I have a 5k iMac (Late 2015), with a spinning hard disc, running El Capitan.

I'm considering enabling FileVault, but I'm concerned if it will hurt responsiveness. Will it? I understand that it doesn't on a SSD, but this machine has a spinning hard disc.

2 Answers 2


Once the initial encryption has finished you are very unlikely to notice any difference in day-to-day usage.

Your iMac's CPU also contains specific features that assist with encryption (AES).


It should be fine as any bottleneck would be the CPU power involved in encrypting/decrypting the data as it is being accessed.

The slower drive would actually require less CPU power than an SSD.

  • Interesting. Not to disagree, but SSDs are so responsive that latency has to increase hugely for it to be noticeable, while HDDs have high latency to begin with, so even a small increase may be detrimental. Jul 29, 2016 at 15:39

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