IBMBIO.COM is a

system file A system file in computers is a critical computer file without which a computer system may not operate correctly. These files may come as part of the operating system, a third-party device driver or other sources. Microsoft Windows and MS-DOS mark ...

in many

DOS DOS (, ) is a family of disk-based operating systems for IBM PC compatible computers. The DOS family primarily consists of IBM PC DOS and a rebranded version, Microsoft's MS-DOS, both of which were introduced in 1981. Later compatible syste ...

operating systems. It contains the system initialization code and all built-in device drivers. It also loads the DOS kernel ( IBMDOS.COM) and optional pre-loadable system components (like for

disk compression A disk compression software utility increases the amount of information that can be stored on a hard disk drive of given size. Unlike a file compression utility, which compresses only specified files—and which requires the user to designate ...

or security), displays boot menus, processes configuration files (like CONFIG.SYS) and launches the shell (like COMMAND.COM). The file is part of

IBM International Business Machines Corporation (using the trademark IBM), nicknamed Big Blue, is an American Multinational corporation, multinational technology company headquartered in Armonk, New York, and present in over 175 countries. It is ...

's PC DOS (all versions) as well as of DR DOS 5.0 and higher (with the exception of DR-DOS 7.06). It serves the same purpose as the file IO.SYS in

MS-DOS MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few op ...

, or DRBIOS.SYS in DR DOS 3.31 to 3.41. (For compatibility purposes with some DOS applications the IBMBIO.COM file name was briefly also used by the IBM version of OS/2 1.0, where it resembled the OS2BIO.COM file as used by

Microsoft Microsoft Corporation is an American multinational corporation and technology company, technology conglomerate headquartered in Redmond, Washington. Founded in 1975, the company became influential in the History of personal computers#The ear ...

.) The file is located in the

root directory In a Computing, computer file system, and primarily used in the Unix and Unix-like operating systems, the root directory is the first or top-most Directory (computing), directory in a hierarchy. It can be likened to the trunk of a Tree (data st ...

of the bootable

FAT In nutrition science, nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such chemical compound, compounds, most commonly those that occur in living beings or in food. The term often refers specif ...

-formatted drive/partition (typically C:\) and typically has the ''system'', ''hidden'', and (since DOS 2.0 also the) ''read-only''

file attribute File attributes are a type of metadata that describe and may modify how files and/or directories in a filesystem behave. Typical file attributes may, for example, indicate or specify whether a file is visible, modifiable, compressed, or encrypte ...

s set. Under DR-DOS the file may be optionally password-protected as well. Under PC DOS, the ''system'' attribute is set in order to mark the file as non-movable, a restriction technically not necessary under DR-DOS. As IBMBIO.COM is a binary image containing executable code rather than a true COM-style program, the ''hidden'' attribute is set to keep the file from being accidentally invoked at the command prompt, which would lead to a crash. This is no longer necessary for DR-DOS 7.02 and higher, because under these systems the file is a

fat binary A fat binary (or multiarchitecture binary) is a computer executable program or library which has been expanded (or "fattened") with code native to multiple instruction sets which can consequently be run on multiple processor types. This results ...

also containing a tiny COM-style stub just displaying some version info and exiting gracefully when not being loaded by a

boot sector A boot sector is the disk sector, sector of a persistent data storage device (e.g., hard disk, floppy disk, optical disc, etc.) which contains machine code to be loaded into random-access memory (RAM) and then executed by a computer system's bui ...

. In the PC bootup sequence, the first sector of the boot volume contains a

boot loader A bootloader, also spelled as boot loader or called bootstrap loader, is a computer program that is responsible for booting a computer and booting an operating system. If it also provides an interactive menu with multiple boot choices then it's o ...

called the volume boot record (VBR) and is loaded into memory and executed. If this is a VBR of PC DOS before 3.3 it would load both system files into memory by itself. As the PC DOS VBR cannot mount the FAT file system, the system files have to be stored in the first directory entries on the disk and be located at fixed physical positions on the disk stored in consecutive sectors, conditions of which the SYS utility must take care of. If the loaded boot sector is a PC DOS 3.3 (or newer) VBR, the requirements are slightly relaxed. The system files still have to be stored in the first two root directory entries on the disk, but the VBR will use only the first entry to load the first three sectors of IBMBIO.COM into memory and transfer control to it. This part of IBMBIO.COM then contains a somewhat larger boot loader which: #Loads the rest of itself into memory. Before PC DOS 5.0 the system files still had to be stored at fixed physical positions on the disk and stored in consecutive sectors. With PC DOS 5.0 (and higher) this requirement was reduced down to the first three sectors of IBMBIO.COM only. #Loads the DOS kernel. The kernel is stored in IBMDOS.COM. #Initializes each default

device driver In the context of an operating system, a device driver is a computer program that operates or controls a particular type of device that is attached to a computer or automaton. A driver provides a software interface to hardware devices, enabli ...

in turn (

console Console may refer to: Computing and video games * System console, a physical device to operate a computer ** Virtual console, a user interface for multiple computer consoles on one device ** Command-line interface, a method of interacting with ...

, disk,

serial port A serial port is a serial communication Interface (computing), interface through which information transfers in or out sequentially one bit at a time. This is in contrast to a parallel port, which communicates multiple bits simultaneously in Pa ...

, et cetera). At this point, the default devices are available. #Calls the DOS kernel's initialization routine. Under DR DOS 5.0 and higher, the first step is skipped, since a DR-DOS VBR is capable of mounting the FAT file system, locate the IBMBIO.COM (or DRBIOS.SYS) file anywhere in the root directory and load it into memory by itself. The filename of the IBMBIO.COM file to be loaded by the boot sector is stored in the boot sector rather than necessarily in the first root directory entry, likewise the filename of the IBMDOS.COM file to be loaded by IBMBIO.COM is stored in IBMBIO.COM itself rather than necessarily in the second directory entry on the disk. Also, similar to the IBMBIO.COM loader in the VBR, the IBMDOS.COM loader in IBMBIO.COM is capable of rudimentarily mounting the filesystem as well, therefore it is not necessary for the system files to be stored in the first two directory entries, to reside at fixed physical positions or be stored in consecutive sectors. Consequently, it is also no longer necessary to set the ''system'' attribute. Instead, the system files can be simply copied to the disk (without SYS), given a DR-DOS boot sector already resides on the disk. Microsoft sometimes calls this component the I/O system, but it is generally known as DOS BIOS (the DOS-related part of the Basic Input/Output System). The term BIOS was originally coined by

Gary Kildall Gary Arlen Kildall (; May 19, 1942 – July 11, 1994) was an American computer scientist and microcomputer entrepreneur. During the 1970s, Kildall created the CP/M operating system among other operating systems and programming tools, and s ...

in 1975 for

CP/M CP/M, originally standing for Control Program/Monitor and later Control Program for Microcomputers, is a mass-market operating system created in 1974 for Intel 8080/Intel 8085, 85-based microcomputers by Gary Kildall of Digital Research, Dig ...

, but is also used to describe a similar component or layer in other operating systems by Digital Research, IBM, Microsoft and many others. In a more generic sense, some vendors refer to this portion as the RAM BIOS of operating systems such as

in order to contrast it with the built-in ROM BIOS of a machine.

Notes

References

{{Disk operating systems DOS files

See also

Notes

References