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Michael <macallan18@earthlink.net> writes:

> So far this in only known to work on my iBook. It may or may not work on
> different hardware.

It seems to have no effect on my iBook G4 of 1 GHz.  This is the
output from "sysctl -w machdep.cpu_speed=0 && flops && sysctl -w
machdep.cpu_speed=1 && flops":


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Content-Disposition: attachment; filename=cpuspeed.out

machdep.cpu_speed: 1 -> 0

   FLOPS C Program (Double Precision), V2.0 18 Dec 1992

   Module     Error        RunTime      MFLOPS
                            (usec)
     1     -7.6739e-13      0.1109    126.2439
     2     -5.7021e-13      0.0826     84.7114
     3     -2.4314e-14      0.0827    205.4382
     4      6.8612e-14      0.1298    115.5735
     5     -1.6209e-14      0.2049    141.5665
     6      1.3961e-13      0.1393    208.2527
     7     -3.6152e-11      0.2913     41.1946
     8      8.9373e-15      0.1486    201.8356

   Iterations      =  256000000
   NullTime (usec) =     0.0038
   MFLOPS(1)       =   104.8562
   MFLOPS(2)       =    82.9359
   MFLOPS(3)       =   131.8314
   MFLOPS(4)       =   181.8446

machdep.cpu_speed: 0 -> 1

   FLOPS C Program (Double Precision), V2.0 18 Dec 1992

   Module     Error        RunTime      MFLOPS
                            (usec)
     1     -7.6739e-13      0.1113    125.7588
     2     -5.7021e-13      0.0828     84.5561
     3     -2.4314e-14      0.0828    205.4158
     4      6.8612e-14      0.1297    115.6902
     5     -1.6209e-14      0.2051    141.4000
     6      1.3961e-13      0.1393    208.2301
     7     -3.6152e-11      0.2914     41.1872
     8      8.9373e-15      0.1485    202.0333

   Iterations      =  256000000
   NullTime (usec) =     0.0038
   MFLOPS(1)       =   104.6941
   MFLOPS(2)       =    82.9011
   MFLOPS(3)       =   131.7757
   MFLOPS(4)       =   181.9363


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I.e. virtually no difference.  dmesg says among other things:

cpu0 at mainbus0: 7447A (Revision 1.1), ID 0 (primary)
cpu0: HID0 8450c0bc<EMCP,EICE,NAP,DPM,ICE,DCE,SGE,BTIC,FBIOB,ABE,BHT>
cpu0: 534.98 MHz, 512KB L2 cache
[...]
enabling Intrepid CPU speed control
CPU speed is low

envstat says that the voltage changes between 1.432 and 1.680 volts,
though.

Magnus

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