* The 400 / 800's 10 KB operating system was replaced with a simpler 2 KB BIOS, of which 1 KB is the built-in character set.

Advanced power management ( APM ) is an API developed by Intel and Microsoft and released in 1992 which enables an operating system running an IBM-compatible personal computer to work with the BIOS ( part of the computer's firmware ) to achieve power management.

In this way the APM driver is an intermediary between the BIOS and the operating system.

In IBM PC compatible computers, the Basic Input / Output System ( BIOS ), also known as the system BIOS or ROM BIOS (), is a de facto standard defining a firmware interface.

The BIOS software is built into the PC, and is the first code run by a PC when powered on (' boot firmware ').

When the PC starts up, the first job for the BIOS is the power-on self-test, which initializes and identifies system devices such as the CPU, RAM, video display card, keyboard and mouse, hard disk drive, optical disc drive and other hardware.

BIOS software is stored on a non-volatile ROM chip on the motherboard.

As of 2011, the BIOS is being replaced by the more complex Extensible Firmware Interface ( EFI ) in many new machines, but BIOS remains in widespread use.

However, the distinction between BIOS and EFI is rarely made in terminology by the average computer user, making BIOS a catch-all term for both systems.

Most versions of DOS have a file called " IO. SYS ", " IBMBIO. COM ", " IBMBIO. SYS ", or " DRBIOS. SYS "; this file is known as the " DOS BIOS ", which is analogous to the " CP / M BIOS ".

In principle, a BIOS in ROM is customized to the particular manufacturer's hardware, allowing low-level services ( such as reading a keystroke or writing a sector of data to diskette ) to be provided in a standardized way to an operating system.

On many modern PCs, Pause interrupts screen output by BIOS until another key is pressed.

The CPU of the V64 is a 6502 chip ( the CPU from the Nintendo Entertainment System ); the operating system is stored in the BIOS chip.

When power is first applied to the motherboard, the BIOS firmware tests and configures memory, circuitry, and peripherals.

On recent motherboards, the BIOS may also patch the central processor microcode if the BIOS detects that the installed CPU is one in for which errata has been published.

) Windowed CERDIP-packaged PROMs were used for the BIOS ROM of many early IBM PC clones ( which were manufactured in limited enough quantities to make PROM an economical choice ) often with a foil-backed ( or regular paper ) adhesive label covering the window to prevent inadvertent erasure through exposure to ambient light.

This meant that by porting the limited number of simple routines in the BIOS to a particular hardware platform, the entire OS would work.

This is opposed to the " traditional " int 10h BIOS calls, which are limited to resolutions of 640 × 480 pixels with 16 color ( 4-bit ) depth or less.

For this reason, with very old BIOS, the accessible area is limited to cylinders 0 to 1023 of the first two hard disks.

* Added support for using the lower 32K RAM of the computer ( not directly visible because the BIOS and BASIC interpreter ROMs take over the addressing space ) as a limited RAM disk ( only certain types of files could be saved ).

Although the " Classic Mac OS " boot process is convoluted and largely undocumented, it is not more limited than an IBM PC compatible BIOS.

The separate slow DOS chip was a problem for owners who played DOS games because these chips were quite slow and had limited and buggy VESA BIOS Extensions implementations.

If the x86 processor supports this feature in hardware, and if the system's BIOS provides support for this feature and it has been enabled, either by the manufacturer or the user, then the NX features are turned on in Windows, on a limited " OptIn " basis.

In general, the vesa driver supports most graphics cards without acceleration and with display resolutions limited to a set of resolutions programmed in the video BIOS by the manufacturer.

16-bit BIOS interfaces are required by certain x86 operating systems, such as DOS and Windows 3. 1 / 95 / 98 ( and all when not booted via UEFI ).

However, most boot loaders retain 16-bit support BIOS call support.

Even further, " AT-class " became a term describing any machine which supported the BIOS functions, 16-bit expansion slots, keyboard interface, and other defining technical features of the IBM PC AT ; in the case of the expansion slots, the term is largely synonymous with " ISA " ( when the latter is not applied as a retronym to XT-class machines, as in the phrase " 8-bit ISA slot ".

