What is the speed of a PC?

Answer 1

The speed of a PC generally refers to the system clock rate, measured in gigahertz and sometimes megahertz. A megahertz is one million cycles per second, while a gigahertz is a billion cycles per second.

However, that is not the only measure of throughput, and the clock rate can be misleading. So clock rate is not the same thing as performance. Sometimes a machine with a slower clock rate actually runs applications faster than one with a faster clock rate. That was how it was between Intel and AMD for years. The AMD processors could work faster than ones from Intel with a higher clock rate. The difference here has to do with instruction speed. If a machine is of a lower clock rate than another, but its instructions are more efficient and take less clock cycles to complete, then it will likely perform better.

Instruction speed is based on whether the instructions have their own dedicated processing hardware, or if there is microcode to derive them from other instructions. For instance, NEC V20 processor, a replacement for the Intel 8088, performed faster than an 8088 at the same clock rate. The main difference was that it actually had a hard-coded multiplier. The 8088 didn't, but relied on the adder and microcode to loop it to emulate multiplication. The reason the V20 could add circuitry to do multiplication was because they used a newer technology that allowed them to cram more stuff into an IC. So their multiplication instruction was much more efficient since they had the room to add dedicated circuits.