0

"If one backs up a few hundred gigabytes for an initial encrypted Time Machine snapshot, a particular instruction available on Intel i7 chips enables encrypting on the CPU. The Intel i5 chips, which lack that instruction, require running the encryption in software. The result is that an i7 will run much cooler and take far less time."

My reading of a past generation i5/i7 specs made me conclude the statement above. Is this conclusion accurate?

I'm mainly interested in the answer for macOS, if that matters. Update: The scenario is the following. Say you're out shopping for a Mac. You know you'll encrypt both the internal disk (the boot disk) using FileVault as well as the Time Machine disk(s) using ... and here I'm not clear. Doesn't Time Machine encryption also use FileVault under the hood? In any case, would you select an i7 over an i5, to keep the CPU load (reading/writing from disk and from TM disk) low?

2
  • 1
    My reading of a past generation i5/i7 specs made me conclude the statement above. - What exactly in their specs made you come to that conclusion? E.g. what's that particular instruction available on Intel i7 chips you speak about?
    – flolilo
    Oct 24 '17 at 18:24
  • 1
    @flolilolilo I assume he's talking about the AES-NI instructions. Oct 25 '17 at 0:33
0

If you are talking about the AES instructions being available for accelerating encryption then they have, in a mixed way, been available for many processors across generations and were not specifically limited to i7 processors.

You'd be more correct to say that i3, Pentium and Celeron processors would have had to do the work "the hard way".

From Wikipedia (exceptions, i.e. Lacking AES, bolded)

The following processors support the AES-NI instruction set:[4]

  • Intel[5]
    • Westmere based processors, specifically:
    • Westmere-EP (Xeon 56xx) (a.k.a. Gulftown Xeon 5600-series DP server model) processors.
    • Clarkdale processors (except Core i3, Pentium and Celeron).
    • Arrandale processors (except Celeron, Pentium, Core i3, Core i5-4XXM).
    • Sandy Bridge processors:
      Desktop: all except Pentium, Celeron, Core i3.
      Mobile: all Core i7 and Core i5. Several vendors have shipped BIOS configurations with the extension disabled; a BIOS update is required to enable them.
    • Ivy Bridge processors.
      All i5, i7, Xeon and i3-2115C[10] only.
    • Haswell processors (all except i3-4000m,[11] Pentium and Celeron).
    • Broadwell processors (all except Pentium and Celeron).
    • Silvermont/Airmont processors (all except Bay Trail-D and Bay Trail-M).
    • Skylake processors.
    • Kaby Lake processors.
  • AMD
    • Bulldozer processors.
    • Piledriver processors.
    • Steamroller processors.
    • Excavator processors.
    • Jaguar processors.
    • Puma processors.
    • Zen processors.
0

First of all, we're assuming that yourself and the source both understand we're discussing encryption as opposed to simple compression algorithms. Time Machine has a built-in option to "encrypt backup disk" however you may also encrypt a partition with other tools, BitLocker To Go has been bundled with windows since 8.1 and FileVault with Mac OS X Panther (10.3).

The method and encryption settings (such as Algorithm and KeySize) are unspecified in this question which will affect any answer. The AES algorithm (assumed in other answer) is common but others exist like RSA which is also very ubiquitous (maybe safer but less efficient), a greater KeySize is always better but requires more processing. These parameters will affect how your CPU handles the process.

If you're concerned about overheating your CPU then we may need more info to really help. Each CPU has a thermal design power/point (TDP), as long as you haven't overclocked anything you shouldn't need to worry too much about temperature. You may notice your fan kick in, for significant processing tasks that's likely to happen whether you're using hardware or software for encryption and/or compression.

3
  • I guess I wasn't clear on the scenario: Say you're out shopping for a Mac. You know you'll encrypt both the internal disk (the boot disk) using FileVault as well as the Time Machine disk(s) using ... and here I'm not clear. Doesn't Time Machine encryption also use FileVault under the hood? In any case, would you select an i7 over an i5, to keep the CPU load (reading/writing from disk and from TM disk) low?
    – Calaf
    Oct 25 '17 at 2:16
  • TimeMachine = Backup, FileVault = Encryption "Doesn't Time Machine encryption also use FileVault under the hood?" - No, the partition may be encrypted separately, FileVault is used by OSX to encrypt your home directory. if you're worried about price then get the i5, if you're worried about speed then consider what is the weakest link: for example are you using SSD, is it using ESATA or USB3, etc. Your CPU is only one of many factors, so you probably won't notice the difference between an i5 and an i7.
    – Jason K.
    Nov 1 '17 at 4:11
  • "Time Machine’s encryption and FileVault both use the same underlying drive management technology called CoreStorage. " credit Topher Kessler here: macissues.com/2014/11/07/…
    – Jason K.
    Nov 1 '17 at 4:19
0

Without documentation from Intel and/or testing, its impossible to say.

If a processor supports an instruction/operation another does not. that doesnt mean it will be cooler. Perhaps the extra instruction allows the encryption to run much faster; thereby running the CPU much hotter.

Also, you are comparing apples to oranges. The CPUs are completely different models. One might be designed completely differently, and therefore with a different temperature efficiency.

Again, it really is impossible to say without testing.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.