While DJGPP runs in 32-bit protected mode, its stub and library heavily rely upon many 16-bit DOS and BIOS calls.

PC BIOS limitations ( 16-bit processor mode, 1 MB addressable space, PC AT hardware dependencies, etc.

NTVDM emulates BIOS calls and tables as well as the Windows 3. 1 kernel and 16-bit API stubs.

* SeaBIOS, a tiny implementation of x86 BIOS, written mostly in 16-bit C using the GNU C compiler.

The computer's BIOS is invoked during the 16-bit real mode bootstrap stage ; once in 32-bit mode, Singularity never invokes the BIOS again, but invokes device drivers written in Sing #.

Still later, popular usage extended the word " firmware " to denote anything ROM-resident, including processor machine-instructions for BIOS, bootstrap loaders, or specialized applications.

Several shortcomings such as the inability to access the BIOS or DOS calls due to inability to switch back to real mode without resetting the processor prevented widespread usage.

The processor supports Intel VT-x ; this is disabled in the BIOS but can be turned on thanks to a BIOS update.

The system BIOS ROMs must be at the upper end of the address space because the CPU starting address is fixed by the design of the processor.

Generally only system software, i. e. the BIOS, operating systems, and some specialized utility programs ( e. g., memory testers ), address physical memory using machine code operands or processor registers, instructing the CPU to direct a hardware device, called the memory controller, to use the memory bus or system bus, or separate control, address and data busses, to execute the program's commands.

Socket AM2 supports AMD Phenom processors but some motherboard manufacturers did not supply newer BIOS files required to operate a Phenom processor.

A software engineer was hired to write the special " dual boot mode " BIOS and the special CP / M BIOS.

The " dual boot mode " BIOS actually discovered whether a TRS-DOS, or Aster CP / M disk was placed in the drive, and would, depending on the type of disk, reorganise the internal memory architecture of the system, to either be 100 % TRS-80 compatible or optimally support CP / M, with as much " workspace " as possible, and the 80x25 video mode.

For example, an IBM PC might have either a monochrome or a color display adapter ( using different display memory addresses and hardware ), but a single, standard, BIOS system call may be invoked to display a character at a specified position on the screen in text mode.

( The DOS could utilize the additional RAM available in the protected mode — extended memory either via BIOS call ( INT 15h, AH = 87h ), or as RAM disk, or as emulation of expanded memory.

The graphics mode was rarely used either, as it was not supported by the BIOS.

Also coreboot allows a computer to boot without having the firmware / BIOS constantly running in system management mode.

A protected mode OS can also be written for the 80286, but DOS application compatibility was more difficult than expected, not only because most DOS applications accessed the hardware directly, bypassing BIOS routines intended to ensure compatibility, but also that most BIOS requests were made by interrupt vectors that were marked as " reserved " by Intel.

The PC BIOS which IBM introduced operates in real mode, as do the DOS operating systems ( MS-DOS, DR-DOS, etc .).

The switch to real mode is costly in terms of time, but this technique allows protected mode programs to use services such as BIOS, which runs entirely in real mode ( having been designed originally for the 8088-based IBM Personal Computer model ( machine type ) 5150 ).

This mode-switching technique is also the one used by DPMI ( under real, not emulated, DOS ) and DOS extenders like DOS / 4GW to allow protected mode programs to run under DOS ; the DPMI system or DOS extender switches to real mode to invoke DOS or BIOS calls, then switches back to return to the application program which runs in protected mode.

Programming for the Hercules card's native graphics mode was somewhat hindered by a lack of BIOS support and standardization from IBM — after all, the HGC was a competing technology.

Default VGA 256 color paletteMode 13h is the IBM VGA BIOS mode number for a specific standard 256 color mode on IBM's VGA graphics hardware.

It is not essential to set the graphics mode through the BIOS ; it is possible to switch graphics mode in 32-bit protected mode, if a little more complicated.

Set VGA graphics mode without BIOS in C