Several responses to a question I asked earlier suggested I try Opera kiosk mode, so I decided to download it and give it a try. Once the download had completed and the disk image was being verified, Safari hung for over a minute and there were periods where Safari used a very high %CPU:

alt text

In Mac OS X 10.5, I was accustomed to seeing Safari freeze, but it never used up more than 200% CPU (2 cores x 100%). Is this a bug in Activity Monitor? Or does this mean that %CPU is now more akin to system load?

  • This looks like a bug. Do you see high numbers when the program is NOT marked "Not Responding"? – nik Sep 7 '09 at 2:37
  • Yeah, this was the only time I saw it. I actually went as high as 3,000% for a second, but the system was barely responsive so it was difficult to get a screenshot. – Kyle Cronin Sep 7 '09 at 4:48
up vote 19 down vote accepted

The % CPU is relative to 1 core, so 726% is using almost 8 cores. Core is loosely defined, so 1 Hyper-Threaded, "virtual" core looks like 2 cores to Activity Monitor.

What type of system do you have? If it is just 2 cores (which is seems to be) then nik's answer sounds correct.

A late model 8-core system can look like 16 cores to Activity Monitor:

alt text

  • 1
    Yeah, it's a 2-year-old MacBook - 1 processor, 2 cores. So... probably a bug. – Kyle Cronin Sep 7 '09 at 4:47
  • 2
    If the CPU is a two core, a 700% CPU usage is a bug :) – Martin Marconcini Jan 24 '11 at 9:48

Your Answer


By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service, privacy policy and cookie policy, and that your continued use of the website is subject to these policies.

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