if so, is that still true of the G5 and the AMD/Intel processors?



A lot of it has to do with the pipeline length of the processor. RISC CPUs tend to have very short instruction pipelines while CISC CPUs tend to have longer pipelines. Incidently, Arstechnica recently had a series of articles on pipelining and they can explain this a lot better than I can, in simple terms for the lay person. Which I think is great! http://arstechnica.com/paedia/p/pipelining-1/pipelining-1-1.html

Somewhere on that site is also quite possibly one of the best expositions of the G5 architecture. I really recommend reading the articles on that site, to get a general knowledge of the current crop of CPUs be it from Intel, AMD or IBM. They cover and explain them really well. If you're keen on knowing more about CPUs in general, Computer Organization and Design by Patterson and Hennessey is a book I swear by. Even I understood it


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## Go3iverson (Sep 27, 2004)

Lycander said:
			
		

> Actually it's very much scientific. Those 2 machines you mention are both running in 32 bit mode. The G5 system is ~600MHz faster (per CPU) than the G4 system, and has a faster system bus. So it's a no brainer that the G5 is better in your comparison, you could have just stopped at "it has more MHz" and call it a day.



Oh, I know.  The person who was talking with me was not familiar with the G5, oddly enough.  It was months after the launch and they work in IT as well.  It was more of a comparison of high end x86 architecture to high end Apple branded PPC architecture, for desktops.  

His comment was that 64-bit could actually slow down the machine, as if the application is simply sending 32-bit chunks of data, that the CPU simply processes an extra 32-bits of blank info.  My response back was, that I didn't care if it did, or didn't do that, being that the bus, etc was such a huge step forward. 

Remember, to people who are unaware of the new breed of Apple offerings, most will still assume 100-133MHz FSB and, if they knew beyond that, shared bus between the cpu's as well.  So explaining that 2GHz wasn't smoke and mirrors, is more than just saying "its faster".


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## Lycander (Sep 27, 2004)

Viro said:
			
		

> A lot of it has to do with the pipeline length of the processor. RISC CPUs tend to have very short instruction pipelines while CISC CPUs tend to have longer pipelines.


CISC vs RISC has nothing to do with pipeline lengths. Intel (and to some extent AMD) choose to use longer pipelines in order to scale their chips higher in MHz, that's all a marketing ploy, bad Intel!

The whole "shorter" pipeline argument is getting kinda old and irrelevent now a days.

http://www.cpuplanet.com/features/article.php/2233261

_but where the G5 really pummels its predecessor is in pipeline length: Instead of the original G4's 4-stage or G4+ chip's 7-stage integer pipeline, the PowerPC 970 follows the superpipelined approach of the 20-stage Pentium 4 with a 16-stage integer pipeline -- 21 stages for floating-point instructions, as many as 25 stages for single-instruction-multiple-data (SIMD) multimedia instructions._

So there's more than one pipeline to be concerned with, but we typically hear chip companies touting the smallest number. Back when Apple was showing that presentation about pipeline length, that shorter is better, it only showed one side of the story. The whole idea behind pipelining is to constantly feed instructions and data to the CPU. The presentation illustrated this with little circles (or something) marching through a "pipeline" and when the nasty ol' branching instruction came along it forced the pipeline to flush and everything has to be reloaded. 

Yes that does sound like a performance bottleneck. But what the presentation neglects to show is that the x86 rivals often had double the bus speeds of the G4. So what if they had to flush a 20 stage pipeline. The bus speeds were running almost 4 times faster than the G4's that it could flush and refill the pipeline and the penalty is not as bad as Apple makes it out to sound.

