MSI MS-9282 Dokumentacja Pobierz pdf (Strona 8)

An add-in card requires an option ROM if the card is not supported by the main BIOS and the card
needs to be initialized or made accessible through BIOS services before the operating system can be
loaded (usually this means it is required in the bootstrapping process). Even when it is not required, an
option ROM can allow an adapter card to be used without loading driver software from a storage
device after booting begins – with an option ROM, no time is taken to load the driver, the driver does
not take up space in RAM nor on hard disk, and the driver software on the ROM always stays with the
device so the two cannot be accidentally separated. Also, if the ROM is on the card, both the
peripheral hardware and the driver software provided by the ROM are installed together with no extra
effort to install the software. An additional advantage of ROM on some early PC systems (notably
including the IBM PCjr) was that ROM was faster than main system RAM. (On modern systems, the
case is very much the reverse of this, and BIOS ROM code is usually copied ("shadowed") into RAM
so it will run faster.)
There are many methods and utilities for examining the contents of various motherboard BIOS and
expansion ROMs, such as Microsoft DEBUG or the Unix dd.
If an expansion ROM wishes to change the way the system boots (such as from a network device or a
SCSI adapter for which the BIOS has no driver code) in a cooperative way, it can use the BIOS Boot
Specification (BBS) API to register its ability to do so. Once the expansion ROMs have registered
using the BBS APIs, the user can select among the available boot options from within the BIOS's user
interface. This is why most BBS compliant PC BIOS implementations will not allow the user to enter
the BIOS's user interface until the expansion ROMs have finished executing and registering
themselves with the BBS API. The specification can be downloaded from the ACPICA website. The
official title is BIOS Boot Specification (Version 1.01, 11 January 1996).
[10]
Also, if an expansion ROM wishes to change the way the system boots unilaterally, it can simply hook
INT 19h or other interrupts normally called from interrupt 19h, such as INT 13h, the BIOS disk
service, to intercept the BIOS boot process. Then it can replace the BIOS boot process with one of its
own, or it can merely modify the boot sequence by inserting its own boot actions into it, by preventing
the BIOS from detecting certain devices as bootable, or both. Before the BIOS Boot Specification was
promulgated, this was the only way for expansion ROMs to implement boot capability for devices not
supported for booting by the native BIOS of the motherboard.
Operating system services
The BIOS 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 programs, including operating systems. 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 or graphics mode.
The BIOS provides a small library of basic input/output functions to operate peripherals (such as the
keyboard, rudimentary text and graphics display functions and so forth). When using MS-DOS, BIOS
services could be accessed by an application program (or by MS-DOS) by executing an INT 13h
interrupt instruction to access disk functions, or by executing one of a number of other documented
BIOS interrupt calls to access video display, keyboard, cassette, and other device functions.
Operating systems and executive software that are designed to supersede this basic firmware
functionality provide replacement software interfaces to application software. Applications can also
provide these services to themselves. This began even in the 1980s under MS-DOS, when
1 2 3 4 5 6 7 8 9 10 11 12 13 ... 19 20
Komentarze do niniejszej Instrukcji

Brak uwag
MSI MS-9282 Dokumentacja Strona 8

Komentarze do niniejszej Instrukcji

Powiązane produkty i podręczniki dla Serwery MSI MS-9282
