Performance Discussion - The Biggest Bottleneck

I wanted to spawn a discussion on system performance. More specifically, what do you think is the biggest bottleneck in a computer system?

These days, we are starting to see diminishing returns for improvements in various hardware. It has gotten to the point where insignificant improvements are taken to be huge leaps in technology. We used to live in a time where the newest video card gave a 20-40% improvement over the competition, whereas today it is more like 5%. CPUs used to give similar increases, and now they, too, are giving < 5% improvements.

So what is the bottleneck? What is preventing our systems from doubling in performance? Is it system memory? Is it the CPU or the video? Is it AGP? Or front side bus speed? Is it the hard disk or removable media? Or is it something else entirely?

Before I give my opinion, I was just curious on what other people thought. So come on... state your opinions. Keep it technical, if you can, and site examples if possible. Web links are really great, too.

As for what's holding up performance on the most general level, I think the answer to that is easy: hard drives. Everything else in a computer is measured on the order of nanoseconds, yet hard drives are still way up in the millisecond range. As long as things like seek times stay up at say 9ms, things won't change much. I mean, the processors will get faster and the computer will be able to crunch more numbers, but in overall use, it won't "seem" that much faster. Unfortunately, I'd consider this to be a limitation of hard drives themselves, i.e. until we get away from mechanical forms of storage, and into the realm of say holographic or other optical storage methods, then things won't get dramatically better.

And the comments about smaller performance increases with succeeding generations of technology...I think that's only partway true. If you look at CPU speeds over the past couple years, processing power has actually beaten the estimate from Moore's Law (due to the chip wars between Intel and AMD). So in that sense, performance is still increasing just as much as before. However, I think the greater scale leads to the impression of diminishing returns. For instance: around 1995, Intel had the 100MHz Pentium. They followed up with chips running at 120MHz and 133MHz, representing increases of 20 and 33%. Pretty hefty. But the numbers themselves are small in comparison to today's chips...it'd be akin to Intel releasing a chip running at 800, then following it with a chip running at 960 (20%) and 1066 (33%). Which of course we know they don't do. In other words, the increments between chips has stayed pretty much the same, but the frequency of their releases has been increased instead (hell, I remember a few years back, it seemed like it took 3 or 4 months for a new chip to be released).

And then of course there's the bigger question: is the extra speed really necessary? For the most part, I'm inclined to think that it isn't. I upgraded my PII 350 to a Celeron II @877 several months ago. To be honest, the differences between the two processors in typical everyday use was negligable at best. To satisfy my own personal curiosity, I even timed how long it took to do certain things on my computer with the two different chips (the results are actually online: http://jpnsystems.8m.com/celeron566/index.html) but it turned out that the new chip didn't make much of a difference at all. And the 250% boost in clock speed only really came into play with things like video compression, where the extra clock cycles can be put to use. The rest of the time, the chip sat on it's *** waiting for the hard drive to catch up.

I'm not sure what the point of all that was https://www.sharkyforums.com/images/.../2005/06/5.gif

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Originally posted by nkeezer:
As for what's holding up performance on the most general level, I think the answer to that is easy: hard drives. Everything else in a computer is measured on the order of nanoseconds, yet hard drives are still way up in the millisecond range. As long as things like seek times stay up at say 9ms, things won't change much. I mean, the processors will get faster and the computer will be able to crunch more numbers, but in overall use, it won't "seem" that much faster. Unfortunately, I'd consider this to be a limitation of hard drives themselves, i.e. until we get away from mechanical forms of storage, and into the realm of say holographic or other optical storage methods, then things won't get dramatically better.

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But hard drives have always been measured in ms and memory has always been measured in nanoseconds...that hasnt changed, they've just gotten smaller(proportionally?). I think its due to the FSB. Think about it, when we had 133mhz pentiums, wasnt the bus speed 66? Im not sure, because the first computer i built was a 233 k6, then before that, i just owned a 486. But a 66 bus speed compared to 133 or 233 is a bigger memory speed to cpu speed ratio than, say 133mhz buss to 1133mhz cpu speed. The problem with just speeding up the bus is the heat issue. Im assuming the chipset would generate gobs and gobs of heat running at 1133Mhz! But if memory/bus/cpu speeds were equal, the proc wouldt have to go into "wait states(??)" waiting for the memory to catch up to itself.