With the G5 we start seeing real improvements in bus speeds and how fast it can move data. The PPC architecture is a great number crunch, no doubt. But it was starving for data on a 133 MHz bus. Putting DDR RAM in a G4 system is completely USELESS because the G4 CPU and chipset was not designed for DDR. Going from a pipeline length of <10 stages (G4) to double digits (G5) didn't wreck performance did it? But the result? Higher clock speeds, 2+ GHz. And with the faster FSB and overall system bus, it can flush and refill the pipeline without a hitch. But that's what CPU cache is for, that's what prefetching is for. I'm more concerned with the branch mis-predict features more so than pipeline depth. AMD chips as well as IBM chips have very good branch mis-prediction handling, so they don't suffer too much when branching code causes the CPU to mis-predict the next instruction location. Intel's CPUs are notoriously crappy at branch mis-prediction, that's why everyone else could stomp a P4 in certain tests.


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## HateEternal (Sep 27, 2004)

I certainly don't have as good of an understanding of cpu function as you guys do, but if running 64 bit code is slower than running 32 bit, how come 32 bit is faster than 16? Why wern't these problems encountered when going from 16 to 32? Does the technology just need to be perfected?


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## Viro (Sep 27, 2004)

HateEternal said:
			
		

> I certainly don't have as good of an understanding of cpu function as you guys do, but if running 64 bit code is slower than running 32 bit, how come 32 bit is faster than 16? Why wern't these problems encountered when going from 16 to 32? Does the technology just need to be perfected?



The overhead incurred by going to 32 bits greatly offset the disadvantages of 16 bit processors. Back in the days of 16 bit processors and OSes, a lot of hacking was done in order to get the CPU to recognize more than 64K of RAM (2^16 = 65536). Most OSes got around this by using a segmented memory model, where the RAM in a computer was divided into segments of 64 KB each. 

This effectively meant that the computer could only effectively work with 64 KB of RAM at a time. You could access more, but you would have to do it in chunks of 64 KB of data. Working with data that didn't fit into these 64 KB chunks was a real pain and real slow. 

The move to 32 bits allowed up to 4 GB of RAM to be addressed. This also brought the move to a flat memory model, which basically meant no more dealing with segments and 64 KB chunks of RAM. All of the physical memory can be addressed and this brought a major speed increase.

At present, the move to 64 bits doesn't bring such a stark difference because we are no where near reaching the 4 GB limit, especially on home computers. However 32 bit servers with more than 4 GB RAM(think Xeon with PAE) and these use the dreaded segmented memory model of old 16 bit computers. Only difference is instead of 64 KB chunks, we get 4 GB chunks (or more commonly 2 GB, depending on implementation). These servers will see a considerable benefit from moving to 64 bits because they can get rid of this horrible segmented memory model.


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## soulseek (Sep 28, 2004)

HAIL THE KING !!! 

http://www.barefeats.com/pentium4.html



(its a shame they didnt use 4GB RAM instead of 2Gb... and maybe Tiger)


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## soulseek (Sep 28, 2004)

another interesesting article can be found here: http://osopinion.com/modules.php?op...=article&sid=2350&mode=thread&order=0&thold=0


this one concerning the G5


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## hulkaros (Sep 28, 2004)

And here is another "interesting" one:
http://www.popularmechanics.com/technology/computers/2004/4/desktop_brawl/print.phtml

A piece from there:
"Not being able to run SPEC tests, we turned to BLAST and HMMer, which are DNA and genome-sequence matching tests, as well as to Bibble, a batch image-processing application. The problem is that these tests do not run on Windows XP. In frustration, after running the SPEC tests on the HP xw6000 workstation, we installed Linux on the HP, which allowed us to run the new tests. And we were surprised. The G5 was 59.5 percent faster than the HP at processing 85 high-resolution color photographs totaling 684.6MB of data. In the HMMer tests (61.3MB of data), Apple was 67 percent faster than the PC and under BLAST (32.8MB), Apple was 85.9 percent faster. These results are in line with those now published on Apple's Web site."

Some VERY serious and heavy apps that show how easily a G5 can kill any P4/XEON based computers...

Then again those same P4/XEON can easily kill the G5 in Doom3!  Oh, I forgot... Doom3 isn't even out for the Mac


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