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Difference between revisions of "Squidlet IC"
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Latest revision as of 23:47, 19 March 2023
The Squidlet chip synchronizes the operations of the different clocks used within Power Macs to control the CPU and subsystems on the logic board.
All computers require at least two clocks: The system clock and the CPU bus clock. The system clock controls the rate of execution of instructions with the CPU itself, and the CPU bus clock controls the rate of data transfer across the system bus.
The system clock on all Power Macs is a CMOS chip powered by a removable/replaceable lithium battery. As you might already realize, though, the system clock is set differently on 6100, 7100, and 8100 systems, which all use different-speed CPUs.
For 6100/60 systems, the system clock runs (fires pulses) at a frequency of 60 MHz (60 million cycles, or pulses, per second); for 7100/66 systems, the system clock runs at 66 MHz, and for 8100/80 systems, the system clock runs at 80 MHz (keep in mind that all three systems are available with faster chips).
The CPU bus clock on Power Macs runs at half the frequency of the system clock. So, the CPU bus clock on the 6100/60 systems runs at 30 MHz, the bus clock on the 7100/66 systems runs at 33 MHz, and the bus clock on the 8100/80 systems runs at 40 MHz.