The internal cpu clock runs at twice the speed of the external clock.
I've worked in the semiconductor industry for 25 years, and can tell you that speed "binning" is done this way:
1) Us engineers devise the worst possible test, at the worst possible conditions (voltage, temperature) for each speed grade.
2) The parts are binned out to stockroom as the fastest grade they will work at.
3) Production control then select ones that meet the minimum speed for orders they have, which could include faster parts, and mark them as such.
If, as is often the case, the natural speed distribution is faster than the market requires, then what is shipped may well work faster than it is branded :-)
Another reason why this may happen is maybe the yield of 40MHz parts was just not high enough to be able to reliably count on the supply of them, so they were just not offered.
If DayStar understood this they could easily buy 33MHz and then test which would run at 40MHz themselves. They then offer those at a premium, the rest going into the 33MHz offering.
Hope that's of interest.
John
PS I remember working at Motorola when the first 68000's came out, and going "wow", when looking at it under a microscope! Time moves one.....
On Friday, April 30, 2004, at 09:53 PM, Mark Benson wrote:
I have a turbo040 card in my Performa 600 that I am trying to build into a Super 68k Nubus machine. It registers in every info tool I've tried in Mac OS as 40MHz, even in the QuadControl 2.2 panel. The CPU is clearly a XC68040HRC33M however - a 33MHz chip. The Oscillator can is 20MHz and I have read up that 20MHz cans on these cards make them run at 40MHz. I highly doubt the oscillator has been changed as the soldering is far too neat and there are no marks that indicate it's ever been removed.
Was Daystar overclocking these chips at the factory?
-- Mark Benson
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