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 turn (console, disk, serial port, 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 in 1975 for CP/M, 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 DOS or CP/M in