Of the Intel Pentium series CPU features that are not accessible from C/C++, one instruction is very interesting to performance-minded programmers. That's the RDTSC (Read Time Stamp Counter) instruction, which returns the number of clock cycles passed since the booting of the CPU in 64-bit unsigned integer, through the EDX and EAX 32-bit general register pair. This means you can time your program in 5-nanosecond precision on a Pentium 200-MHz machine for 117 years.