Where does 64-bit help?

Although the performance that will sell the Athlon 64 today has nothing to do with this, the 64-bit part of the equation will definitely play a role in the processor's future. With no final release of the 64-bit version of Windows XP, there is no popular OS support (we will touch on Linux support as well as Win64 support shortly) and no real application support at this time, but where will the 64-bitness of the Athlon 64 help?

There are three main categories that you can split up the performance benefits into: 32-bit applications running on a 32-bit OS, 32-bit applications on a 64-bit OS and 64-bit applications on a 64-bit OS; we will be analyzing each one of these scenarios individually.

Case 1: 32-bit apps under a 32-bit OS

At the launch of the Athlon 64, the predominant operating environment will be running 32-bit applications under a 32-bit OS. All performance benefits the K8 architecture will show here are courtesy of the on-die memory controller, improved branch predictor, higher clock speed and more robust TLBs - none of the performance improvements you'll see in this case will have anything to do with the 64-bit capabilities of the processor.

Case 2: 32-bit apps under a 64-bit OS

When Windows XP 64-bit Edition is officially released (a public beta is due out at the time of publication), many users will be running their 32-bit applications under the 64-bit OS.

Outside of the performance improvements that we just outlined in Case 1, there are a couple of additional benefits the Athlon 64 may offer users. Currently under Windows, although you have a physical memory limit of 4GB, any given process can only use up to 2GB of memory; the remaining 2GB is reserved for use by the OS. With the 32-bit applications under a 64-bit OS scenario, each 32-bit application could be given a full 4GB of memory to work with, instead of being limited to the 2GB Windows process size limitation. Unfortunately this benefit isn't really "plug 'n play" as the application would have to be aware that it can use the added memory, which in the vast majority of cases would require a new patch to be made available.

The second benefit the Athlon 64 could offer in this scenario comes from the availability of additional registers. Although the 32-bit application would still only be compiled to use the regular set of 8 general purpose registers and standard set of FP and SSE2 registers, the 64-bit OS would be able to reference and use all of the registers at its disposal. The performance benefits that you would see here exist in any sort of task handling that the OS would be doing (switching between applications) as well as just regular Windows performance. Granted that the performance improvements seen here should be negligible, considering the extra overhead that does exist when running 32-bit applications in a 64-bit environment (more on this in a bit).

Case 3: 64-bit applications under a 64-bit OS

The final scenario is the one that shows the most promise, yet has the least amount of application support today - running a 64-bit app under a 64-bit OS. Here, the benefits are numerous; not only do you get the performance improvements courtesy of the Athlon 64's architecture, but each application now has full access to the increased number of registers and each application can use much more than 4GB of memory.

Although the Athlon 64 can support 64-bit memory addressability, for demand reasons it only supports 40-bit of physically addressable memory - or ~137GB, not exactly a limiting factor at this point.

The performance improvements developers are expecting to see under this final scenario has been estimated to be in the 10 - 20% range in tasks that are not memory bound, meaning those areas where the application is using less than 2 - 4GB of memory in the first place will still see sizable performance gains courtesy of the availability of more registers. We will investigate a few of these scenarios to substantiate (or refute) these claims later on in the article.

Performance improvements where you are memory bound will be even more impressive; just think about how slow swapping to disk is and how much faster keeping everything in memory makes your computer.

An Early Christmas present from AMD: More Registers AMD's Gem: Athlon 64


View All Comments

  • Anonymous User - Friday, October 17, 2003 - link

    In response to anonymous "Intel Boy" (biased, biased, biased) you can be in love with Intel if you choose. My experience has been that AMD processors have always been smother running and they run cooler than Intel which increases processor life. The AMD64 is in its infancy. It will get better in the months to come. Reply
  • Anonymous User - Wednesday, October 08, 2003 - link

    sorry I mean#107 Reply
  • Anonymous User - Wednesday, October 08, 2003 - link

    To #117 you wrpote is totally truth but do u think a lot understand it ? thanks anyway :)) Reply
  • Anonymous User - Monday, October 06, 2003 - link

    For #4 and other intel fan boys.
    I understand that you are in furious, you think as chip costs higher it is better and you paid much more money for intel and what? It usually is deafeted by AMD again and you feel sorry especially after the scandal with BAPCo where became clear that BAPCO is witing benchmarks for intel to show tham in better lighte heh even in sys marks 2002 which is "broken" and AMD doesn't recognize this bench even in this test which must not be used by anand athlon51fx is better than 3200EE of intel. and I can't understand how u can defend Intel when thic processor has 3.2 Gghzs and is DEAFETED BY 2200Gghz ? more than 1.2 Gghz handicap. I'll never bye intel even in due of this caus here is clear for even the dumbiest donkeey which technologie is better. thats why real computer specialists always prefare AMD and love tham.
  • Anonymous User - Friday, October 03, 2003 - link

    These benchmark figures appear as if the P4 was used in a single channel setup. Does anybody know if this is correct? Also, ECC DDR-400 chips are very hard to come by, prohibitively expensive, and aren't available with low latencies. I don't think FX systems will be price competitive. What good is the high memory limit when you can only afford 512Mb, or a fast CPU with C3 memory? Too bad. Reply
  • Anonymous User - Friday, October 03, 2003 - link

    Hi, this is about your Athlon 64 Vs. Pentium 4 article, specifically the use of Quake3 as a CPU benchmark when comparing AMD vs. Intel cpus, as shown on this page


    Let me say the article is great, no complaints there. I know it takes alot of work to produce these articles.

