int intdosx( union REGS *inregs, union REGS *outregs,
			struct SREGS *segregs )


	- prototype in dos.h

	- executes 8086 software interrupt INT 21
	- copies register values from inregs into the registers
	- copies segregs->x.ds and segregs->y.es into DS/ES
	- if CF is set, an error has occurred
	- unique to DOS
	- see	intdos()  int86()  int86x()  intr()  REGS