Operating system services BIOS

1 operating system services

1.1 processor microcode updates
1.2 identification
1.3 overclocking
1.4 modern use

operating system services

the bios rom customized particular manufacturer s hardware, allowing low-level services (such reading keystroke or writing sector of data diskette) provided in standardized way programs, including operating systems. example, ibm pc might have either monochrome or color display adapter (using different display memory addresses , hardware), single, standard, bios system call may invoked display character @ specified position on screen in text mode or graphics mode.

the bios provides small library of basic input/output functions operate peripherals (such keyboard, rudimentary text , graphics display functions , forth). when using ms-dos, bios services accessed application program (or ms-dos) executing int 13h interrupt instruction access disk functions, or executing 1 of number of other documented bios interrupt calls access video display, keyboard, cassette, , other device functions.

operating systems , executive software designed supersede basic firmware functionality provide replacement software interfaces application software. applications can provide these services themselves. began in 1980s under ms-dos, when programmers observed using bios video services graphics display slow. increase speed of screen output, many programs bypassed bios , programmed video display hardware directly. other graphics programmers, particularly not exclusively in demoscene, observed there technical capabilities of pc display adapters not supported ibm bios , not taken advantage of without circumventing it. since at-compatible bios ran in intel real mode, operating systems ran in protected mode on 286 , later processors required hardware device drivers compatible protected mode operation replace bios services.

in modern personal computers running modern operating systems bios used during booting , initial loading of system software. before operating system s first graphical screen displayed, input , output typically handled through bios. boot menu such textual menu of windows, allows users choose operating system boot, boot safe mode, or use last known configuration, displayed through bios , receives keyboard input through bios.

most modern pcs can still boot , run legacy operating systems such ms-dos or dr-dos rely heavily on bios console , disk i/o, providing system has bios or bios-compatible firmware, not case uefi-based pcs.

processor microcode updates

intel processors have reprogrammable microcode since p6 microarchitecture. bios may contain patches processor microcode fix errors in initial processor microcode; reprogramming not persistent, loading of microcode updates performed each time system powered up. without reprogrammable microcode, expensive processor swap required; example, pentium fdiv bug became expensive fiasco intel required product recall because original pentium processor s defective microcode not reprogrammed.

identification

some bioses contain software licensing description table (slic), digital signature placed inside bios original equipment manufacturer (oem), example dell. slic inserted acpi table , contains no active code.

computer manufacturers distribute oem versions of microsoft windows , microsoft application software can use slic authenticate licensing oem windows installation disk , system recovery disc containing windows software. systems slic can preactivated oem product key, , verify xml formatted oem certificate against slic in bios means of self-activating (see system locked preinstallation, slp). if user performs fresh install of windows, need have possession of both oem key (either slp or coa) , digital certificate slic in order bypass activation. can achieved if user performs restore using pre-customised image provided oem. power users can copy necessary certificate files oem image, decode slp product key, perform slp activation manually. cracks non-genuine windows distributions edit slic or emulate in order bypass windows activation.

overclocking

some bios implementations allow overclocking, action in cpu adjusted higher clock rate manufacturer rating guaranteed capability. overclocking may, however, compromise system reliability in insufficiently cooled computers , shorten component lifespan. overclocking, when incorrectly performed, may cause components overheat mechanically destroy themselves.

modern use

some operating systems, example ms-dos, rely on bios carry out input/output tasks within pc.

because bios still runs in 16-bit real mode, calling bios services directly inefficient protected-mode operating systems. bios services not used modern multitasking operating systems after load, importance of primary part of bios reduced initially.

later bios implementations took on more complex functions, including interfaces such advanced configuration , power interface (acpi); these functions include power management, hot swapping, , thermal management. @ same time, since 2010, bios technology in transitional process toward uefi.