Analysis: x86 Vs PPC

Gentu writes "Nicholas Blachford (engineer of the PPC-based PEGASOS Platform) wrote a long and detailed article, comparing the PPC and the x86 architectures on a number of levels: performance, Vector processing and Power Consumption differences, architectural differences, RISC Vs CISC and more. The article is up-to-date and so it takes the G5 into account too."

Comments

UNIX was way before the X86:

[AtariAmarok]

You said "UNIX technology was created for the x86 architecture"

First x86: "The 8086 blasted away at amazing speeds of 4.77 and eventually 8 MHz -- hardly a calculator by today's standards. All this started in 1978."

(check here)

UNIX invented: "An
interactive time-sharing operating system invented in 1969
by Ken Thompson after Bell Labs left the Multics"

(click here)

These arguments are so tired

[uradu]

This isn't the '80s anymore where performance is the most critical issue and we jump platforms every time a faster architecture comes out, since we don't have a large software base anyway. Nowaways software IS the more important aspect, and only relatively few well-heeled, game-addicted geeks are going to jump on the PPC just because it's a fews ticks faster this week, and Jobs winked at them with that very special smile. Given the way this industry goes, IBM/Motorola will sit back again, wipe the sweat off their foreheads and take a breather, and before you know it, Intel/AMD will have a faster processor again.

If you have x-platform software that will compile painlessly on either architecture, go for it, switch with each faster chip. But for most others, I doubt performance rants like these will make much of a difference. After all, how many Mac users switch to the PC just for the performance during those stretches when the PC has the upper hand?

Re:These arguments are so tired

[Hard_Code]

Did you even read the article? It is not about how PPC is faster than x86. It's about how PPC is more *efficient* than x86 which leads in the long term to lower power usage, whereas x86 gets diminishing returns on ramping up their clockspeed and playing games shuffling registers, etc. He specifically mentions that CPU speed is not really as critical as the companies make it out to seem because there are diminishing returns due to other system components. He mentions that x86 is up against a thermal wall by 2004 although I don't know where he got that data (it may be in a footnote but I not going to go back just to check). Speaking as a gamer who runs a pretty loud machine that overheats in summer, I am VERY interested in chips becoming cooler, moreso than them getting faster (the hard work is typically shoved off onto a graphics card).

Re:PPC comes out on top!

[Alrescha]

"UNIX technology was created for the x86 architecture"

In other news, it has been discovered that the current crop of teenagers has invented sex.

A.

Truly suprising colnclusion, OR NOT!

[pbox]

Nicholas Blachford (engineer of the PPC-based PEGASOS Platform) says that the PPC is better than x86.

What an unbiased opinion. Maybe we should really hear the other side too. I like the article for the wealth of info, and we all know the shortcomings of the x86 platform, but the conclusion seems to be biased.

Or is it just me?

Re:Truly suprising colnclusion, OR NOT!

[stevew]

Yep, and he is still stuck back in the 80's with his RISC vs CISC arguments. He says that internally they pretty much look the same (which they do) but they're some how different because RISC is easier to make happen.

Well - today's RISC's aren't very RISCy anymore. ;-) Todays CISC's have the same aspect. The machines have all migrated to simpler cores running VERY fast, but then tagging on features like predictive branching, out-of-order execution, etc.

An example of where the guy goes wrong is in his discussion of the compilers. What he fails to understand is that one BIG reason that the Intel compiler is better than GCC is that the same kinds of compiler optimization that accounts for how the hardware schedules things work for both the PPC and the Intel architecture. This has been true since the original entry of the MIPs architecture for goodness sake. Intel KNOWS what the hardware is going to do, and built those smarts into the compiler! You can do the same thing for the PowerPC by the way..not saying you can't.

Nuff said - it was an interesting article but bowed to much towards RISC is Great - All Hail RISC bunch.

Re:Truly suprising colnclusion, OR NOT!

[geirt]

... but he does misses one of the major problems with RISC architectures, the fact that RISC executables are larger that CISC programs (since RISC usually have simpler instructions and fixed instruction length). Today CPUs are fast, but memory are not. Because of this modern computers have large caches, 800MHz FSB, dual DDR memory busses, etc, but still the memory is slow compared to the raw computing power of the CPUs. But since a CISC program is smaller, the memory pressure is lower on a CISC system, and that's one of the reasons way the RISCs don't have the (on paper) large advantage compared to the CISCs.

This was not true 10 years ago, since the memory timing back then was in the 25MHz range, and the CPUs where running 20MHz. Today we have 3.2GHz CPUs and memory at 800 MHz, so program size matters.

