IBMBIO.COM
IBMBIO.COM is the filename of the system initialization code and builtin device drivers in many DOS operating systems, and as such part of PC DOS and DR DOS 5.0 and higher (with the exception of DR-DOS 7.06). It serves the same purpose as IO.SYS in MS-DOS, or DRBIOS.SYS in DR DOS 3.31 to 3.41.
The filename is referred to in the boot sector by the boot loader.
In the PC bootup sequence, the first sector of the boot disk is loaded into memory and executed. If this is the DOS boot sector, it loads the first three sectors of IBMBIO.COM into memory and transfers control to it. IBMBIO.COM then:
Loads the rest of itself into memory. For this to work, IBMBIO.COM and its directory entry must be located at fixed physical positions on the disk and stored in consecutive sectors, conditions of which the SYS utility must take care of.
Loads the DOS kernel. The kernel is stored in IBMDOS.COM.
Initializes each default device driver in turn (console, disk, serial port, et cetera). At this point, the default devices are available.
