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  Clocks and timers are the heartbeat of a computer. The computer's
  essential functions of computation and data transfer take place in step
  with the pulses generated by electronic clocks. PCs and PS/2s play host to
  several clocks and timers that you should know about:

  .  The system timer generates "clock-ticks" and other timing pulses at
     precisely controlled intervals.

  .  The sound generator produces tones through a speaker with a wide range
     of frequencies and durations.

  .  The real-time clock/calendar keeps track of the date and time and can
     also serve as an "alarm clock." (This is supported only in the PC/AT
     and PS/2s.)

  To understand how to use the system timer, the sound generator, and the
  real-time clock, you need to know about the basic clock and timing
  mechanisms in PCs and PS/2s. That is what we'll outline in this chapter.