Battle 2: AMD vs. AMD

Next up on the fight list for today is AMD, competing against themselves. AMD has gained quite a bit of popularity over the past year and needless to say it is because of their extremely strong showing with the Athlon 64. That being said, with three different flavors of Athlon 64s (Socket-754, Socket-939 and FX) and a lot of users still hanging onto their Athlon XPs, AMD's performance breakdown is an important one to look at.

We know by now that Doom 3 is very cache intensive, which in turns means its very memory intensive - bringing us to our first evaluation: Athlon 64 vs. Athlon 64 FX. The Athlon 64 FX once held two advantages over the Athlon 64, a larger 1MB L2 cache and dual channel memory controller. Now with the introduction of Socket-939, the Athlon 64 also has dual channel capabilities but only on newer chips, not the older Socket-754 offerings. As you can guess, there are two comparisons we'd like to make here: Dual Channel vs Single Channel as well as the impact of cache size on performance.

First we'll tackle dual vs single channel memory interfaces; for this test we used a Socket-939 Athlon 64 FX-51 (2.2GHz/1MB L2) as our Dual Channel platform, and a Socket-754 Athlon 64 3400+ (2.2GHz/1MB L2) as our Single Channel platform. You can see that other than the sockets, the two chips are identical, making this the perfect single vs dual channel memory comparison:

Memory bandwidth doesn't seem to be something that the regular Athlon 64 needs much more of, as the move to dual channel DDR400 only offered a 3% increase in performance. At higher resolutions, the performance advantage would become even smaller. We didn't really expect anything different here, as the dual channel memory interface never really helped the Athlon 64 - definitely not as much as it did the Pentium 4.

Next, let's see how cache size influences Athlon 64 performance under Doom 3. For this comparison we have four chips to compare in two separate sets. We use an Athlon 64 2800+ and a Sempron 3100+, both clocked at 1.8GHz but feature a 512KB and a 256KB L2 cache respectively. We also have an Athlon 64 FX-53 and an Athlon 64 3800+, both clocked at 2.4GHz but feature 1MB and 512KB respective cache sizes. While the four numbers are not directly comparable to one another, the two comparisons do give us an idea of improvements due to cache size varying from 256KB up to 1MB on the Athlon 64:

Looking at the Athlon 64 vs Sempron we see that there's barely a 5% performance difference between the two identically clocked chips, indicating that although a 256KB L2 cache isn't big enough for Doom 3 a 512KB L2 cache doesn't help out that much more. The on-die memory controller helps ensure that despite the small cache size, performance remains very competitive with the competition as we will soon see in our fourth battle.

Our 512KB vs. 1MB L2 cache size comparison reveals something interesting: it's not that a 512KB L2 cache isn't big enough for Doom 3 (which is the case with the Pentium 4), it's that the Athlon 64's on-die memory controller effectively masks the need for a large L2 cache in Doom 3. Going to a 1MB L2 cache results in less than a 4% performance improvement, much less than what we saw with Prescott vs. Northwood.

Bottom line: cache size is far less important for the Athlon 64 than on the Pentium 4 as you would expect thanks to the on-die memory controller.

Prescott vs. Northwood Celeron D vs. Sempron
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  • michael2k - Wednesday, August 4, 2004 - link

    Heh, what about frames/$ graphs? Reply
  • Da3dalus - Wednesday, August 4, 2004 - link

    Lovely graphs, *pats my Athlon 64 3200+ while waiting for Doom 3*

    Another week for Doom 3 to hit our european shelves, damnit I hate waiting for something you americans already have :-/
    Reply
  • elfy6x - Wednesday, August 4, 2004 - link

    I have a dual Opteron 246 setup, with 1Gb of ram, and a Radeon 9700 Pro. I'm not really a gamer, but I gave Doom 3 a shot, and it utilizes both of my CPU's when I play. I have nothing else running when I play the game. It doesn't tax both CPU's to 100% but one CPU fluctuates between 40-50% while the other one bounces around 10-20%. So something is processing two threads. Just my observation. :) Reply
  • PotatoMAN - Wednesday, August 4, 2004 - link

    I second the idea of benching memory and video memory at AT for doom week. I have a 3200+ A64 and I am wondering if I am starving it more with a 9800 pro (128) or with my 512mb of RAM. Thanks AT for being awesome! Reply
  • Gooberslot - Wednesday, August 4, 2004 - link

    I bet a 1-1.2ghz P3 or Athlon would cut it for a minimum. Just go back and look at the old benchmarks of the P4 1.5ghz on here. Only in Quake3 was the P4 on top. In UT the P4 actually tied with the P3 1ghz. Pathetic. Stating minimum requirements based on those old Williamete P4's is very misleading. Perhaps the real minimum cpu requirements should have been 1.2ghz P3 or Athlon, 1.5ghz P4, or 2.4ghz Celeron. :) Reply
  • matman326 - Wednesday, August 4, 2004 - link

    Man I always knew that an athlon 64 system was powerfull but a 180 dollar proc. beating Intels Extremly Expensive 1000 dollar proc is just mind blowing. So much for the Netburst design kicking butt. Reply
  • AtaStrumf - Wednesday, August 4, 2004 - link

    If you could find some time, I'd like to see a comparison between 128 and 256 MB R9800Pro, and 512 RAM and 1024 MB RAM. Basicly how much of a difference do video and system RAM make. Reply
  • at80eighty - Wednesday, August 4, 2004 - link

    dammit! looks like im gonna celebrate Christmas with a loan..grrrr... : )
    Reply
  • WooDaddy - Wednesday, August 4, 2004 - link

    Two words:

    AMD ROX!!!


    I've been an AMD user since the 386 days and even had a NexGen processor (pre-pentium, K5). Never went Intel, never will (maybe)...

    Thatsright,
    Naw.. The charts don't lie. But to be fair, let's wait for the Intel-funded people (aka Tom's (blow)hardware) to put up their benchmarks. 10 bucks says they'll make all kinds of excuses to why Intel procs aren't fast enough.
    Reply
  • Regs - Wednesday, August 4, 2004 - link

    Wow. Good info. Dual channel offers nothing. And the socket 939 2.2 Ghz CPU offers nothing over my 3000 A64 which costs 200 dollars less. Given that if you play on higher resolutions. Reply

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