AES-NI: Much Faster Encryption & Bitlocker Performance

Westmere (and thus Clarkdale) adds some new instructions to x86, although the big expansion comes with AVX and Sandy Bridge next year. Westmere gets six new encryption/decryption instructions. The group of instructions accelerate AES (Advanced Encryption Standard) and are thus referred to as AES-NI.

Many businesses require that all corporate PCs have the contents of their hard drives encrypted through the use of software like Bitlocker that comes with Microsoft Windows 7. These sorts of applications can be accelerated by AES-NI and to show the potential benefit I dug up a test I did while preparing for one of our SSD articles several months ago.

If you turn on Bitlocker in Windows 7 there's an immediate and measurable impact to performance. Disk performance generally drops by a noticeable amount and actual application usage performance drops by a smaller amount. Every write to the disk has to be encrypted first so there's some obvious CPU overhead. Clarkdale should reduce that overhead significantly as the common encryption operations are now hardware accelerated.

To test this I ran three tests. I first ran PCMark Vantage's HDD suite on my Windows 7 testbed SSD (an OCZ Summit) on a Core i5 661, then encrypted the drive using Bitlocker and ran the same test on the same processor. For the last test I swapped out the i5 661 for a Lynnfield based Core i5 750 (no AES-NI) and re-ran the HDD test. The results below were quite promising:

Processor PCMark Vantage HDD % of Unencrypted Performance
Clarkdale - Unencrypted 16713  
Clarkdale - Bitlocker Encryption 13785 82.5%
Lynnfield - Bitlocker Encryption 11744 70.3%


There's a definite benefit to Clarkdale's AES-NI instructions. There's still a performance hit from enabling Bitlocker, but it's not nearly as great as on Lynnfield and other architectures that don't have AES-NI support. With a smaller decrease in I/O performance from enabling full disk encryption, there's also a smaller hit to application performance as well. This is huge for corporate desktops/notebooks.

Most of those machines aren't quad-core encoding monsters; they use dual-core processors. The upgrade from Core 2 seems like it'd be worth it, or at least AES-NI will probably keep AMD out of the running for consideration.

Intel HD Graphics: A Lot Better ASUS Saves the Day: Simulated Core i3s & The Test


View All Comments

  • yuhong - Monday, January 4, 2010 - link

    "The Clarkdale lineup is honestly made up of CPUs that are too expensive. The Core i5 670, 661/660 and 650 are all priced above $170 and aren’t worth the money. The problem is Lynnfield’s turbo mode gives you high enough clock speeds with two threads that there’s no need to consider a dual-core processor. You can buy a Core i5 750, have more cores than any of these Clarkdales and run at close enough to the same frequencies for $196."
    But then you have to pay extra for a discrete graphic card and not every application need the extra graphic power!
  • Paulman - Monday, January 4, 2010 - link

    Wow, I was going to write about how you wouldn't have to buy a discrete graphics card if you went with a Core i5 750 because you could just choose a motherboard with an integrated graphics chip. But then I checked online and it seems that there aren't any P55-based boards with integrated graphics - wow! Wouldn't have believed it myself.

    However, Anand's point still stands when comparing the Clarkdale i5's to the Phenom II X4, for which you can get many boards with integrated graphics.
  • Inkie - Sunday, January 10, 2010 - link

    "when comparing the Clarkdale i5's to the Phenom II X4, for which you can get many boards with integrated graphics"

    ...but Clarkdale already has integrated graphics.
  • ssj4Gogeta - Friday, January 8, 2010 - link

    It's because P55 is a southbridge, not a northbridge. Reply
  • Taft12 - Monday, January 4, 2010 - link

    But then you have to pay extra for a discrete graphic card and not every application need the extra graphic power!

    Only if you don't already have any PCI-E x16 card. Is that true for a single reader of this site? And truly ANY PCI-E card will perform better than Intel's on-chip solution, even one 3 generations old.
  • ereavis - Monday, January 4, 2010 - link

    so the price goes up another $30-$40. As to your question of truth, yes I spend 40 hours a week on an intel IGP dual core as it is, so do the other 1000 people in this building doing engineering work that's processor demanding but graphics independent. Reply
  • nubie - Monday, January 4, 2010 - link

    There are rafts of HP 8400 OEM pci-e cards on ebay right now for $15 (total, no shipping or tax), that should even accelerate your Flash 10.1 and video just fine.

    If you even need it that is, and it is clear that for many there is absolutely no use for more than the integrated graphics.
  • oc3an - Monday, January 4, 2010 - link

    Hi Anand. Looks to me like something weird is up with your Everest benchmarks. Shouldn't the 24X multiplier have the faster scores?

  • Rajinder Gill - Monday, January 4, 2010 - link

    Hi Patrick,

    Fixed it, the images were reversed.


  • maxfisher05 - Monday, January 4, 2010 - link

    Good Article Anand. I'm going to be building my first HTPC soon, but I want to be able to do some light gaming on it, and it doesn't look like the integrated graphics have come far enough yet. If the 661 was priced lower I would consider it, but for nearly the price of a 750 you are right in saying it makes no sense. 750 + 5750 discrete graphics for me please :)

    Will someone be posting an updated system buyers' guide soon?

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