Editing BIOS (section)

== History ==
{{rquote|right|
<pre>/* C P / M   B A S I C   I / O    S Y S T E M (B I O S)
                    COPYRIGHT (C) GARY A. KILDALL
                             JUNE, 1975 */
[…]
/*  B A S I C   D I S K    O P E R A T I N G   S Y S T E M (B D O S)
                    COPYRIGHT (C) GARY A. KILDALL
                            JUNE, 1975 */</pre>
<!-- some whitespace removed from original citation -->
| An excerpt from the BDOS.PLM file header in the [[PL/M]] source code of CP/M 1.1 or 1.2 for [[Lawrence Livermore Laboratories]] (LLL)<ref name="Kildall_1975_BDOS"/>
}}

The term BIOS (Basic Input/Output System) was created by [[Gary Kildall]]<ref name="Swaine_1997_Entrepreneurship" /><ref name="IEEE_2014_BIOS"/> and first appeared in the [[CP/M]] operating system in 1975,<ref name="Kildall_1975_BDOS" /><ref name="Kildall_1980_CPM" /><ref name="IEEE_2014_BIOS"/><ref name="Shustek_2016"/><ref name="Fischer_2001_Ewing" /><ref name="Fraley_2007_Killian" /> describing the machine-specific part of CP/M loaded during boot time that interfaces directly with the [[computer hardware|hardware]].<ref name="Kildall_1980_CPM" /> (A CP/M machine usually has only a simple [[boot loader]] in its ROM.)

Versions of [[MS-DOS]], [[PC DOS]] or [[DR-DOS]] contain a file called variously "[[IO.SYS]]", "[[IBMBIO.COM]]", "IBMBIO.SYS", or "DRBIOS.SYS"; this file is known as the "DOS BIOS" (also known as the "DOS I/O System") and contains the lower-level hardware-specific part of the operating system. Together with the underlying hardware-specific but operating system-independent "System BIOS", which resides in [[Read-only memory|ROM]], it represents the analogue to the "[[CP/M BIOS]]".

The BIOS originally [[Proprietary software|proprietary]] to the [[IBM Personal Computer|IBM PC]] has been [[reverse engineer]]ed by some companies (such as [[Phoenix Technologies]]) looking to create compatible systems.

With the introduction of PS/2 machines, IBM divided the System BIOS into real- and protected-mode portions. The real-mode portion was meant to provide backward compatibility with existing operating systems such as DOS, and therefore was named "CBIOS" (for "Compatibility BIOS"), whereas the "ABIOS" (for "Advanced BIOS") provided new interfaces specifically suited for multitasking operating systems such as [[OS/2]].<ref>{{cite journal |title=The IBM PC BIOS |journal=Byte |year=1989 |last=Glass |first=Brett |pages=303–310 |url=https://archive.org/details/eu_BYTE-1989-04_OCR/page/n373/mode/2up?view=theater |accessdate=2021-12-31 }}</ref>