Intel Pentium 4 6xx and 3.73EE: Favoring Features Over Performanceby Anand Lal Shimpi & Derek Wilson on February 21, 2005 6:15 AM EST
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Twice the Cache - 17% Higher Latency
Both the Pentium 4 6xx and the new Extreme Edition share the same core, meaning they also have the same L2 cache. When Intel first launched Prescott we noticed that in the move to the new architecture that cache latencies went up tremendously. The increase in cache latencies was to be expected, as one tradeoff of a larger cache is that it takings longer to find and access data. So when we heard that Intel was moving to a 2MB L2 cache with the 6xx series, we wondered how much slower the cache would get.
First we wanted to confirm that L1 cache latencies stayed the same, and they did at 4 cycles for the new Prescott 2M based core:
|Cachemem L1 Latency||ScienceMark L1 Latency|
|AMD Athlon 64||3 cycles||3 cycles|
|Intel Pentium 4 (Northwood)||1 cycle||2 cycles|
|Intel Pentium 4 (Prescott)||4 cycles||4 cycles|
|Intel Pentium 4 (Prescott 2M)||4 cycles||4 cycles|
|Intel Pentium M||3 cycles||3 cycles|
Next up, was L2 cache latency. In our review of the Pentium M processor on the desktop we discovered that its 10 cycle L2 cache was responsible for its solid performance in non "media rich" applications (e.g. office applications, OS performance). The original Prescott had a 23 cycle L2 cache, and with a 2MB cache the latency has gone up to 27 cycles:
|Cachemem L2 Latency||ScienceMark L2 Latency|
|AMD Athlon 64||17 cycles||18 cycles|
|Intel Pentium 4 (Northwood)||16 cycles||16 cycles|
|Intel Pentium 4 (Prescott)||23 cycles||23 cycles|
|Intel Pentium 4 (Prescott 2M)||27 cycles||27 cycles|
|Intel Pentium M||10 cycles||10 cycles|
While we're talking about "only" 4 cycles, at 3.6GHz that's 17% longer to access data from L2 cache. Given Prescott's extremely lengthy pipeline, a 17% increase in L2 cache latency is not going to help minimize the downsides of such a long pipeline. Also keep in mind that the only architectural change here is a larger L2 cache, so none of the normal tricks to help hide memory latencies are expanded upon in the new Pentium 4.
What Intel is counting on is that the increase in hit rate provided by a 100% larger cache will outshine the 17% longer access to L2 cache. Did Intel make the right bet? In order to find out we took the new Pentium 4 660 (3.6GHz - 2MB L2) and compared it to the old Pentium 4 560 (3.6GHz - 1MB L2), with all other variables the same, let's see how much of an impact the extra megabyte of cache has in the real world.
In the business category, we see the added cache paying off a little. SYSMark shows good improvement in the document creation portion of its tests, while the Business Winstone makes some very good gains. Worldbench shows web browsing with Mozilla to have improved a good bit while our compression test and the ACDSee test show a loss in performance. These losses generally indicate areas where the test is more dependant on latency than cache hit rate. On the content creation side, adding Windows Media Encoder to the Mozilla test improves performance more than the individual Mozilla test. This is likely due to the fact that the large cache keeps Mozilla's data from being kicked out while Windows Media Encoder is working.
On the gaming front, Doom 3 is the only test we saw with any performance improvement. And the only other application to show a significant performance gain is Maya with more than a 43% gain. The huge gain in performance under Maya is likely a result of 1MB of cache being too small to fit models in while 2MB is enough. This seems to be a case where the test is very bandwidth sensitive rather than latency sensitive. Dropping most (if not all) of the data being worked on into the L2 cache offers a program a very large boost in apparent bandwidth.
As we can see, the unfortunate truth for performance on the 600 series is that most consumer data sets can fit into a 1MB cache just fine. The added cache does seem to help with multitasking from our limited investigation of the subject. The more threads that hit memory aggressively, the better chance we have of seeing a benefit from the 2MB cache. This is because less data from each thread will be kicked out of the cache, resulting in fewer pipeline stalls.
Unfortunately, most usage models that are a good fit for the 600 series are server and workstation workloads. Streaming data (using or encoding media), games, and most other consumer applications don't have the lots of big data requirement that can really separate the performance of the 1MB and 2MB parts.
