TICK1 measures the resolution of the clock being used in the benchmark measurements, which is the time interval between successive ticks of the clock. A succession of calls to the timer routine are inserted in a loop and executed many times. The differences between successive values given by the timer are then examined. If the changes in the clock value (or ticks) occur less frequently than the time taken to enter and leave the timer routine, then most of these differences will be zero. When a tick takes place, however, a difference equal to the tick value will be recorded, surrounded by many zero differences. This is the case with clocks of poor resolution; for example most UNIX clocks that tick typically every 10 ms. Such poor UNIX clocks can still be used for low-level benchmark measurements if the benchmark is repeated, say, 10,000 times, and the timer calls are made outside this repeat loop.
With some computers, such as the CRAY series, the clock ticks every cycle of the computer, that is to say every 6ns on the Y-MP. The resolution of the CRAY clock is therefore approximately one million times better than a UNIX clock, and that is quite a difference! If TICK1 is used on such a computer the difference between successive values of the timer is a very accurate measure of how long it takes to execute the instructions of the timer routine, and therefore is never zero. TICK1 takes the minimum of all such differences, and all it is possible to say is that the clock tick is less than or equal to this value. Typically this minimum will be several hundreds of clock ticks. With a clock ticking every computer cycle, we can make low-level benchmark measurements without a repeat loop. Such measurements can even be made on a busy timeshared system (where many users are contending for memory access) by taking the minumum time recorded from a sample of, say, 10,000 single execution measurements. In this case, the minimum can usually be said to apply to a case when there was no memory access delay caused by other users.
TICK1 exists and forms part of the Genesis benchmarks [12].