IBMBIO.COM is a system file in many DOS 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 or security), displays boot menus, processes configuration files (like CONFIG.SYS) and launches the shell (like COMMAND.COM). The file is part of IBM'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, 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.) The file is located in the root directory of the bootable FAT-formatted drive/partition (typically C:\) and typically has the system, hidden, and (since DOS 2.0 also the) read-only file attributes 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 also containing a tiny COM-style stub just displaying some version info and exiting gracefully when not being loaded by a boot sector. In the PC bootup sequence, the first sector of the boot volume contains a boot loader 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