This is all based off of some articles i was reading a year or so back, so it may not all be 100% accurate. Im open to criticizim to it because it is probably partly wrong.


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Compaq Armada E500
650MHz PIII 128MB RAM
8MB ATI rage mobility
11GB hard drive/DVD
dual booting win98/2k

who said you cant game on a notebook????

My point exactly: hard drives as so slow compared to the *other* components in a computer, that huge increases in processing power and the like are effectively covered up (in normal use) by the lagging hard drives. So until we can get rid of spinning platters and other mechanical components as a means of data storage, then hard drives will continue to be the biggest bottleneck.

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Originally posted by zombor:
But hard drives have always been measured in ms and memory has always been measured in nanoseconds...that hasnt changed

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"You have just destroyed one model XQJ-37 nuclear powered pansexual roto-plooker....and you're gonna have to pay for it." -- Frank Zappa

but the hard drive isn't continously being accessed like memory is. it is for loading things like games and programs, then once theyre loaded, it never accesses the HDD for that app again to load it anyway. In game performance has nothing to do with HDD speed(unless your using virtual memory!). although speeded up HDD will increase overall speed, its not really the "limiting reactant" as my chem teacher said today https://www.sharkyforums.com/images/.../2005/06/6.gif

And windows would load 10x faster if all the legacy code for the architecture was destroyed, but thats a whole other topic!

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Compaq Armada E500
650MHz PIII 128MB RAM
8MB ATI rage mobility
11GB hard drive/DVD
dual booting win98/2k

who said you cant game on a notebook????

Limiting factors...Slow refresh rates for monitors at 1600X+ Just wasted FPS...

Parts that work non-asink.

There are current techs on faster hardrives with no moving parts. They use crytal and can store the internet.. heh...joke

If HD's where as fast as dram. Then there would be no point in dram.

I personally think the limiting factors are the Motherboard to hardware parts interfaces..Pci, ISA, AGP...If we had agp slots for all cards...Call it apci?

When the speed of Cpu's have reached there max we will just make duel cpus a standurd. Multi CPu's are what made the super computers that tolk up rooms into those small Doctor Who sized Tartuses..

I dont want the see video cards anymore. I want to see GPU sockets! Adding Alphas to are Video GPU's like we do to new cpu's...Gives a whole new light to onboard video?

I dont want the see video cards anymore. I want to see GPU sockets! Adding Alphas to are Video GPU's like we do to new cpu's...Gives a whole new light to onboard video?

[/B][/QUOTE]

Now that I think about it..Why not add on-die cash to the Gpu's? Hmmmm

HD's are by far the slowest things computers have.. aside from printers https://www.sharkyforums.com/images/.../2005/06/5.gif.
If you want more speed go intp RAID 0. This will impore the speed. Also going SCSI will help, specialy if you get thouse 15,000 RPM Drives.
But for the real boost in performance we gotta wait 'till solid state HD's will get to the market for any1 who has less then a spare million sitting around https://www.sharkyforums.com/images/.../2005/08/2.gif

This is an interesting question https://www.sharkyforums.com/images/.../2005/06/5.gif
I assume we're talking standard PC hardware here.

This very much depends on the sort of application that your running.

For example in my old job I was dealing with 3d scenes containing 100s MB of textures on screen at once and 1000s of polygons. Here the limiting factor for a standard PC was the speed of the AGP bus, even with 4X AGP it was simply slow. If you went to an area where the textures fit in the memory of the card, performance would suddenley increase.
The SGI320 and 540 PCs could texture directly from main memory and performed much more consistently.

I can also claim that memory bandwidth (more important than, but linked to FSB). If I'm running a sorting algorithm on data that will fit in RAM, then my memory bandwidth will certainly limit the speed of execution.

IMHO in normal use the HDD only becomes a limiting factor if you don't have enough RAM. If your limited by the speed of your disk, buy some more memory instead of a new processor.

