Intel's Dual Core Strategy Investigated
by Anand Lal Shimpi on October 22, 2004 3:09 PM EST- Posted in
- CPUs
The Problem with Intel's Approach
The major issue with Intel's approach to dual core designs is that the dual cores must contest with one another for bandwidth across Intel's 64-bit NetBurst FSB. To make matters worse, the x-series line of dual core CPUs are currently only slated for use with an 800MHz FSB, instead of Intel's soon to be announced 1066MHz FSB. The reduction in bandwidth will hurt performance scalability and we continue to wonder why Intel is reluctant to transition more of their CPUs to the 1066MHz FSB, especially the dual core chips that definitely need it.
With only a 64-bit FSB running at 800MHz, a single x40 processor will only have 6.4GB/s of bandwidth to the rest of the system. Now that 6.4GB/s is fine for a single CPU, but an x40 with two cores the bandwidth requirements go up significantly.
AMD's Strategy
While Intel's current roadmap appears to place dual core on the desktop before it makes its way to the enterprise (other than with Itanium), AMD's strategy is reversed - with dual core appearing in workstations and on servers before making a splash on the desktop.
Overall, AMD's approach simply makes more sense, since the overall performance benefit to dual core on the desktop will be minimal at best but strong in very specific applications and usage patterns. With most desktop applications continuing to be single threaded, dual core will still have to wait until there is more application support before truly being useful on the desktop. Heavy multitaskers and those running workstation applications will appreciate the benefits of dual core, but gamers and most other users will find higher clocked single core chips to be better suited for their needs.
The scenario is exactly the opposite in the workstation and server space, with the applications already seeing huge benefits from going to multiple processors thanks to their multithreaded nature.
When AMD mentions that their K8 architecture was designed for multicore operation from the start, they weren't lying. Each Socket-939 or Socket-940 K8 chip, whether it's an Athlon 64, Athlon 64 FX or Opteron, features three Hyper Transport links (whether they are all operational is another question). In order to create a dual core version of a K8 based chip, you simply remove a single pair of Hyper Transport PHYs, one from each chip, and fuse the two Hyper Transport links together - thus creating a direct path of communication between the two cores, capable of transmitting data at up to 8GB/s (at 1GHz) between the two chips. Update: There is some debate as to how AMD implements dual core in their K8 architecture. The above description was provided by AMD from an earlier discussion but many readers have emailed to point out that the two cores are connected at the SRQ level. We are awaiting official confirmation from AMD as to exactly how their dual core technology is implemented. Update 2:While AMD never got back to us with an official response, unofficially they did confirm that the two cores on a single dual core Opteron die do communicate at full speed and are not connected at the HT level. We apologize for the error.
AMD's performance limitation here will be memory bandwidth, with the two K8 cores sharing the 128-bit DDR memory bus. While we currently don't see a huge performance increase from going to a 128-bit memory bus from a single channel 64-bit interface, the move to dual core will definitely make greater use of memory bandwidth.
AMD continues to list the second half of 2005 as the introduction timeframe for their dual core CPUs, with Opteron coming first and then Athlon 64 FX. Once again, as with all release dates, nothing is set in stone, but right now it looks like that both AMD and Intel are planning on having dual core on the desktop in the same general timeframe.
AMD has yet to reveal what the official specifications of their upcoming dual core desktop products are, but based on roadmaps and what we've seen, it would seem that the first dual core desktop parts will be based on two 90nm Athlon 64 FX cores with a shared memory controller. Interally AMD is referring to this CPU as "Toledo" as we've already published.
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ChronoReverse - Saturday, October 23, 2004 - link
@48And Windows reports 10 threads for the UT2K4 demo. I still know that it's not really designed to take full (by full I mean special) advantage of multithreading.
Chuckles - Saturday, October 23, 2004 - link
#37According to 'top' on Mac and Task Manager on Win XP:
Escape Velocity: Nova - 7 threads
Robin Hood: Legends of Sherwood (Demo) - 5 threads
Airburst Extreme (Demo) - 8 threads
Homeworld 2 (Mac Demo @ 1st mission, 2nd save) - 8 threads
Homeworld 2 (PC Demo @ 1st mission, 2nd save) - 8 threads
All seem to be reporting multiple threads.
Sunbird - Saturday, October 23, 2004 - link
I have a question that just popped into my mind,Will the dual core processors from AMD and Intel technically be two 64bit cores?
