十二 02

What’s Just a BIOS and What Can You Do?

作者: yangshuang 分类:CTO视点   阅读:24 次 添加评论

In computing, BIOS (/ ˈbaɪɒs, -oʊs/, BY-oss, -ohss; an acronym for Fundamental Input/Output System and also called the System BIOS, ROM BIOS or COMPUTER BIOS) is firmware utilized to perform equipment initialization during the booting procedure (power-on startup), as well as to supply runtime services for operating systems and programs. The BIOS firmware comes pre-installed on a personal computer's system board, and it is the very first software to run when powered on. The name originates from the Fundamental Input/Output System made use of in the CP/M operating system in 1975. The BIOGRAPHY initially exclusive to the IBM PC has actually been reverse crafted by some business (such as Phoenix metro Technologies) looking to produce compatible systems. The interface of that initial system acts as a de facto criterion.

The BIOGRAPHY in contemporary PCs initializes and also examines the system equipment elements, as well as loads a boot loader from a mass memory gadget which then initializes an os. In the period of DOS, the BIOS provided BIOS disrupt ask for the key-board, screen, and also various other input/output (I/O) devices that standard an interface to application programs and also the os. Much more recent os do not use the BIOGRAPHY disturb calls after start-up.

Most BIOS implementations are particularly created to work with a specific computer system or motherboard model, by interfacing with various gadgets that make up the corresponding system chipset. Initially, BIOGRAPHY firmware was kept in a ROM chip on the COMPUTER motherboard. In contemporary computer system systems, the BIOS components are kept on flash memory so it can be revised without getting rid of the chip from the motherboard. This permits very easy, end-user updates to the BIOS firmware so brand-new attributes can be added or pests can be fixed, yet it likewise creates an opportunity for the computer to become infected with BIOGRAPHY rootkits. In addition, a BIOS upgrade that fails might brick the motherboard.

Unified Extensible Firmware User Interface (UEFI) is a follower to the legacy COMPUTER BIOGRAPHIES, aiming to resolve its technological restrictions.

Background

The term BIOGRAPHY (Basic Input/Output System) was created by Gary Kildall and first appeared in the CP/M os in 1975, explaining the machine-specific part of CP/M packed during boot time that interfaces directly with the equipment. (A CP/M equipment typically has only a basic boot loader in its ROM.).

Versions of MS-DOS, COMPUTER DOS or DR-DOS contain a documents called otherwise "IO.SYS", "IBMBIO.COM", "IBMBIO.SYS", or "DRBIOS.SYS"; this documents is known as the "DOS BIOS" (also referred to as the "DOS I/O System") as well as consists of the lower-level hardware-specific part of the os. Along with the underlying hardware-specific but operating system-independent "System BIOS", which resides in ROM, it stands for the analogue to the "CP/M BIOS".

The BIOGRAPHY initially exclusive to the IBM PC has been reverse crafted by some firms (such as Phoenix metro Technologies) looking to develop suitable systems.

With the intro of PS/2 devices, IBM divided the System BIOS into real- and also protected-mode sections. The real-mode section was meant to supply backwards compatibility with existing os such as DOS, and consequently was called "CBIOS" (for "Compatibility BIOS"), whereas the "ABIOS" (for "Advanced BIOS") gave new interfaces specifically suited for multitasking operating systems such as OS/2.

Interface

The BIOGRAPHY of the original IBM PC and XT had no interactive interface. Error codes or messages were shown on the display, or coded series of sounds were produced to signify mistakes when the power-on self-test (BLOG POST) had actually not continued to the point of efficiently booting up a video display adapter. Options on the IBM PC as well as XT were set by buttons and jumpers on the major board as well as on development cards. Beginning around the mid-1990s, it came to be normal for the BIOS ROM to consist of a "BIOS arrangement utility" (BCU [12] or "BIOS configuration energy", accessed at system power-up by a certain essential series. This program permitted the customer to set system arrangement alternatives, of the type formerly established making use of DIP buttons, via an interactive menu system regulated through the key-board. In the interim period, IBM-compatible PCs– consisting of the IBM AT– held arrangement setups in battery-backed RAM as well as utilized a bootable configuration program on disk, not in the ROM, to set the arrangement alternatives consisted of in this memory. The disk was provided with the computer system, as well as if it was shed the system settings could not be transformed. The very same applied in general to computer systems with an EISA bus, for which the arrangement program was called an EISA Setup Energy (ECU).

A modern-day Wintel-compatible computer system gives an arrangement routine essentially the same in nature from the ROM-resident BIOGRAPHY arrangement utilities of the late 1990s; the individual can set up equipment choices utilizing the key-board and also video display. Likewise, when errors take place at boot time, a modern BIOGRAPHY generally presents easy to use error messages, typically offered as pop-up boxes in a TUI style, and supplies to get in the BIOS setup energy or to neglect the mistake and proceed ideally. As opposed to battery-backed RAM, the modern-day Wintel device might save the BIOGRAPHY configuration setups in flash ROM, maybe the exact same flash ROM that holds the BIOS itself.

Procedure

System startup

Early Intel processors began at physical address 000FFFF0h. Solutions with later cpus offer logic to begin running the BIOS from the system ROM.
If the system has just been powered up or the reset button was pushed (" cold boot"), the full power-on self-test (BLOG POST) is run. If Ctrl+ Alt+ Erase was pushed (" warm boot"), an unique flag value stored in nonvolatile BIOGRAPHIES memory (" CMOS") examined by the BIOS allows bypass of the extensive BLOG POST and also memory detection.

The ARTICLE identifies, as well as initializes system tools such as the CPU, RAM, interrupt controllers, DMA controllers, chipset, video display card, key-board, disk drive, optical disc drive and various other hardware.

