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  The twelve ROM BIOS interrupts fall into five groups (Figure 8-1):

  .  Six interrupts serve specific peripheral devices.

  .  Two interrupts report on the computer's equipment.

  .  One interrupt works with the time/date clock.

  .  One interrupt performs the print-screen operation.

  .  Two interrupts place the computer into another state altogether,
     activating ROM BASIC and the system start-up routine.

  As you'll see, most of the interrupts are tied to a group of subservices
  that actually do the work. For example, the video service interrupt 10H
  (decimal 16) has 25 subservices that do everything from setting the video
  mode to changing the size of the cursor. You call a subservice by invoking
  its governing interrupt and specifying the subservice number in register
  AH. This process is explained in the example at the end of this chapter.


  Interrupt
  Hex   Dec          Use
  --------------------------------------------------------------------------
  Peripheral Devices Services
  10H   16           Video-display services (see Chapter 9)
  13H   19           Diskette services (see Chapter 10)
  14H   20           Communications services (see Chapter 12)
  15H   21           System services (see Chapter 12)
  16H   22           Standard keyboard services (see Chapter 11)
  17H   23           Printer services (see Chapter 12)

  Equipment Status Services
  11H   17           Equipment-list service (see Chapter 12)
  12H   18           Memory-size service (see Chapter 12)

  Time/Date Service
  1AH   26           Time and date services (see Chapter 12)

  Print-Screen Service
  5H   5             Print-screen service (see Chapter 12)

  Special Services
  18H   24           Activate ROM BASIC (see Chapter 12)
  19H   25           Activate bootstrap start-up routine (see Chapter 12)
  --------------------------------------------------------------------------


  Figure 8-1.  The 12 ROM BIOS services.