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BIOS interrupt calls perform hardware control or I/O functions requested by a program, return system information to the program, or do both. A key element of the purpose of BIOS calls is abstraction - the BIOS calls perform generally defined functions, and the specific details of how those functions are executed on the particular hardware of the system are encapsulated in the BIOS and hidden ...
Prior to the development and ubiquitous adoption of the Plug and Play BIOS standard, an add-on device such as a hard disk controller or a network adapter card (NIC) was generally required to include an option ROM in order to be bootable, as the motherboard BIOS did not include any support for the device and so could not incorporate it into the BIOS's boot protocol.
Likewise, the IO.SYS of the older system is named IO.DOS for as long as Windows 9x is active. DR-DOS 7.06 (only this version) also follows this scheme and the IO.SYS filename in order to become bootable via MS-DOS boot sectors. Similarly, FreeDOS uses a combined system file as well, but names it KERNEL.SYS.
This is why the motherboard BIOS ROM is in segment F000 in the conventional memory map. During the POST flow of a contemporary BIOS, one of the first things a BIOS should do is determine the reason it is executing. For a cold boot, for example, it may need to execute all of its functionality.
In computing, the BIOS parameter block, often shortened to BPB, is a data structure in the volume boot record (VBR) describing the physical layout of a data storage volume. On partitioned devices, such as hard disks , the BPB describes the volume partition, whereas, on unpartitioned devices, such as floppy disks , it describes the entire medium.
Ralf Brown's Interrupt List (aka RBIL, x86 Interrupt List, MS-DOS Interrupt List or INTER) is a comprehensive list of interrupts, calls, hooks, interfaces, data structures, CMOS settings, memory and port addresses, as well as processor opcodes for x86 machines from the 1981 IBM PC up to 2000 (including many clones), [1] [2] [nb 1] most of it still applying to IBM PC compatibles today.
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.
The program was also distributed with many language compilers for MS-DOS in the 1980s, and included with certain versions of IBM PC DOS. PhysTechSoft & Paragon Technology Systems PTS-DOS, [7] Digital Research DR DOS 6.0, [8] and Datalight ROM-DOS, [9] also include an implementation of the exe2bin command. The command is also available in FreeDOS.