The Dark Knight: Intel's Core i7
by Anand Lal Shimpi & Gary Key on November 3, 2008 12:00 AM EST- Posted in
- CPUs
Turbo Mode: Gimmicky or Useful?
I refuse to make any further references to the Turbo buttons on PCs from the 80s and early 90s in this section :)
Intel's Core 2 processors have historically been quite overclockable, however most users don't overclock and thus they get no benefit from the added headroom in Intel's chips. Enthusiasts obviously benefit and get the performance of the best CPUs at much lower price points thanks to overclocking, but the rest of the world has all of this untapped power sitting under their heatsinks.
Varying clock speed according to system demands and temperature is nothing new, but it's predominantly done in the downward direction. At idle periods CPU clock speeds are dropped, when temperature limits are reached the same also happens, but why not boost clock speed when conditions are ideal?
This is exactly what Intel's Turbo mode does. Originally introduced on mobile Penryn, Turbo mode simply increases the operating frequency of the processor if conditions are cool enough for the CPU to run at the higher frequency. On mobile Penryn we only saw a frequency jump if one core was idle, but with Nehalem's Turbo mode all four cores can overclock themselves if temperatures are cool enough.
Each Nehalem can run its four cores at up to 133MHz higher than the stock frequency (e.g. 3.33GHz in the case of the 3.2GHz 965 model), or if only one core is active then it can run at up to 266MHz higher than stock (3.46GHz up from 3.2GHz).
I measured the impact of Nehalem's Turbo mode on the top bin Core i7-965, which runs at 3.2GHz by default but can ratchet up to 3.33GHz or 3.46GHz depending on whether the workload is single or multi-threaded:
| POV-Ray 3.7 | 3dsmax 9 SPECapc CPU Rendering Composite | x264 HD Benchmark (Pass 1 / Pass 2) | iTunes WAV to MP3 Convert | iTunes WAV to AAC Convert (Single Threaded) | |
| Intel Core i7-965 (3.2GHz, Turbo OFF) | 4017 PPS | 17.1 | 82.7 fps / 30.4 fps | 27.1 seconds | 34.1 seconds |
| Intel Core i7-965 (3.2GHz, Turbo ON) | 4202 PPS | 17.6 | 85.8 fps / 31.6 fps | 26.4 seconds | 32.8 seconds |
| Performance Advantage | 4.6% | 2.8% | 4.6% | 4.1% | 3.8% |
At best we should see a 4ish % increase in performance and the fact that POV-Ray shows us something greater than that tells us that Turbo mode works (and we're within the 1 - 2% margin of error of the test). Surprisingly enough, all of the multi-threaded tests had no problems using Turbo mode to their benefit giving us a 3 - 4% increase in performance thanks to the corresponding increase in clock speed. The AAC iTunes test is important as it is single-threaded, but despite the larger increase in clock speed performance didn't seem to improve any more.
Our Turbo testbed
Now these tests were conducted on an open-air testbench with an aftermarket cooler by Thermalright, we wondered what would happen if we used a retail Intel HSF and stuck the Core i7 in a system with a Radeon HD 4870 and a 1200W PSU. The CPU actually ran a lot warmer and Turbo Mode never engaged, pretty much as expected.
With Nehalem it may be worth investing in one of these oversized heatsinks, even if you're not overclocking, you'll get a couple of extra percent in the performance department if you can keep the cores cool.
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Gary Key - Monday, November 3, 2008 - link
"The 920 to 3.6/3.8 is a nice overclock but I wonder what you mean by proper cooling and how close you came to crossing the 80C "boundary"?"It was actually quite easy to do with the retail cooler, in fact in our multi-task test playing back a BD title while encoding a BD title, the core temps hit 98C. Cinebench multi-core test and OCCT both had the core temps hit 100C at various points. Our tests were in a closed case loaded out with a couple of HD4870 cards, two optical drives, three hard drives, and two case fans.
Proper cooling (something we will cover shortly) consisted of the Thermalright Xtreme120, Vigor Monsoon II, and Cooler Master V8 along with the Freezone Elite. We were able to keep temps under 70C with a full load on air and around 45C with the Freezone unit.
Th3Eagle - Tuesday, November 4, 2008 - link
Wow, thats interesting. Can't wait to see the new article. Always nice to see an article about coolers.Thanks for the reply.
Anand Lal Shimpi - Monday, November 3, 2008 - link
Gary did the i7-920 tests so I'll let him chime in there, we're also working on an overclocking guide that should help address some of these concerns.-A
whatthehey - Monday, November 3, 2008 - link
Tom's? You might as well reference HardOCP....Okay, THG sometimes gets things right, but I've seen far too many "expose" articles where they talk about the end of the world to take them seriously. Ever since the i820 chipset fiasco, they seem to think everything is a big deal that needs a whistle blower.
Anandtech got 3.8GHz with an i7-920, and I would assume due diligence in performance testing (i.e. it's not just POSTing, but actually running benchmarks and showing a performance improvement). I'm still running an overclocked Q6600, though, and the 3.6GHz I've hit is really far more than I need most of the time. I should probalby run at 3.0GHz and shave 50-100W from my power use instead. But it's winter now, and with snow outside it's nice to have a little space heater by my feet!
The0ne - Monday, November 3, 2008 - link
TomHardware and Anandtech were the one websites I visited 13 years ago during my college years. Tom's has since been pushed far down the list of "to visit sites" mainly due to their poor articles and their ad littered, poorly designed website. If you have any type of no-script enable there's quite a bit to enable to have the website working. The video commentary is a joke as they're not professionals to get the job done professionally...visually anyhow.Anandtech has stayed true to it's root and although I find some articles a bit confusing I don't mind them at all. Example of this are camera reviews :)
GaryJohnson - Monday, November 3, 2008 - link
Geez, calling a core 2 a space heater. How soon we forget prescott...JarredWalton - Monday, November 3, 2008 - link
I think overclocked Core 2 Quad is still very capable of rating as a space heater. The chips can easily use upwards of 150W when overclocked, which if memory serves is far more than any of the Prescott chips did. After all, we didn't see 1000W PSUs back in the Prescott era, and in fact I had a 350W PSU running a Pentium D 920 at 3.4 GHz without any trouble. :-)Griswold - Tuesday, November 4, 2008 - link
Funny comparison. If it was just for the space heater arguments sake (well, 150W is by far not enough to qualify as a real space heater to be honest), I could follow you but saying the 150W of a 4 core, more-IPC-than-any-P4-can-ever-dream-of, processor should or could be compared to the wattage of the infamous thermonuclear furnace AKA prescott, is a bit of a long stretch, dont you think? :pRyan Smith - Monday, November 3, 2008 - link
Intel can call it supercalifragilisticexpialidocious until they're blue in the face, but take it from a local, it's Neh-Hay-Lem. Just see how it's pronounced in this news segment:http://www.katu.com/outdoors/3902731.html?video=YH...">http://www.katu.com/outdoors/3902731.html?video=YH...
mjrpes3 - Monday, November 3, 2008 - link
Any chance we'll see some database/apache benchmarks based on Nehalem soon?