= Clock frequency
{title2=$f=1/T_c$}
<Clock frequency> is the number of cycles of a <clock signal> per unit time. If its period is $T_c$, its <frequency> is $f=1/T_c$. A $3\times10^9$ <hertz> clock has a nominal period of about $0.333\times10^{-9}$ <seconds>. The clock coordinates timed operations; it does not specify how many complete program <machine instructions>[instructions] are performed in each cycle.
For a fixed-frequency processor, execution time can be written as <machine instruction>[instruction] count times average <cycles per instruction> divided by <frequency>. Raising <frequency> can improve that component of runtime, but it may also require a different pipeline organization or increase power and thermal constraints. Memory waits and dependencies can leave some cycles without completed <machine instructions>[instructions], while <superscalar execution> can complete several <machine instructions>[instructions] in one cycle. Performance comparisons must therefore include the workload and <microarchitecture>, not only the clock rating.
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