Early IBM PCs had a routine in the MESSAGE that would certainly download a program into RAM via the keyboard port and run it. This attribute was meant for manufacturing facility examination or diagnostic objectives.

Boot procedure

After the alternative ROM scan is completed and all found ROM modules with legitimate checksums have been called, or instantly after MESSAGE in a BIOS variation that does not check for option ROMs, the BIOS calls INT 19h to begin boot handling. Post-boot, programs filled can additionally call INT 19h to reboot the system, yet they have to be careful to disable disrupts and other asynchronous hardware processes that may disrupt the BIOS restarting procedure, otherwise the system may hang or collapse while it is restarting.

When INT 19h is called, the BIOS attempts to situate boot loader software on a "boot tool", such as a hard drive, a floppy disk, CD, or DVD. It loads and implements the initial boot software it locates, giving it control of the PC.

The BIOS makes use of the boot tools embeded in EEPROM, CMOS RAM or, in the earliest PCs, DIP switches. The BIOGRAPHY checks each gadget in order to see if it is bootable by trying to fill the first field (boot sector). If the industry can not be read, the BIOS continues to the following gadget. If the industry is read efficiently, some BIOSes will additionally check for the boot industry trademark 0×55 0xAA in the last 2 bytes of the industry (which is 512 bytes long), prior to accepting a boot market and also taking into consideration the tool bootable.

When a bootable tool is found, the BIOS transfers control to the packed sector. The BIOS does not analyze the components of the boot industry besides to possibly check for the boot sector trademark in the last 2 bytes. Interpretation of information structures like dividing tables and also BIOGRAPHIES Parameter Blocks is done by the boot program in the boot sector itself or by various other programs filled through the boot procedure.

A non-disk device such as a network adapter attempts starting by a treatment that is specified by its option ROM or the comparable incorporated into the motherboard BIOGRAPHY ROM. Therefore, option ROMs might additionally affect or replace the boot procedure specified by the motherboard BIOS ROM.

Boot concern

The individual can pick the boot top priority applied by the BIOS. For instance, a lot of computers have a hard disk that is bootable, however typically there is a removable-media drive that has higher boot priority, so the customer can create a detachable disk to be started.

In many modern-day BIOSes, the boot concern order can be set up by the customer. In older BIOSes, restricted boot top priority options are selectable; in the earliest BIOSes, a fixed top priority scheme was carried out, with floppy disk drives first, fixed disks (i.e. hard disks) 2nd, as well as generally no other boot devices supported, subject to modification of these guidelines by set up choice ROMs. The BIOS in a very early PC also generally would only boot from the very first floppy disk drive or the very first hard disk drive, even if there were 2 drives mounted.

With the El Torito optical media boot requirement, the optical drive actually replicates a 3.5" high-density floppy disk to the BIOGRAPHY for boot objectives. Reading the "very first industry" of a CD-ROM or DVD-ROM is not a just specified operation like it is on a floppy disk or a hard disk. Moreover, the complexity of the medium makes it difficult to create a valuable boot program in one market. The bootable online floppy can contain software program that supplies accessibility to the optical tool in its native style.

Expansions (choice ROMs)

Peripheral cards such as some disk drive controllers as well as some video display adapters have their very own scph1001.bin extension alternative ROMs, which provide extra performance to BIOGRAPHY. Code in these expansions runs prior to the BIOS boots the system from mass storage space. These ROMs normally examination and boot up hardware, add brand-new BIOGRAPHIES solutions, and also augment or change existing BIOGRAPHIES services with their own variations of those solutions. For example, a SCSI controller normally has a BIOS expansion ROM that adds support for hard disks connected via that controller. Some video cards have extension ROMs that replace the video services of the motherboard BIOS with their own video solutions. BIOS extension ROMs gain total control of the machine, so they can in fact do anything, and also they may never return control to the BIOS that invoked them. An expansion ROM could in concept have an entire operating system or an application program, or it can apply a completely different boot process such as starting from a network. Procedure of an IBM-compatible computer system can be entirely altered by removing or placing an adapter card (or a ROM chip) that contains a BIOGRAPHY expansion ROM.

The motherboard BIOGRAPHY normally has code to accessibility equipment components essential for bootstrapping the system, such as the key-board, display screen, and storage. In addition, plug-in adapter cards such as SCSI, RAID, network interface cards, as well as video boards frequently include their own BIOS (e.g. Video clip BIOS), complementing or changing the system BIOS code for the given component. Also gadgets built into the motherboard can behave in this way; their alternative ROMs can be kept as separate code on the main BIOS blink chip, as well as updated either in tandem with, or independently from, the primary BIOGRAPHIES.

An add-in card calls for an option ROM if the card is not sustained by the primary BIOS as well as the card needs to be booted up or made easily accessible via BIOGRAPHY services prior to the operating system can be loaded (usually this suggests it is called for in the bootstrapping procedure). Also when it is not required, an alternative ROM can permit an adapter card to be used without packing chauffeur software application from a storage device after starting starts– with an option ROM, no time at all is required to load the vehicle driver, the motorist does not use up room in RAM nor on hard disk, and also the motorist software application on the ROM always sticks with the gadget so both can not be unintentionally divided. Additionally, if the ROM is on the card, both the outer equipment as well as the vehicle driver software program offered by the ROM are installed together with no added effort to set up the software application. An additional benefit of ROM on some early COMPUTER systems (especially including the IBM PCjr) was that ROM was faster than major system RAM. (On contemporary systems, the case is significantly the opposite of this, as well as BIOGRAPHY ROM code is typically duplicated (" shadowed") into RAM so it will run quicker.).

There are many methods as well as energies for analyzing the components of various motherboard BIOS and expansion ROMs, such as Microsoft DEBUG or the Unix dd.

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