As we've provided this chart and gone through the general impact of the benchmarks on Intel's new 600 line, we won't include analysis on the pages with our benchmark data. For those who are interested in a deeper look at the numbers and performance of all 5 new parts, graphs of each benchmark are included later in this article.
|Impact of L2 Cache Size on Performance (1MB vs. 2MB - 3.60GHz)|
|1MB L2||2MB L2||2MB Performance Advantage|
Business/General Use Performance
|Business Winstone 2004||21.4||24.2||13.0%|
|SYSMark 2004 - Communication||137||137||0.0%|
|SYSMark 2004 - Document Creation||201||218||8.4%|
|SYSMark 2004 - Data Analysis||184||186||1.0%|
|Microsoft Office XP with SP-2||522||520||0.3%|
|ACD Systems ACDSee PowerPack 5.0||547||558||-2.0%|
|Ahead Software Nero Express 184.108.40.206||545||550||-0.9%|
|WinZip Computing WinZip 8.1||412||411||0.2%|
Multitasking Content Creation Performance
|Content Creation Winstone 2004||32.7||33.9||3.7%|
|SYSMark 2004 - 3D Creation||231||231||0.0%|
|SYSMark 2004 - 2D Creation||288||279||-3.1%|
|SYSMark 2004 - Web Publication||206||203||-1.0%|
|Mozilla and Windows Media Encoder||676||601||11.1%|
Video/Photo Creation & Editing
|Adobe Photoshop 7.0.1||342||342||0.0%|
|Adobe Premiere 6.5||461||468||-1.5%|
|Roxio VideoWave Movie Creator 1.5||287||276||3.8%|
|MusicMatch Jukebox 7.10||484||470||2.9%|
|Microsoft Windows Media Encoder 9.0||2.57||2.56||-0.3%|
|Discreet 3dsmax 5.1 (DX)||268||266||0.7%|
|Discreet 3dsmax 5.1 (OGL)||327||329||-0.6%|
|SPECapc 3dsmax 6||1.64||1.62||-1.1%|
|SPECviewperf 8 - 3dsmax-03||17.04||17.11||0.4%|
|SPECviewperf 8 - catia-01||13.87||13.57||-2.2%|
|SPECviewperf 8 - light-07||14.3||13.83||-3.3%|
|SPECviewperf 8 - maya-01||13.12||18.85||43.7%|
|SPECviewperf 8 - proe-03||16.7||16.5||-1.2%|
|SPECviewperf 8 - sw-01||13.09||13.33||1.8%|
|SPECviewperf 8 - ugs-04||15.31||13.82||-9.7%|
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stephenbrooks - Monday, February 21, 2005 - linkThe 3.73 EE was at one stage referred to as the "720" model number. Anyone hear anything more of this? The '20 means 14x multiplier but 14x(1066MHz/4) = 3.73 GHz, so if a 730 was released it would be 4 GHz and so on.
sphinx - Monday, February 21, 2005 - linkI liked the way the info was put into the tables, instead of images. Just an opinion.
jmke - Monday, February 21, 2005 - linkGreat article @ Anandtech, like the power ratings @ LOAD ;)
here's some OC results from X-Bit labs: http://www.xbitlabs.com/articles/cpu/display/penti...
I've also seen 3.0Ghz 6xx series OC to 4.3 with STOCK COOLING!!!
nourdmrolNMT1 - Monday, February 21, 2005 - linkDranzerk, SLI is not stupid. EE is a marketing gimmick to bring money in, you do what you can do to make money. SLI is a smart thing, but back on subject. i think O/Cing has nothing to do with a processors appeal, they are doing the review for those who want to know what intel is up to, not what it can O/C.
Dranzerk - Monday, February 21, 2005 - linkEE is what SLI is to nvidia. stupid.
mlittl3 - Monday, February 21, 2005 - linkIs it just me or is the EE procesors just a big scam? All of the game benchmarks show the 3.46 beating or tieing the 3.73. How can a reputable company like Intel fool consumers with that crap? I want the names of everyone who buys an EE based Dell XPC so that I can tar and feather them in the public square.
I bet I can sell Amway to all those people. :)
mongoosesRawesome - Monday, February 21, 2005 - link"What Intel is counting on is that the increase in hit rate provided by a 50% larger cache will outshine the 17% longer access to L2 cache."
Should be 100% larger cache...
AtaStrumf - Monday, February 21, 2005 - linkOne thing you completely left out of the conclusion, but I think you should definately add is:
Don't buy Intel until they have a chipset out that will support dual core.
danidentity - Monday, February 21, 2005 - linkNice article, but why no overclocking results? That's very dissapointing.
Surely you have a P5AD2-E to test these new chips with.
nourdmrolNMT1 - Monday, February 21, 2005 - linkwhoa.... i got something right.