Modern ARM RISC CPUs have worked around this problem by adding an extra instruction set called arm thumb, to make the program smaller. Smaller programs = faster execution on the same memory system

dang, somebody better tell intel

[cheezus]

um.... the PDP-11 was an x86?

Law of diminishing returns

[Anonymous Coward]

The Law of diminishing returns is not exactly a new phenomenon, it was originally noticed in parallel computers by IBM engineer Gene Amdahl, one of creators of the IBM System 360 Architecture.

As opposed to economists, thousands of years ago.

A good OS...

[svenjob]

...makes all the difference. The thing that made me switch to PPC was, without an effing doubt, MacOS X. I went from an Athlon 2400+ with 768MB RAM to a home-made PowerMac 800 with 512MB RAM. I cut my processor by a 3rd and lowered my RAM. What did I gain? An amazing OS. If RISC processors continue to get more and more into the same processing spectrum as x86's, I think that OS X will help draw in the masses. Another thing that would help would be increased yields. That would lower prices and increase market share. Anyways, if x86 had OS X, I probably would have stayed with x86. But since it doesn't, I didn't.

Re:how long can x86 go?

[Blob Pet]

Which dies first, BSD or x86?

An interesting viewpoint

[downix]

From my experience with RISC CPU's is that rating them by Mhz is often times the way to not understand what makes a RISC a RISC and a CISC a CISC.

Let me explain by example.

My MIPS R4400, running at around 120Mhz, I believe, runs circles around my Duron 750Mhz machine here. This is while the R4400 uses sDRAM vs DDR-RAM in the Duron, and the R4400 uses older plain-jane IDE while my Duron runs ATA-100.

I find it nice to boot up my old Indigo2 and play around, it responds so nicely, and renders quite well.

Re:An interesting viewpoint

[uradu]

> rating them by Mhz is often times the way to
> not understand what makes a RISC a RISC

What you mean is that you can't compare RISC MHz to CISC MHz--or any design's MHz to any other design's MHz, for that matter. Your statement in fact reveals that YOU don't understand RISC, because MHz are a much more reliable metric for RISC than for CISC CPUs. That is because by the very definition RISC CPUs tend to take a constant amount of ticks per instruction, which is not the case for CISC. So yes, comparing two RISC CPUs that both execute one instruction every two cycles on a MHz basis will give you a pretty good comparison of their relative performance.

Re:An interesting viewpoint

[Octorian]

Ok, that statement is just plain wrong, unless you're comparing something other than CPUs.

First, that Indigo2 is not "plain-jane IDE" (unless you're using some weird adapter board), but rather "plain-jane SCSI-2" (10MB/s).

Second, one big factor you notice when comparing CPUs, especially when some are "budget models" is that magic thing known as cache. Ever wonder what feature they're cutting to lower cost? I'll bet the R4400 has plenty of cache, while the Duron cuts cache (so does the Celeron, and some of Sun's older and slower microSPARC CPUs)

Third, even with those factors, there's no way in hell that the MIPS R4400 (at 120MHz) CPU could ever come close to touching the performance of an AMD Duron (750MHz). You have to be comparing graphics cards.

Now, one of the features of the Indigo2 that you might be using, is the "Impact" line of graphics cards. The Solid (no texturing) and High Impact (texturing) versions have about 450 MFLOPS of performance on the card itself, and the Max Impact has double that. I will believe that your Indigo2 whoops the crap out of the Duron on graphics, if you're comparing one of those fine GIO64 graphics cards to some POS card you threw in the PC.

But I will NOT believe you're comparing CPU performance.

How do I know this? Well, let's just say I've got an R10000 (195MHz) SGI Indigo2 High Impact sitting next to me.

Re:how long can x86 go?

[Elwood P Dowd]

You could say that right now, "The x86 is not dead, because the RISC processors that replace them have a CISC compatibility layer".

The P4 decodes the larger, more complex x86 instructions into smaller chunks for use inside the processor, which is more or less RISC in its core. The CISC vs. RISC debate is kindof over, because both CISC and RISC chips have been adapted to gain the advantages of each others' design principles. Even the PPC 970 has to decode some of its "RISC" instructions into separate micro-instructions for execution.

The only chip design methodology that still has its original meaning is VLIW. That original meaning is "bankruptcy."

[Q] Small & Expensive = CISCRISC?

[4of12]

When Microprocessors such as x86 were first developed during the 1970s memories were very low capacity and highly expensive. Consequently keeping the size of software down was important and the instruction sets in CPUs at the time reflected this.

So I'm puzzled. Perhaps someone can enlighten me on this.

If CISC is particularly appropriate for memory that is

1. low capacity, and
2. highly expensive

why doesn't the same argument apply to CPU's with no main memory per se, but just a good sized L3 cache?

