How many instructions per second?

Speed of a computer’s CPU Typically measured in Mhz, Ghz, etc. What does that measure? –Rate of the basic oscillator –not the “time” clock Cycles/sec -> tics/sec –10 Hz -> 10 tics/sec -> 1/10 sec/tic –1 M(ega)hz -> 10 6 tics/sec-> 1 microsec/tic –10 Mhz ->10 7 tics/sec-> 1/10 microsec/tic

What happens in a cycle? Everything is synchronized from that “clock” Moving data across the external bus Moving data across the internal CPU bus Accessing memory Timing microcode steps in a machine language instruction (a fraction of a single machine language instruction) MULTIPLE tics for an activity to complete

How many cycles/sec for an instruction? Varies greatly. Instructions which only affect internal registers are quick –logical ops like and/or/register swaps Numerical calcs (floating point is worse than integers, multiply is worse than add), string ops(if available) are much longer. Varies from a few cycles to 100s of cycles.

Example Assume cpu is 1 GHz. Assume average instruction take 10 cycles. How many instructions/sec? 1 GHz -> 1 x secs per tic or 1 nanosecond Average instruction takes 10 cycles -> 10 nanoseconds