I force myself to learn a little, and I'm going to try to share some of that here, but any real hardware types will undoubtedly find this pretty basic. The CPU is, of course, the heart of our systems. 66MHz or 266MHz. There is one CPU on this system. Let's start with the simple stuff.
Different processors take different number of clock cycles for different instructions.
The '386 did it in 2 clocks, but a Pentium can do that in one clock cycle. Likewise, a Pentium II is faster than a plain Pentium at the same clock rate. When dealing with a Pentium CPU that existed at the time this code was written, it is giving a reasonably accurate benchmark. It's just how fast it got through a certain loop that contained certain instructions where the time required is known for specific CPU families. When the code does NOT know the family it just guesses.