INT 15 - System BIOS Services

For more information see the following topics:

	 INT 15,0  Turn cassette motor on (PC,PCjr only)
	 INT 15,1  Turn cassette motor off (PC,PCjr only)
	 INT 15,2  Read blocks from cassette (PC,PCjr only)
	 INT 15,3  Write blocks to cassette (PC,PCjr only)
	 INT 15,F  PS/2 format periodic interrupt (PS/2 only)
	INT 15,20  PRINT.COM Critical region flag (undocumented DOS 3.x+)
	INT 15,21  PS/2 power on self test (PS/2 except 30)
	INT 15,40  Read / modify profiles (convertible only)
	INT 15,41  Wait on external event (convertible only)
	INT 15,42  Request system power off (convertible only)
	INT 15,43  Read system status (convertible only)
	INT 15,44  (De)activate internal modem power (convertible)
	INT 15,4F  Keyboard intercept  (BIOS date specific)
	INT 15,80  Device open
	INT 15,81  Device close
	INT 15,82  Program termination
	INT 15,83  Event wait
	INT 15,84  Joy-Stick support
	INT 15,85  System request key pressed
	INT 15,86  Elapsed time wait (AT and after)
	INT 15,87  Move block to/from extended memory
	INT 15,88  Extended memory size determination
	INT 15,89  Switch processor to protected mode
	INT 15,90  Device busy
	INT 15,91  Interrupt complete
	INT 15,C0  Return system configuration parameters (PS/2 only)
	INT 15,C1  Return extended BIOS data address (PS/2 only)
	INT 15,C2  Pointing device BIOS interface (PS/2 only)
	INT 15,C3  Enable/Disable watchdog timer
	INT 15,C4  Programmable option select

	- CF is set and AX is left unchanged if a function requested in AH
	  isn't supported
	- some Tandy BIOS's fail to restore interrupts on return from INT 15