Rtlinux achieves an accurate and efficient timing, using a programmable interval timer to interrupt the CPU only when needed. The Intel 8354 timer chip present in some form in all IBM PC compatible computers is set into the interrupt-on-terminal-count mode. Using this mode, an interrupt can be scheduled with approximately 1 microsecond precision. In this scheme the overhead of interrupt processing is minimal while the timer resolution is high. However, reprogramming the 8354 timer on PCs takes a long time because the timer is not on the processor chip. Fortunately, most modern CPUs, e. g., Pentiums [ref], have timers on-chip in addition to the 8354.