    Now, I see two reasons for using a game as a cpu benchmark:
    1) It presents a fair (emphasis on the word 'fair') comparison of the competing cpu architectures and scaling issues.
    2) The game itself is of current interest to the community.

    In your article you already concede 2). Quake3 itself is not relevant as a game to anybody. Quake3-derived games are another matter, and are still popular and certainly relevant. More on these later.

    I believe there is strong evidence that Quake3 does not provide a fair benchmark for comparing *modern* (AthlonXP and possibly Athlon64 as well) AMD cpus vs Intel cpus. The reason being (and let me emphasize that I don't know this as an verified fact, I'm going on what a couple of programmers involved with helping AMD produce optimized game code have told me) that the Quake3 cpu recognition code does not recognize the AthlonXP as an SSE-capable cpu. Not only that, but the 3DNow code in Quake3 is apparently non-functional for this cpu.

    The politics and history behind this are interesting, but probably boil down to the AthlonXP being released well after Quake3, and Carmack being rightly uninterested in patching an old game.

    If this is true, you are benchmarking two equally SSE-capable cpus against each other, using a game engine which enables SSE for the Intel cpu and *disables* SSE for the AMD cpu (apparently there's no simple way to force SSE recognition either), for no valid reason, other than the game is too old to know about the AMD cpu's capabilities. What would be even worse is if this same recognition problem carries over to the Athlon64 (I have no word on this) and to newer Quake3-based games.

    Again, assuming this is true, it removes any rationale for using a 3-year old game that: a) few people play, b) which gives ridiculously high scores, and which c) unfairly handicaps AMD cpus; as a benchmark to be used specifically in comparing AMD cpus vs their Intel competitors in articles such as this one.

    So. Here are the recommendations I, as an interested Hardocp/Anand/Toms reader (and admitted AMD fan) am making to you and your site:

    1) Investigate this matter further, and write an article discussing it. And in particular discuss the relevance of this cpu issue to current Quake3-based games. Assuming there is in fact an Intel bias to Quake3-based benchmarking I think people would be very interested to learn about it. Apparently the SSE issue does indeed carry over to later games.

    2) Assuming there is a bias, discontinue using Quake3 as a cpu benchmark, and especially discontinue it's use when comparing AMD vs Intel cpus. The game will never be patched to fix this issue, and using 3rd party fixes noone cares about is more or less pointless too. I'm referring to the dlls on this page:

    This guy is one of the programmers I referred to earlier, and he tells me the dlls do not enable SSE where it really matters anyway. The other was a student working at AMD writing assembly 3DNow code. The best solution is simply to retire this benchmark, just as Q1 and Q2 were retired.

  • Anonymous User - Thursday, October 02, 2003 - link

    Not to be a ball buster, but in your paragraph:

    "For starters, at a 192mm^2, the Athlon 64 and Athlon 64 FX are well above AMD's "sweet spot" for manufacturing. When we last talked with AMD's Fred Weber, 100 - 120mm^2 die size is ideal for mass production given AMD's wafer size, yields and other manufacturing characteristics - and the Athlon 64 is close to twice that size"

    If you calculate it out, the 64FX is closer to 4x the die size of the "sweet spot". 192mm x 192mm = 36864 sq mm. The "sweet spot" is 100mm x 100mm = 10000 sq mm. Sorry, just figured I'd point that out.

  • Anonymous User - Wednesday, October 01, 2003 - link

    don't hold your breadth1 as far as ms is concerned the visual studio compilers is still not truly 32 bit let alone be 64 bit. without such compilers you cannot get 64 bit apps

    Even Winxp so claimed to be redisigend from bootom up is not true. Well its desigend from broken pieces on the ground hurriedly glued together. How come you still have a System and a System32 folders in c:\Windows??? Thats the 16bit and 32 bit DLLs. Why the sudden Blue scren of death? Same old problem - confilcts between DLLs.

    Try writing code in Visual STudio and query the WinOS ver - for WinXP you will get WinNT as the response. HOw can a truly ground up redesigned OS behave as such? Beats me?

    Until such time that WinXX OS is truly 32bit or 64 bit you cannot have any true 64 bit apps running.

    The BIOS also have problems. nFOrce2 still buggy and not properly fixed - can you trust nForce3? If those guys cannot fix up nForce2, then nForce3 is gonna have lots more problems.
  • Locutus4657 - Tuesday, September 30, 2003 - link


    On what exactly are you basing your arguments? You obviously have no experience or knowledge of Win64... If you did you'd realize 64 bit versions of Windows NT date back to NT4 on DEC Alpha hardware... You obviously have no clue what so ever... Try posting a relevant argument next time... Try something based on benchmarks, and heck, next try even putting it into context as to how you use your computer...
  • Anonymous User - Monday, September 29, 2003 - link

    all i know is i bought amd stock for less than $5 a few months ago and it's on the way to tripling in value. perhaps i'll use the profits to buy another one of their chips. Reply

Log in

Don't have an account? Sign up now