Quincy Center for Technical Education
Computer Technology Department

Power On Self Test

  1. CPU Register reset to F000
  2. This Counter reset is the address of the of the BOOT program stored in ROM chips that contain the Basic Input/Output System (BIOS)
  3. This invokes a series of system checks known as the POST
  4. The system sends signals over the system BUS -checks to see if they are all functioning.
  5. POST runs a series of test on the RAM chips (counting bytes)
  6. The CPU checks to make sure a keyboard is connected and if any keys have been pressed.
  7. POST sends signals to other paths on the BUS to any drives.
  8. These signals are checked against the CMOS (battery keeps CMOS from forgetting) setup data.
  9. Some expansion boards have their own BIOS, in that case that code is recognized (VIDEO or Disk controllers) Returns a single beep if system is OK. See error codes.
  10. Now the system is loaded. IO.SYS first.
  11. CONFIG.SYS is loaded (device drivers)
  12. MSDOS.SYS is then loaded.
  13. COMMAND .COM is loaded (the command interpreter)
  14. AUTOEXEC.BAT is then run (other devices and programs TSRs)