IBMBIO.COM
Encyclopedia
IBMBIO.COM is the filename of the DOS-BIOS
in many DOS
operating systems, and as such part of PC-DOS
, earlier versions of MS-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:
Under DR-DOS, the first step is skipped, since a DR-DOS boot sector mounts the FAT filesystem, locates the IBMBIO.COM (or DRBIOS.SYS) file in the root directory and loads it into memory by itself. It is not necessary for the IBMBIO.COM file to reside at a fixed physical position or be stored in consecutive sectors. Instead, it can be simply copied to the disk (without SYS), given a DR-DOS boot sector already resides on the disk.
BIOS
In IBM PC compatible computers, the basic input/output system , also known as the System BIOS or ROM BIOS , is a de facto standard defining a firmware interface....
in many DOS
DOS
DOS, short for "Disk Operating System", is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.Related...
operating systems, and as such part of PC-DOS
PC-DOS
IBM PC DOS is a DOS system for the IBM Personal Computer and compatibles, manufactured and sold by IBM from the 1980s to the 2000s....
, earlier versions of MS-DOS, and DR DOS 5.0 and higher (with the exception of DR-DOS 7.06). It serves the same purpose as IO.SYS
IO.SYS
IO.SYS is an essential part of MS-DOS and Windows 9x. It contains the default MS-DOS device drivers and the DOS initialization program.- Boot sequence :...
in MS-DOS
MS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
, 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
Personal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
bootup sequence, the first sector of the boot disk is loaded into memory and executed. If this is the DOS boot sector
Boot sector
A boot sector or boot block is a region of a hard disk, floppy disk, optical disc, or other data storage device that contains machine code to be loaded into random-access memory by a computer system's built-in firmware...
, 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.COMIBMDOS.COMIBMDOS.COM is the filename of the DOS kernel. It exists in DR-DOS and PC-DOS systems, with MS-DOS using MSDOS.SYS. The file is located in the root directory of the drive containing the operating system....
. - Initializes each default device driverDevice driverIn computing, a device driver or software driver is a computer program allowing higher-level computer programs to interact with a hardware device....
in turn (console, disk, serial portSerial portIn computing, a serial port is a serial communication physical interface through which information transfers in or out one bit at a time...
, et cetera). At this point, the default devices are available. - Calls the DOS kernel's initialization routine.
Under DR-DOS, the first step is skipped, since a DR-DOS boot sector mounts the FAT filesystem, locates the IBMBIO.COM (or DRBIOS.SYS) file in the root directory and loads it into memory by itself. It is not necessary for the IBMBIO.COM file to reside at a fixed physical position or be stored in consecutive sectors. Instead, it can be simply copied to the disk (without SYS), given a DR-DOS boot sector already resides on the disk.