HDDs do limit performance during startup and for the first time you load an application, but to me these are unimportant as they occur relatively rarely and are not performance critical.

I think of removeable media in the same way. If I install something from CD, for example, I know I'm only going to do it once and then the speed of the CD drive becomes irrelevant.

CPU speed can still be the limiting factor if you are running an application with a very tight innermost loop. If this loop fits the in L1 cache, then the processor will be running nearly flat out. Even if it misses the L1 and hits the L2 cache we can consider the processor the limiting factor as the L2 cache tends to be on die now. It is only if we get a complete cache miss and have to go across the bus to RAM that everything slows down.

So, where have the performance increases been recently?

Advances in CPU are most obvious, along with those in 3D gfx cards. Both have been pushing Moore's Law recently.

Memory bandwidth certainly hasn't improved vastly over the last few years, so in the general case this would probably be my choice. My 'old' P2-400 has exactly the same memory bandwidth as my p3-700 at its default FSB, yet the processor speed has almost doubled.

HDDs have increased in capacity at an astounding rate recently, but have not got significantly quicker in real life situations, especially if lots of seeks are involved.

CD drives have hit a plateau in terms of performance, but DVDs are significantly fastre. I'm not even considering floppy disks https://www.sharkyforums.com/images/.../2005/06/5.gif

In a general situation, I think that memory bandwidth is now the limiting factor in a PC. Advances in this area have been slow, yet memory is used fundamentally in a PC.
woah this has turned into a monster post... enough of my ramblings for now https://www.sharkyforums.com/images/.../2005/06/5.gif


[This message has been edited by Raptor^ (edited October 10, 2000).]

The biggest bottle neck is Microsoft. They keep add new fancy features into the OS and software that we have to learn how to disable. If they would stop adding useless stuff and work for a year or two on increasing performance and removing some bugs I'd be more than happy.

The next bottleneck is system memory, with DDR the situation will be better and will perhaps hold for a couple of years. I hope FC-RAM becomes mainstream until then.

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Originally posted by Ymaster:
Now that I think about it..Why not add on-die cash to the Gpu's? Hmmmm

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On-die cash? https://www.sharkyforums.com/images/.../2005/08/2.gif Would be nice ...
I Guess you mean on-die cache ... they already have this, all graphic cards out there have a texture cache and a vertex cache.

any os on a pc will be just as slow, reletavly, to any windows os. And even with ddr memory, it still wont be even as close to as fast(along with the FSB) as the proc.

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Compaq Armada E500
650MHz PIII 128MB RAM
8MB ATI rage mobility
11GB hard drive/DVD
dual booting win98/2k

who said you cant game on a notebook????

I would have to vote for the system bus. We are still running that relatively slow compared to other devices in the system. You can almost factor HD's out of the equation if your lucky enough to have enough memory. We really need some type of high speed, very wide data bus with very little latency. That would at least put the monkey back on processors somewhat.

$ .02

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Originally posted by Adisharr:
I would have to vote for the system bus. We are still running that relatively slow compared to other devices in the system. You can almost factor HD's out of the equation if your lucky enough to have enough memory. We really need some type of high speed, very wide data bus with very little latency. That would at least put the monkey back on processors somewhat.

$ .02

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Yeah, i have to agree with this. The data still has to travel accross the busto get from component to component.

The thing limiting PC performance is a basic rule of economics. "The law of diminishing returns". Any time you add a new technology you see an immediate jump in performance. Over time the tech is perfected, expanded and extended, but each subsequent change yields smaller gains then the previous iteration of the technology. I may make a separate post about some of these "new" technologies that have allowed processors to keep pace.

A prime example of this would be 3D acceleration. The jump from no 3D to the first 3DFX chips was huge in comparison to the change between generations of GPU's now.

Every once and a while we reach a point where improvements in a given area become so difficult that that area begins to lag behind the rest of the system and changes to the whole system architecture are necessary to compensate. Two (relatively) recent examples of this are Ram and motherboards (I'll talk a little more about motherboards in another post). A lot of the design features we see today are dictated by this limitation so I consider these the limiting hardware factor.

