BIOS - all about it

RO(Romanian)
BIOSul (Basic Input Output System) este o componentă a calculatoarelor care face legătura dintre componentele fizice (hardware) și sistemul de operare utilizat de către mașina respectivă.

Câteva dintre companiile producătoare de BIOS-uri sunt: Award, AMI și Phoenix.

BIOS-ul îndeplinește trei funcții fundamentale:

Controlul dispozitivelor la pornire POST
Încărcarea sistemelor de operare
Face legătură între sistemul de operare și unele dispozitive fizice (așa numitul hardware)

[modifică]Noțiuni teoretice
Sistemul de bază de intrare/ieșire (BIOS –Basic Input/Output Sistem) pentru calculatoarele personale ale familiei IBM PC și IBM PS/2 – este o interfață de programe între programe și partea fizică a calculatorului personal.

BIOS–ul izolează sistemul de operare și programele din mașină de particularitățile tehnice ale dispozitivelor fizice concrete și permite programatorilor să folosească operații de Intrare/Ieșire în interiorul programelor pe care le creează, fără a lua în seamă adresele dispozitivelor sau caracteristicile tehnice ale masinii. Pentru a fi performant și rentabil, programul trebuie gândit pentru toate tipurile de arhitecturi fizice, pentru a putea fi executat sub orice platformă fizică sau software, condiție numită portabilitate, și care separă limbajele de programare de nivel jos (Asamblare) de cele de nivel înalt (tip C, C++, Java).

În afară de aceasta, BIOS-ul asigură un șir de servicii de sistem; de exemplu, permite a se afla dimensiunile memoriei calculatorului personal sau data și ora zilei curente, sau configura modul in care se folosesc dispozitivele fizice în momentul pornirii mașinii etc. Se recomandă de a efectua accesul la BIOS nu prin manipulare directă ci prin porturile de Intrare/Ieșire la scrierea atât a programelor de sistem cât și a programelor aplicații.

Programarea la nivelul BIOS-lui micșorează dependența programelor de schimbarea parametrilor tehnici ai calculatorului personal și prin aceasta mărește mobilitatea lor. Funcțiile de bază al BIOS–ului se caracterizează prin:

testarea calculatorului personal la punerea în priză
asigurarea controlului dispozitivele externe
servicii de sistem


BIOS-ul (Basic Input Output System) are mai multe roluri, dar cel mai important se refera la apelarea tuturor componentelor conectate la placa de bază. Cand computerul este pornit, infor maţia de la harddisk nu poate ajunge la procesor (CPU) şi, implicit, sistemul de operare nu poate fi încărcat fără instruc ţiunile furnizate de BIOS.

BIOS-ul realizeaza de asemenea un test ca re verifica dacă totul merge aşa cum tre buie, citirea informaţiei de la alte cipuri BIOS care iniţializează alte plăci (de exemplu placa grafică), mai multe co­menzi pe care sistemul de operare le va folosi pentru a lucra cu diferitele compo nente hardware, setări pentru harddisk, ceasul intern etc.

BIOS-ul a fost introdus la scară largă de către IBM, în urmă cu aproape 25 de ani, odată cu primele PC-uri. La acea vreme era una dintre puţinele soluţii care presu punea un nivel de abstractizare indepen dent de sistemul de operare. Acest nivel deservea sistemul cu o serie de funcţii de bază, rea liza paşii necesari încărcării sistemului de operare şi, totodată, punea la dispoziţie unele opţiuni de configurare.

BIOS-ul, din punct de vedere fizic, este un cip aflat pe placa de bază, care are grijă ca toate ele mentele componente ale calculatorului, la pornire, să funcţioneze împreună. îna inte ca sistemul de operare să fie încărcat este iniţializat BIOS-ul care, prin inter mediul rutinelor de bază (intrare/ieşire), asigură comunicarea între componentele hardware instalate în sistem.

Iniţial, acest cip era o memorie ROM, dar pentru că în aceste condiţii era mai greu de actualizat, mediul de stocare a fost înlocuit de memoria EEPROM, de numită şi flash ROM. Cipul este montat pe un soclu, pentru a fi mai uşor de înlo uit, ca orice altă componenta. In momentul de fata exista trei mari producători de cipuri BIOS mai cunos cuţi, şi anume Phoenix Technologies, AWARD Software şi AMI(American Me-gatrends Inc.). In general, producătorii de plăci de bază optează pentru unul din tre aceştia trei.

Controlul chipset-ului

Aici se regasesc cele mai importante setari ce controleaza functionarea chipset-ului si componentelor cu care acesta are o relatie directa, si anume memoria RAM si placa grafica. „Memory timings" este sectiunea in care se pot face modificarile cele mai importante ale timpilor si caracteristicilor de functionare ale memoriei. Aceste modificari trebuie facute in directa concordanta cu specificatiile memoriilor. Un caz util in care se pot aduce asemenea modificari este, de exemplu, in cazul in care un utilizator decide sa-si seteze memoriile in mod sincron cu FSB-ul procesorului si trebuie sa scada frecventa memoriilor pentru aceasta. In acest caz o memorie care specifica latentele 2,5-3-3-7 la 400 MHz functioneaza perfect la 333 MHz in latente 2-3-3-6. Acest lucru nu este overclocking, la fiecare frecventa o memorie poate suporta alte latente.

