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, 2009 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. Sep 7, 2009 at 4:48

1 Answer 1


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. Sep 7, 2009 at 4:47
  • 2
    If the CPU is a two core, a 700% CPU usage is a bug :) Jan 24, 2011 at 9:48

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