If it is, man, you get dual core and 64bit all in one, seems it will be pretty cool (but not those dual core prescotts :P ) when you have both of those steaming away with software written for them.
AdamK47 3DS - Saturday, October 23, 2004 - link
I envision more marketing behind the dual core CPUs than performance numbers to sell these. Most people (as is proven by the responses here) will think their getting double the performance simply because they are "dual cores". Dual cores require multithreading capabilities to truly take advantage of them in a single app. If you're a gamer there aren't very many games out there that are multithreaded. Even most games coming out in the next couple years won't be multithreaded. Multithreading can be cumbersome to programmers.AdamK47 3DS - Saturday, October 23, 2004 - link
Reflex - Saturday, October 23, 2004 - link
Just to make one thing clear: I like dual core, I think it is a good move, I can't wait to get mine...However, you will not see 100% improvement on a dual core system, not even close, even with multi-threaded apps. At best you will see 80% in *some* situations, in most circumstances its more like 40-50%. The thing to remember here is that those dual cores are sharing the rest of the system with each other, so a straight 100% improvement is impossible due to the fight for system memory and resources. This is exacerbated on shared bus designs like the P4, but even in the case of the Athlon64 there are some shared resources..
xsilver - Saturday, October 23, 2004 - link
#42 I think you answered your own question"Within a year or two, you will be buying (essentially) 6 to 8 GHz CPUs, instead of 3 to 4 GHz CPUs."
Essentially this 6ghz cpu is no better than the 3ghz cpu on one program -- its all fine and dandy to be able to run 2 programs just as fast with no performance hit but when advertisers say it runs X fast, that X would not have changed; only you can run X and Y at the same time.... Its not double performance, its more like HT overdrived.... you mention MMX, sse etc. they are good features cause they add no cost/ heat into the equation whereas dual cores may double the processor on both counts here...
The INTEL spin doctors though will spin it so it sounds good until software can use the multithread properly...
theprofessor - Saturday, October 23, 2004 - link
I don't know why everyone seems so against dual core CPUs. I have been waiting years for this (as I was for 64-bit CPUs). Most people will see an increase in performance using a dual core CPU. I don't care if the program is single threaded or not. Most people run more than one program at a time. All modern Operating Systems (including XP) will allocate time on both cores for different processes. So, while you’re playing your single threaded game on one core, you can run your encoding software, anti-virus software, im software, e-mail software, download software, whatever software on the other core, with no hit to performance. If you don’t play games, include whatever single threaded software you like. There will be a decent boost to performance no matter what you are doing.Dual core is the best upgrade a processor can get. Why? Because with MMX, SSE, SSE2, 3D Now!, and, especially, 64-bit, there needs to be re-programming and/or re-compiling involved to notice any difference at all. With dual core you will notice a difference in almost all modern computing paradigms the day the chip is released. And as the technology becomes more mature and prevalent, you will notice even more performance as developers re-program/re-compile there software.
Computer enthusiasts should be looking at this as a doubling of computing performance. Within a year or two, you will be buying (essentially) 6 to 8 GHz CPUs, instead of 3 to 4 GHz CPUs. As far as pure performance increase, I think this could be the greatest technology ever introduced to a processor line. No other technology (listed above – MMX, etc.) has been able to give almost 100% performance increase (theoretically) across the board in all applications.
If nothing else, think of it this way. With the ramp in CPU frequency drastically slowing over the last two years, going forward it will now be at least double what it would have been. (i.e. If AMD and Intel can currently only handle 200 – 400 MHz frequency increase in a year, with dual core that becomes 400 – 800 MHz.)
It’s a win almost every way you look at it. So please, try not to be so critical of this great technology.
Thank you
Reflex - Saturday, October 23, 2004 - link
#37: If that were true then every ported PC game would take years to rewrite and bring to the Mac since they are not designed multi-threaded in the first place(and most Mac games are PC ports).Don't confuse the fact that you can multi-task while playing a game with the idea that the game itself is multi-threaded. They are not the one and the same, and you can multi-task while playing a game on Windows as well...
thermalpaste - Saturday, October 23, 2004 - link
Intel could have launched the dual core using the P6 architecture as in the pentium-M processor. If they still love high clock speeds, maybe they can deepen the pipelines a bit for the p6. With prescotts touching 65 degrees plus, the dual cored pentium-4s may need car radiators in order to overclock;). Its obvious that the dual cores only come into play for multi-threaded apps, so perhaps intel can shift back to p6 when majority of apps support multi-threading.