In majoritatea cazurilor sunt disponibile patru tipuri de caracteristici ce pot fi modificate: „DRAM active precharge delay", „DRAM RAS to CAS delay", „DRAM RAS precharge delay" si „DRAM CAS latency". „DRAM active delay". Pentru a intelege functionarea acestor timpi trebuie mai intai sa cunoastem cate ceva despre functionarea memoriei RAM. Aceasta poate fi conceputa ca o matrice, cu randuri si coloane. Citirea sau scrierea in memoria RAM se face activand coloanele in care se afla datele necesare, si apoi citirea lor in rafala. Toate operatiunile au un numar de batai de ceas alocate.

„DRAM RAS to CAS delay" este timpul masurat in cicluri sau batai de ceas intre semnalele RAS si CAS, si are loc de fiecare data cand un rand este reimprospatat sau activat. Reducerea acestui timp duce la o performanta mai mare. Valorile comune sunt 3 sau 4, dar exista memorii ce suporta si valoarea 2. „DRAM RAS precharge delay" determina numarul de cicluri necesar pana la o noua operatiune RAS, deci pana la activarea unui nou rand. Valorile cele mai comune sunt 3 sau 4, dar la memoriile care suporta o valoare de 2, aceasta duce la o marire a performantei. Fortarea memoriei pentru o valoare pe care nu o suporta, duce la coruperea datelor in randul din care se citeste, pentru ca acesta devine inactiv inainte sa se termine rescrierea lui.

„DRAM CAS latency" este cel mai important parametru al unei memorii, si modificarea acestuia are cel mai mare impact asupra performantei sistemului. Aceasta setare modifica latenta in numar de cicluri de cand este aplicat semnalul CAS si pana cand datele din sectorul de memorie vizat devin disponibile. De asemenea, aceasta valoare determina si timpul maxim, in numar de cicluri, in care se poate face un transfer in rafala din respectivul sector de memorie.

In „Advanced chipset features" mai regasim si o setare ce priveste subsistemul grafic, care este numita „AGP aperture size". Aceasta controleaza doi parametri: marimea aperturii AGP si dimensiunea GART (Graphics Adress Relocation Table). Apertura AGP este o portiune din memoria sistemului ce face parte din raza de actiune a memoriei ce poate fi adresata direct de catre controlerul PCI. Memoria folosita de apertura este de obicei fragmentata, deoarece RAM-ul este folosit si de sistem si atunci GART-ul face translatia intre adresele fizice ale memoriei RAM si adresele virtuale folosite de subsistemul grafic. De obicei, spatiul necesar aperturii AGP se micsoreaza odata cu cantitatea de memorie prezenta pe placa grafica, dar este bine sa fie pastrata o valoare de 64 sau 128 MB pentru fluidizarea transferului pe AGP si pastrarea la o dimensiune rezonabila a adreselor GART. „AGP fast write" este o alta optiune ce are ca obiect subsistemul grafic, activarea acesteia ducand la optimizarea transferurilor dinspre chipset catre acceleratorul grafic, deoarece acesta se comporta ca un dispozitiv PCI. Este recomandata activarea acestei optiuni deoarece se observa un spor de performanta la citirea datelor. In cazul in care exista un dispozitiv PCI care incepe sa nu se mai comporte normal, aceasta trebuie dezactivata.

„AGP spread spectrum" este o optiune care nu are legatura directa cu performanta sistemului. Aceasta optiune realizeaza modularea frecventelor folosite de AGP, pentru a nu emite radiatii electromagnetice ce pot afecta alte componente. Multi dintre utilizatorii ce nu folosesc aceasta optiune, aud un bazait generat de placa de sunet on-board, care, de obicei, nu are filtrare EMI suficienta.


EN(English)
In IBM PC Compatible computers, the binary input/output system (BIOS)[1] , also known as the System BIOS, is a de facto standard defining a firmware interface.[2]


Phoenix AwardBIOS CMOS (non-volatile memory) Setup utility on a standard PC
The BIOS of a PC software is built into the PC, and is the first code run by a PC when powered on ('boot firmware'). The primary function of the BIOS is to load and start an operating system. When the PC starts up, the first job for the BIOS is to initialize and identify system devices such as the video display card, keyboard and mouse, hard disk, CD/DVD drive and other hardware. The BIOS then locates software held on a peripheral device (designated as a 'boot device'), such as a hard disk or a CD, and loads and executes that software, giving it control of the PC.[3] This process is known as booting, or booting up, which is short for bootstrapping.


BIOS software is stored on a non-volatile ROM chip built into the system on the mother board. The BIOS software is specifically designed to work with the particular type of system in question, including having a knowledge of the workings of various devices that make up the complementary chipset of the system. In modern computer systems, the BIOS chip's contents can be rewritten allowing BIOS software to be upgraded.