HDD are not really a problem since if you have enough memory most consumer apps only use them during startup or when they save data.

I would also like to add that I disagree with some statements made about moors law. Moore's law is specific to speed and complexity of integrated circuits including MPU's; it says nothing about overall performance. It turns out that increased complexity of MPU's have offset limiting factors in other areas keeping IPC high while clock rate increased. As a result absolute performance has matched or bettered Moore's law, but Moore's law does not specifically address performance.

I would also disagree with the statements that performance gains have accelerated in the last 2 years. This may be true for the x86 world but if you look at the cutting edge of processor design (the highest performing processors) the opposite is true.

i was just thinking about this in class:
what if someone built a PC that was all on die exept for the hard drive off course. Think about it...the proc would have direct access to the gpu, the ram, sound card, everything...sure you wouldnt be able to upgrade it at all, but wouldnt it be alot faster than having to go thru busses to et to everything? Just an idea

------------------
Compaq Armada E500
650MHz PIII 128MB RAM
8MB ATI rage mobility
11GB hard drive/DVD
dual booting win98/2k

who said you cant game on a notebook????

Quote:

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Originally posted by zombor:
i was just thinking about this in class:
what if someone built a PC that was all on die exept for the hard drive off course. Think about it...the proc would have direct access to the gpu, the ram, sound card, everything...sure you wouldnt be able to upgrade it at all, but wouldnt it be alot faster than having to go thru busses to et to everything? Just an idea

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What you refer to has been branded by computer architects as the SoC processor (System on a Chip). SiS is coming out with a form of SoC processor, which has integrated video, sound, northbridge, and southbridge. VIA is making a Cyrix processor with integrated video, sound, and northbridge. Intel's Timna processor was supposed to integrate video and northbridge, and just because that project was cancelled, I don't think you'll see the last of that technology.

Right now, integrating DRAM is a very difficult task. Nintendo has managed to create a platform called the Gamecube, which will be its next generation console, and that will be using integrated DRAM. However, it will only be 24MB. It will take semiconductor manufacturers a long time before larger amounts will be able to be integrated inexpensively. Though, they might start by including a small amount of embedded DRAM (say, 16 or 32MB), to act as an L3 cache, perhaps.

Zombor, what you say is true! Integration is in the future for both high and low performance systems.

but is there that much of a speed increase in these integrated systems? Id think there would be due to the speed jump with moving L2 ondie. And if everything was integrated, nobody better realase a new system every 3.546 days https://www.sharkyforums.com/images/.../2005/06/6.gif

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Compaq Armada E500
650MHz PIII 128MB RAM
8MB ATI rage mobility
11GB hard drive/DVD
dual booting win98/2k

who said you cant game on a notebook????

A few words about Motherboards and Ram.

Up until about 7 years ago motherboard speed kept up with processor speed. This has changed a lot and I'd like to take a few minutes to discuses why. But first some history.

When the IBM XT came out the ISA bus could be used as an expansion port to add additional RAM. It didn't take all that long before RAM outpaced the ISA bus but for many years RAM and Motherboards at least kept up with the FSB of the processor even if it took some latency hits along the way.

Back in the 486 days we first started to see the processors pull ahead of motherboards. Intel had a 50 MHz 486 on the market for some time, but even though a 50 MHz motherboard spec was available the chipsets and boards themselves were almost non-existent. Intel finely got feed up and took maters into their own hands and produces the 486 DX2 50 and DX2 66, the first x86 processors with clock multipliers. (This was also when they got into the chipset business) The first generation of Pentiums did not have multipliers but it didn't take long before they had them also.

The reason why motherboards now require multipliers is size. Electrically speaking they have become huge. I say electrically speaking because in many cases it is better measure electronics in wavelengths instead of inches or cm. The original XT board was physically large by today's standards, something on the order of 50 cm by 50 cm. (I don't feel like looking up the exact numbers but these make my calculations easier)

Using an 8 MHz clock and assuming the signal propagate at .667 c (2X10^8) m/s one wavelength is 200000000/8000000 or 25 m. The board itself is 1/50 of a wavelength across. This is a relatively simple thing to design. Even with harmonics it is unlikely you would have to deal with transmission line effects.