Modern cache memories are, guess what,

1. low capacity, and
2. highly expensive

so it would seem to follow that higher performance could be got by using a CISC model.

Since main memory latency and BW are pretty limiting, I half expect that there's good argument to make very high performance systems live completely inside a large cache.

PPC

[pmz]

Given that electricity is not free, the fact that a PPC-based computer (or almost any non-x86 computer, for that matter) draws significantly less electricity is, well, significant.

If a company spends extra money on a set of gorgeous G5s or whatever, a non-trivial amount of that money is made back on the utility bills for very similar performance.

Other RISC vendors can be a win, also. For example, my old UltraSPARC workstations are not the space-heaters they might be stereotyped as (USII draws less than 20W). UltraSPARC III tops out at 65 watts, which although not as good as the PPC 970 is still much better than P4 or Itanic.

Re:PPC

[ichimunki]

I think you missed his/her point. If the cost of the more energy-efficient processor exceeds the amount of the money saved on the power bills, the company or household is worse off for buying the more efficient model. In the example, the $37 was no match for the $500 extra expense of the system.

Imagine buying a G5 iMac desktop will save me $50/year in electricity bills, but the system costs $200 more than a comparable x86 machine. Then it takes four years for the energy savings to pay for the added equipment expense. Multiplied over 50 workstations, the effect is the same, only the numbers get bigger on both sides of the equation. Just because those 50 machines will save me $2500 annually, doesn't mean they're necessarily worth $10,000 more up front.

However, the energy assumption is a difficult one to make. Energy costs are volatile, generally only increase, and are not an insignificant variable expense for most businesses-- minimizing that expense is not a bad move.

Re:PPC

[JaguarCro]

Around here (Colorado), electricity is seven cents a kilowatt hour.

Well welcome to Northern California where our electricity is currently 24 cents per kilowatt hour! Now here we are talking ($36.69 x (24/7) or $126.14 per year per machine. Apple doesn't sell a dual 1.6 Ghz machine, but if you still use your comparison numbers and prices we get a payoff in less than 4 years. (and if you really were just doing CAD you wouldn't need to Superdrive or Modem which cuts the price difference now down to $270 or almost 2 years!!)

In otherwards, before a/c costs are taken into account the machine will pay for itself in just over 2 years and for the remaining 1 to 2 years it is used it will be saving the company even more money.

By these numbers alone, I would say that buying a PC in expensive electricty areas of the country is a short sided mistake that will hurt your company or institution.

970 is a real superscaler

[norwoodites]

the 970 can have more than 200 instructions in flight at the same time, it can finish up to 5 instructions each clock (4 if there is no branches).

low power? not even close

[JohnZed]

Yup, g4s and g3s use substantially less power than their x86 foes, but the g5 is a different story altogether.

Each g5 dissipates a whopping 97 watts (see http://www.eet.com/sys/news/OEG20030623S0092, which is why the new powermacs have such absurd cooling systems and massive, mostly empty cases. The high-end powermacs actually come with an OUTRAGEOUS 600 watt power supply (http://developer.apple.com/documentation/Hardware /Developer_Notes/Macintosh_CPUs-G5/PowerMacG5/Powe rMacG5.pdf.
Let's be clear, this power supply is not for peripherals: the g5 powermac only supports 3 drive bays and 3 pci slots.

The numbers cited by the author come from an early projection of power consumption for lower-spec ppc970 processors.

Check your facts, please; G5 IS low power

[LionMage]

Each g5 dissipates a whopping 97 watts

No, two G5 (PowerPC 970) processors together dissipate 97 Watts. Each individual processor dissipates about half that.

Don't believe me? Check out this chart on ArsTechnica. (The heading for the chart reads "Preliminaries: die size, power consumption, and clock speed.") A single 1.8 GHz PowerPC 970 dissipates 42 Watts. So a single 2.0 GHz PowerPC 970 dissipates a little more than that; therefore, it's reasonable that two of them would dissipate somewhere between 90 and 100 Watts, total.

The EE Times article you cited is highly inaccurate. They only look at the total number of fans in the G5 machine, and forget the fact that these are low-RPM fans and are software controlled per-zone to regulate temperature. Low RPM means less volume of air moved per unit time. So the design tradeoff that was made, clearly, is to have more fans running slower in order to keep noise levels down and to target cooling for each zone appropriately.

This is why it's a good idea to check multiple sources for your facts. Then again, if your goal was to present a very distorted version of reality to fit your goal of painting the G5 as a power hungry monster, you would very carefully choose your source of information so that it seems to support your assertion.