Intel Core i5 And Core i7: Intel’s Mainstream Magnum Opus

Windows 7: Microsoft Listens To Intel, Finally

Over the course of its life, Windows Vista has taken a load of abuse—much of which is deserved.

One area we’ve seen both Intel and AMD affected is power management. In AMD’s case, enabling Cool’n’Quiet technology on its original Phenom processors caused a sizable performance hit as Vista’s scheduler moved threads from active to idle cores running at half-speed in a process called migration.

Cores parked

Why did it do this? In order to maintain the symmetry of a system under full load, you don’t want I/O to become dependent on just one core. If you keep threads rotating between cores running at their maximum performance (this whole concept goes out the window when you start talking about spinning cores down), you get better responsiveness.

This was an implementation decision made during Microsoft’s Windows NT kernel design, and based on our experiences with both processor vendors' hardware, it wasn't considered a "feature" to either company. Of course, it affected Intel in a much different way than AMD. The problem Intel had in Vista was one of power consumption. For every migration, you have to write-combine the Nehalem architecture’s L3 cache, which costs power.

And loaded

This changes with Windows 7 and a feature called ideal core. If a task’s needs are being addressed by one core, the operating system will let you stay there. This means two things to Intel: first, you don’t use power on the migration, and second, idle cores are able to remain in a C6 state. Purportedly, this migration fix alone will yield an extra 10 to 15 minutes of battery life on Nehalem-based notebooks, though this won’t become a major issue until the mobile dual-core Arrandale launches later this year. Perhaps more interesting, though, is that processors without C6 will not realize this gain (including AMD’s CPUs).

Core parking is a second optimization, based on the observation in previous operating systems that you might have four cores running background processes at 10% utilization each. The idea is to load all of those tasks onto one core and let the others idle if operating load levels allow for it. Now, you can see how these two features working together might have a significant impact on power, as ideal core prevents rabid thread migration, while core parking optimizes loading. Taken together, the pair intelligently maximizes the number of idle cores, and then keeps them from being spun up unnecessarily, yielding the theoretical power gains.

If you want to know more about the changes incorporated into Windows 7, check out this interview with Mark Russinovich, a Technical fellow for Microsoft.

We’re Making The Switch

Based on reader feedback to Windows Vista, access to the final Windows 7 code, and great app compatibility with our current benchmark suite, we updated as many software versions as possible and made the leap to Windows 7 for our review here (along with the gaming analysis of CrossFire and SLI graphics configurations, published separately).

But before we did, we wanted to quantify these power-saving claims from Intel for ourselves. So, we logged runs of PCMark Vantage on clean drives with an install of Windows Vista updated to Service Pack 2 and the Windows 7 RTM code, both x64 builds.

The results were actually counter to what we expected. The Windows 7-based build averaged six watts higher over the course of its run, but finished the test three minutes faster than the Vista machine. Also noteworthy, though, is that when the Windows 7 machine has a chance to idle (which is where we'd expect to see ideal core and core parking actually having an effect), it does dip down lower than the Windows Vista box.

We checked these results over with Intel, and came away with the following interpretation: the Windows 7 P-state promotion policies are more aggressive than Vista's, meaning a Windows 7 system ramps to Turbo Boost faster, resulting in the better performance and higher power consumption. At idle, the previously-discussed features enable the Windows 7 config to dip below the idle power draw of the Vista machine.

Overall, though, Windows 7 actually averages higher power consumption in this experiment, even if it simply idles for the three minutes while the Vista box finishes its run. We are fairly certain of why, exactly, this is, but will hold off on comment until we're able to present power data substantiating the claim. However, that doesn't change the fact that, in this case, Windows 7 won't be cutting your power bill. In order to show Windows 7 cutting consumption, we'd have to spend a lot more time at idle (admittedly more representative of how most PCs are typically used), replace a certain component, or disable certain settings in the OS.

Chris Angelini
Chris Angelini is an Editor Emeritus at Tom's Hardware US. He edits hardware reviews and covers high-profile CPU and GPU launches.
  • caamsa
    Dang! AMD better get their $4iT together. Now I need to decided between i7, i5 or phenom II when I do my next happens too fast. Looking forward to more reviews on the i5 and mb prices.
  • People need to be careful when comparing the i7-870 to a i7-920, alot of people pre-release were worried that the 1156 platform was going to dominate the 1366. However when you see the 870 out perform the 920 people need to remember that a 870 is double the price of a 920, and even when you factor in a motherboard a 920 setup comes out cheaper than a 870.

    Now the i5 750 on the other hand is great performance at a great price, and would certainly be the budget gamers new weapon of choice.

    I currently have an i7-920 setup which is my main rig and am very happy with it and not at all upset to the see the 870 outperform it (since the 870 would cost me twice as much). I also have had an i5 750 setup now for over a week (the 1156 processors and motherboards have been available here in Australia for nearly 2 weeks now) and it is an amazing processor for the price of it.

    So what am I trying to say? 1366 is still a good platform for the top end of the market. The i5 are fantastic new processors for their price, and the 1156 i7's are just confusing and I'm not really sure who they are going to appeal to? I could understand it if Intel launched the 1156 i7's in 6months time when alot of users are already using the 1156 platform and are looking to upgrade their CPU without a new mobo. But to anyone looking at getting a 870, just get an 920 and use the extra cash on the mobo and ram to go with it.
  • Nintendork
    A little confusing the charts.

    I would prefer a bench with HD4890. They scale better in CF.
  • aspireonelover
    I can tell, I'm gonna fall in love with the i5 processor
  • cabose369
    Intel needs to come up with a simplified naming system for their products. They are as bad as NVIDIA is right now in terms of naming their products.

    There is sooo much to learn and there is so much information here.... I feel confused!!
  • alikum
    Well, I just hope that the Core 2 Quads will drop in prices significantly so that I could grab the high-end one for my final LGA775 upgrade!
  • buzznut
    Well this is good news for consumers. I'm not certain why it took so long for Intel to make some mainstream proc like i5, but for intel fans it seems worth the wait.
    This will also compel AMD to bring some more value to the market. Nice article.
  • jawshoeaw
    damn, 150 watts at idle?? Is that just the cpu? I hope the gaming rigs built on these processors are not left on 24/7. My old AMD X2 3800 system including the monitor uses less than 150 watts at idle (50 of which is the 22" LCD).
  • unclewebb
    i7 Turbo is a good tool to monitor the multiplier of Core i5/i7 CPUs.

    It uses the method that Intel recommends in their November 2008 Turbo White Paper.
  • evolve60
    "Intel Core i7-920 Extreme (Bloomfield) 2.66 GHz, LGA 1366, 4.8 GT/s QPI, 8 MB L3, Power-savings enabled"

    Since when has the I7-920 become an extreme?