mcputer.com Has All Your Memory Needs
February 1st, 2009
SYSTEM CLOCK A computer’s system clock resides on the motherboard. It sends out a signal to all other computer components in rhythm, like a metronome. This rhythm is typically drawn as a square wave, like this: In reality, however, the actual clock signal, when viewed with an oscilloscope, looks more like the example shown below. Each wave in this signal measures one clock cycle. If a system clock runs at 100MHz, that means there are 100 million clock cycles in one second. Every action in the computer is timed by these clock cycles, and every action takes a certain number of clock cycles to perform.
When processing a memory request, for instance, the memory controller can report to the processor that the data requested will arrive in six clock cycles. It’s possible for the CPU and other devices to run faster or slower than the system clock. Components of different speeds simply require a multiplication or division factor to synchronize them.
For example, when a 100MHz system clock interacts with a 400MHz CPU, each device understands that every system clock cycle is equal to four clock cycles on the CPU; they use a factor of four to synchronize their actions. Many people assume that the speed of the processor is the speed of the computer. But most of the time, the system bus and other components run at different speeds.
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