I am a bit confused between CPU clock and instruction clock. I brought the following figure from this source as illustration. Does instruction clock imply the time it takes by the cpu clock to execute (possibly by multiple clock cycles as shown in the figure)? If yes, can I always visualize this process using this figure.

enter image description here

up vote 1 down vote accepted

The CPU clock is the frequency at which the oscillations of the silicon happen when electricity is passed through it. The higher the frequency, the faster the clock rate (e.g. 2.4 GHz).

The instruction clock, is the number of CPU clocks the processor will take to fetch the relevant instructions from memory, decode them, and then execute them.

Based on the image you've posted, that clock has a 2:1 ratio, that is, for every 2 CPU clocks, 1 instruction will be executed. Another way of saying it is that the instruction execution will delay 2 clock ticks.

Does instruction clock imply the time it takes by the cpu clock to execute?

Basically, yes.

If yes, can I always visualize this process using this figure.

From a high level, yes, but just remember not all processors (even of the same manufacturer) are created equally, and with advancements like multiple instruction pipelines in modern processors, things can get tricky quickly.

Hope that can help clear some confusion.

  • PERFECT explanation .. Thank you for your effort and sharing the knowledge – Mike Feb 19 '16 at 2:27
  • @Mike, glad I could help :) – txtechhelp Feb 19 '16 at 2:27

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