I guess at this point I should explain harmonics and transmission lines. If you want to transmit a square wave of a given frequency it is not good enough to transmit that frequency you also have to transmit harmonics. A harmonic is a sine wave that occurs at specific frequencies relative to the original signal. A square wave has harmonic frequency at multiples of every odd number. You usually require a couple harmonics at least to get a decent square wave.

For example, to get a square wave you would add a sine wave at F1, third harmonic at 3xF1 and the fifth harmonic at 5xF1. Each harmonic is smaller then the one below it so higher harmonics play an ever smaller role in the signal. So you need to allow for frequencies 3 -5 time that of your digital signals.

Transmission line effects come into play any time a signal must travel more then about 1/10 of a wavelength. They cause a number of bizarre effects if not carefully managed, like causing open circuits to act like short circuits; short circuits to act like capacitors, etc.

So on the old XT even the fifth harmonic could travel all the way across the board without having to worry about transmission line effects. A 33 MHz board 33 cm across would be almost 1/20 wavelengths across, but if you are careful with your traces and avoid having any (33 MHz) trace being more the 20 cm you can at least get the full third harmonic and probably most of the fifth so you are still OK.

Consider a modern 133 MHz board that is say 25 cm across. The board is now 1/6 of a wavelength across. At this frequency even your primary frequency may be subject to transmission line effects. You now need to carefully control things like impedance, trace length etc to send digital signals around the board. (These effects start to kick in around 1/10 of a wavelength but don't get into full gear until about 1/4 of a wavelength)

Around this frequency you start to run into other problems as well. If two signals travel different distances the difference in travel time can become important. Imagine having two memory chips far enough apart that one receives a second clock pulse half a clock pulse after the first. By the time they send data back to the CPU the second bit of data from the first chip arrives around the same time as the first bit from the second chip. Not a good thing.

This is what is likely to stop parallel busses from operating faster then about 200 MHz and why the really fast memory like RDRAM or SLDRAM use serial busses.

I think it's the laws of physics that are starting to take their toll on the materials used nowadays. Anyway I've always loved wearing turtleneck sweaters. Why not bottleneck sweaters for computers nerds?

Wwwwhhhhhhhooooooosssssshhhhh! -- that was the sound of 90% of what Moridin wrote flying completely over my head https://www.sharkyforums.com/images/.../2005/06/5.gif But at least he summed it up nicely in the last paragraph, so I think I know what he's talking about now. Enlightening https://www.sharkyforums.com/images/.../2005/06/5.gif

Anyway, I still stand by the hard drive as the biggest bottleneck. Now maybe all you guys ever do with your computer is play games, in which case I guess your HD doesn't matter. But I don't, and (I know this is a shock) a lot of other people don't either. And I know that if I look down at my computer, there's a lot of times when that hard drive light is on those things are thrashing away: like any time I want to open an application that I haven't used for a while, or need to save a file and the entire directory structure has to get listed again, or I want to go to a website and it's reading and writing back to the cache folder, etc. Like I said before, all that takes milliseconds. Which might not seem like that much, unless you consider that everything else the computer's doing is measured in nanoseconds. So in other words...seems to me that every time your hard drive is being used, your computer is being slowed down.

And just one final point: the biggest bottleneck in computers is not really the hard drive, the chip, memory or bus speeds. It's really the average consumer that buys their box at Circuit City and is happy with it for 5 years. If all computer users were a bunch of tech geeks, things would certainly move a hell of a lot faster https://www.sharkyforums.com/images/.../2005/06/5.gif

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Moridin was simply explaining one of the many reasons why it is so difficult to move up speeds on the motherboard. These days in modern electronics, you can easily crank up the speed of ICs to over 1GHz. In fact, in other industries other than CPUs, it is even common to see ICs on the order of 40-80GHz with need technology like SoI or Silicon Germanium BJT transistors. However, once you leave the safe confines of your die, you begin to feel the wrath of onboard electrical wiring.

