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PowerBook G4 12" (and possibly other models) reporting 533 Mhz clock frequency

PowerBook G4 12" (and possibly other models) reporting 533 Mhz clock frequency

We've confirmed a behavior in-house where the PowerBook G4 12" (867 Mhz) and possibly other models report a 533 MHz clock frequency in the terminal.

MacFixIt reader Eric Woehler, who is experiencing the same issue, writes:

"I have a 12 inch PowerBook G4 with 640Mb of RAM, running 10.3.3. Machine is about 9 months old.

"Typing the command
  • sysctl hw.cpufrequency

"in Terminal would show the CPU frequency. On my machine it showed

  • hw.cpufrequency: 533333332
  • [Ed.- corresponding to a 533 MHz clock rate]

"to reset the CPU back to top speed required a reset of the Power Management Unit (PMU) and a reboot. Now I get

  • hw.cpufrequency: 866666664

"with a very noticeable jump in performance - start up time, app loading, file opening etc - it is a real performance jump. The problem is next time I restart (e.g. after system software upgrade etc), the CPU is reset to 533 MHz. Less than useful."

As in Eric's case, resetting the PMU on our in-house PowerBook G4 12" restored the normal 867 MHz clock speed. And, as in Eric's case, our in-house system reverted to the slower 533 MHz frequency after a routine restart.

Interestingly, Apple System Profiler shows an 867 MHz frequency in both cases. It should also be noted that "Optimize Energy Settings" was set to "Highest Performance" in the Energy Saver pane of System Preferences.

Resetting the PMU on a PowerBook G4 12" can be accomplished by the following process:

  1. Shut down the PowerBook.
  2. Press the Shift, Option, Control, and Power keys simultaneously
  3. Wait 5 seconds
  4. Start the PowerBook via the power key

Aside from being inconvenient, resetting the PMU after each restart is also not recommended by Apple. As explained in Knowledge Base article #58416 "A reset button is not intended for resolution of a stall or situation in which the computer is non-responsive. A reset should not be necessary except as a last resort in cases where a hardware failure of the power management system is suspected. Pressing the reset button resets the PowerBook hardware, including NVRAM, and forces the computer to shut down. [...] only reset the computer if nothing else has resolved the situation."

A post on the Apple Discussion boards, however, explains that in some cases, this may be a purely cosmetic bug. Poster Matt Peacock writes:

"The 533MHz value is a value stored in energy configuration files on the machine, which were updated in 10.2.8 , and "sysctl hw.cpufrequency" (that command shows just the CPU frequency rather than everything) reports the setting in this file, not the actual CPU speed. The setting refers to the "reduced" mode of the CPU.

"XBench also uses this file, which is why earlier versions reported the CPU speed incorrectly after the 10.2.8 update. An easy way to prove this is to run XBench and compare your scores to the scores on the web site, you'll see they are in-line. Crucially however, they are almost identical to the scores prior to the 10.2.8 update (when the Terminal correctly reported CPU speed). Then, if you set your CPU setting to "reduced", you'll get a score of relative to a 333MHz drop, or, 533MHz as the configuration file specifies. XBench has since been updated to use the correct value, but apparently the Terminal hasn't."

If your PowerBook is reporting a lower clock speed in the Terminal, please let us know if you are experiencing slower real-world performance, or have success gaining performance with a PMU reset.

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