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Re: 68040 clock doubling



John de Bruin (j.bruin@auckland.ac.nz) wrote:
: Why is this different from clock doubling as in the 486DX/2 CPU?
: And the BCLK is used for all bus timing, whereas the PCLK is used for 
: internal processor logic timing.
: Now as far as I can tell the only difference between this and the DX/2, 
: is that the DX/2 only has one clock and uses a clock 2x multiplier to 
: derive the internal processor speed. Why do the two clocks on the '040 
: _not_ have the same effect as clock doubling?

On a 486, the machine commands are executed with (internally generated)
PCLK, on the 68040 only very few parts of the processor (eg some parts
of the arithmetic unit) are using PCLK, the rest is running at BCLK.

So, the 040 doesn't use the higher clock as much as the 486 does.
This has nothing to do with efficiency, btw.

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