For the reason Moridin gave, and others, it is very difficult to get wide pathways going in excess of certain speeds. Harmonic noise is just one of the factors you start to have to deal with. The front side bus on the Intel and AMD micrprocessors that people use today have 64bits used for data, and many other bits used for address and protocol. Getting these to run at the speed of a microprocessor is not possible with todays electronics, which is why CPUs have multipliers.

However, getting information to the processor faster than it's going right now is only part of the problem. My opinion of the system bottleneck is that it is a number of things that cause current systems to not perform as well as they can. Processor to memory bandwidth is one of them, and perhaps an important one, too. However, even if you were to give a processor an unlimited amount of free information (in other words, the processor receives information instantly without any latency), it still wouldn't be able to process everything it receives.

Perhaps this sounds a little obvious, but consider how much of a bottleneck the CPU really is. My feeling is that the x86 architecture is the bottleneck. Because of the antique nature of the architecture, it is very difficult to improve upon. I am really looking forward to Intel's new architecture, IA64, because that will be the first new architecture Intel has used in it's main processor line since the 8086.

In the future, I see faster systems doing the following.

1) Moving to IA64, or other non-x86 architecture. This will undoubtably be IA64, but I am opening myself to the possibility that IA64 might fail, and another architecture comes to fill its shoes. On this same topic, we'll call it 1b) Paralellize data. In other words, SMP configurations are good for now, but I see symmetric multiprocessing on the core level in the future. Read another post on this forum for more information, but I believe SMT and CMP to be the future. More paralellized code will also be necessary so that each of the processor cores and threads will be given data 'a plenty to sort through.

2) Integrating everything. Like I said, speed is only found on the die, and as soon as you move off of it, you face nature's wrath. So the solution is to integrate CPU, video, memory, I/O, and the kitchen sink all on to the very same die.

3) Serialize I/O. If you have to move off the chip, it isn't going to be using wide parallel interfaces. Rather, everything will move to high speed serial. Serial can move much faster, and can scale well by adding more channels. Since data from different channels don't have to sync up like in parallel, this gives the designer a lot more room to speed things up.

4) Getting rid of rotating media. Nkeezer is mostly correct in sticking with his argument about hard drives. Frankly, a lot of programs out there are hard drive limited, and there may be even more in the future with all the streaming media that is becoming more common. If we want to speed up hard storage, we have to find a way to create cheap media that is not mechanical in nature. Spinning plates will NEVER reach microseconds of access time, let alone nanoseconds. Unfortunately, technology to do this may be a long ways off.

5) Make outside lines optical. So far, we have seen no cable capable of producing more throughput than optical. However, the disadvantage right now is that you can't bend an optical cable because the photons travelling through the cable will leave the cable if the angle is too great (this is a scientific fact... want to mess up data going to a server? bend the optical cable, if there is one). Once we overcome this, which may be very distant from now, we can start wiring our motherboards, and start connecting to online sources through optical cabling, thus enabling very high speed connections.

These 5 things together will move the industry into the next tier of computer performance. Small changes in one area or another aren't likely to affect much. This is my opinion, at least.

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Originally posted by Arcadian:


1) Moving to IA64, or other non-x86 architecture. This will undoubtably be IA64, but I am opening myself to the possibility that IA64 might fail, and another architecture comes to fill its shoes. On this same topic, we'll call it 1b) Paralellize data. In other words, SMP configurations are good for now, but I see symmetric multiprocessing on the core level in the future. Read another post on this forum for more information, but I believe SMT and CMP to be the future. More paralellized code will also be necessary so that each of the processor cores and threads will be given data 'a plenty to sort through.

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I am not so sure about IA-64 at this point. When I first heard about it I was excited but I am beginning to have a lot of doubts. The premise of IA-64 is to make use of VLIW/Explicit Parallelism to avoid the complexities of out of order execution and hopefully get more parallelism then OOOE can achieve.

OOOE finds parallelism at run time using hardware; VLIW/EPIC finds it at compile time using software. In theory this should make your hardware simple.

In other words it is supposed to be small simple and effective. Somewhere along the way IA-64 became very very complicated. The die size is huge and it is too complicated to run at high speed. This is a very bad way to start for a processor whose primary advantage is supposed to be simplicity. This may change with future versions of IA-64 but while IA-64 was under development a few other things happened.

OOOE was developed and perfected. Improved manufacturing process made more transistors available to chip designers. This meant that deep OOO designs are now much more practical. In fact the OOO components of most processes take up less then 20 % of the die space, so it has become relatively cheep to implement OOOE.

On the other side VLIW/EPIC compilers have not advanced nearly as quickly. Memory latency has increased dramatically. This is worse for VLIW then OOOE because memory latency can't be predicted at compile time. Dependencies generated by memory latency can only be resolved at run time using some form of OOOE.

VLIW/EPIC can look much deeper for parallelism then OOOE provided the compiler is good, but OOOE can react to things like memory latency much better then VLIW/EPIC. Ultimately we will probably see a convergence and most ISA's will be similar

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Originally posted by Arcadian:


1) Moving to IA64, or other non-x86 architecture. This will undoubtably be IA64, but I am opening myself to the possibility that IA64 might fail, and another architecture comes to fill its shoes

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Intel has done a very good job of eliminating the CISC penalty in x86. It is still there, but is quite small. They still have a lot of problems though. IMHO,I think X86 can be competitive for some time yet if it can make the following changes. (Not necessarily easy ones though)

Give the architecture some more registers. I don't know if they need 32 like most RISC machines but 16 are a minimum. Limited registers means more memory operations and a lot less parallelism.

Get rid of the accumulator configuration in the ALU. X86 ALU can only save the result of a calculation to 1 register (the Accumulator) and on top of that the Accumulator is always one of the original operands, so you always destroy one of your values unless you specifically save it to another register. The process of copying register contents, moving them to put them in the accumulator adds extra, unnecessary instructions to the program.

SSE can do most of this on the FPU side so that is a step forward, and now that we have SSE2 which is fully IEEE compliant and can completely replace X87 (SSE could not) a lot of the concerns on the FPU side have been addressed.

Get triadic instructions for both the ALU and FPU. X86 and SSE2 only support 2 operand instructions. They can do things like a=a+b, a=a+c etc (the result must be put into a). Most other ISA's support 3 operand instructions and can do a=b+c+d, a=a+b+c, c=a+b+d (result can go anywhere)

At some point 64 bit operation will be required (for memory access)

These changes, along with a trace cache to remove the CISC decode penalty would bring X86 a long way towards parity with more modern ISA's



[This message has been edited by Moridin (edited October 11, 2000).]

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Originally posted by Moridin:
Give the architecture some more registers. I don't know if they need 32 like most RISC machines but 16 are a minimum. Limited registers means more memory operations and a lot less parallelism.

Get rid of the accumulator configuration in the ALU. X86 ALU can only save the result of a calculation to 1 register (the Accumulator) and on top of that the Accumulator is always one of the original operands, so you always destroy one of your values unless you specifically save it to another register. The process of copying register contents, moving them to put them in the accumulator adds extra, unnecessary instructions to the program.

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The Itanium is able to provide these things. It actually has 128 registers, all 64bit. It also has 128 more floating point registers, and 64 predicate registers. The instructions also accomodate you suggestion regarding the ALU. You say in a previous post that you are having some doubts about IA-64. You shouldn't because it is progressing quite well. Some people are displeased that it has taken so long, but there are the 5 9's of reliability it must attain. In other words, 99.999% uptime. Intel can't release it unless it is at least that stable. Plus, the successor to Itanium, the McKinley is supposed to be a much smaller die, and much faster, too. Intel has a lot in store for IA-64, so I would be very surprised if it doesn't do very well.

Moridin:
You're wrong on some points. The x86 ALU can save to results to all registers for many instruction, not just the accumulator (EAX). You can do stuff like
ADD EBX, ECX
AND EBX, ECX
OR EBX, ECX
SHL EBX, 1
You don't need to use the accumulator for those.
However, many instructions (such as MUL and IMUL (the single operand one)) can only work on the accumulator, but it's mainly the complex instructions (which should be avoided anyway).

And a = b + c + d is a 4 operand instruction. A 3 operand should read a = b + c.