A BIOS will also have a user interface (or UI for short). Typically this is a menu system accessed by pressing a certain key on the keyboard when the PC starts. In the BIOS UI, a user can:

configure hardware
set the system clock
enable or disable system components
select which devices are eligible to be a potential boot device
set various password prompts, such as a password for securing access to the BIOS UI functions itself and preventing malicious users from booting the system from unauthorized peripheral devices.
The BIOS provides a small library of basic input/output functions used to operate and control the peripherals such as the keyboard, text display functions and so forth, and these software library functions are callable by external software. In the IBM PC and AT, certain peripheral cards such as hard-drive controllers and video display adapters carried their own BIOS extension ROM, which provided additional functionality. Operating systems and executive software, designed to supersede this basic firmware functionality, will provide replacement software interfaces to applications.

The role of the BIOS has changed over time; today BIOS is a legacy system, superseded by the more complex Extensible Firmware Interface (EFI), but BIOS remains in widespread use, and EFI booting has only been supported in x86 Windows since 2008. BIOS is primarily associated with the 16-bit and 32-bit architecture eras (x86-32), while EFI is used for some 32-bit and most 64-bit architectures. Today BIOS is primarily used for booting a system, and for certain additional features such as power management (ACPI) and video initialization (in X.org), but otherwise is not used during the ordinary running of a system, while in early systems (particularly in the 16-bit era), BIOS was used for hardware access – operating systems (notably MS-DOS) would call the BIOS rather than directly accessing the hardware. In the 32-bit era and later, operating systems instead generally directly accessed the hardware using their own device drivers. However, the distinction between BIOS and EFI are rarely made in terminology by the average computer user, making BIOS a catch-all term for both systems.





Terminology
The term first appeared in the CP/M operating system, describing the part of CP/M loaded during boot time that interfaced directly with the hardware (CP/M machines usually had only a simple boot loader in their ROM). Most versions of DOS have a file called "IBMBIO.COM" or "IO.SYS" that is analogous to the CP/M BIOS.

Among other classes of computers, the generic terms boot monitor, boot loader or boot ROM were commonly used. Some Sun and PowerPC-based computers use Open Firmware for this purpose. There are a few alternatives for Legacy BIOS in the x86 world: Extensible Firmware Interface, Open Firmware (used on the OLPC XO-1) and coreboot.





IBM PC-compatible BIOS chips
In principle, the BIOS in ROM was 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 the operating system. For example, an IBM PC might have had either a monochrome or a color display adapter, using different display memory addresses and hardware - but the BIOS service to print a character on the screen in text mode would be the same.



PhoenixBIOS D686. This BIOS chip is housed in a PLCCpackage, which is, in turn, plugged into a PLCC socket.
Prior to the early 1990s, BIOSes were stored in ROM or PROM chips, which could not be altered by users. As its complexity and need for updates grew, and re-programmable parts became more available, BIOS firmware was most commonly stored on EEPROM or flash memory devices. According to Robert Braver, the president of the BIOS manufacturer Micro Firmware, Flash BIOS chips became common around 1995 because the electrically erasable PROM (EEPROM) chips are cheaper and easier to program than standard erasable PROM (EPROM) chips. EPROM chips may be erased by prolonged exposure to ultraviolet light, which accessed the chip via the window. Chip manufacturers use EPROM programmers (blasters) to program EPROM chips. Electrically erasable (EEPROM) chips come with the additional feature of allowing a BIOS reprogramming via higher-than-normal amounts of voltage.[4] BIOS versions are upgraded to take advantage of newer versions of hardware and to correct bugs in previous revisions of BIOSes.[5]

Beginning with the IBM AT, PCs supported a hardware clock settable through BIOS. It had a century bit which allowed for manually changing the century when the year 2000 happened. Most BIOS revisions created in 1995 and nearly all BIOS revisions in 1997 supported the year 2000 by setting the century bit automatically when the clock rolled past midnight, December 31, 1999.[6]

The first flash chips were attached to the ISA bus. Starting in 1997, the BIOS flash moved to the LPC bus, a functional replacement for ISA, following a new standard implementation known as "firmware hub" (FWH). In 2006, the first systems supporting a Serial Peripheral Interface (SPI) appeared, and the BIOS flash moved again.

The size of the BIOS, and the capacities of the ROM, EEPROM and other media it may be stored on, has increased over time as new features have been added to the code; BIOS versions now exist with sizes up to 16 megabytes. Some modern motherboards are including even bigger NAND Flash ROM ICs on board which are capable of storing whole compact operating system distribution like some Linux distributions. For example, some recent ASUS motherboards included SplashTop Linux embedded into their NAND Flash ROM ICs.



Flashing the BIOS
In modern PCs the BIOS is stored in rewritable memory, allowing the contents to be replaced or 'rewritten'. This rewriting of the contents is sometimes termed 'flashing'. This is done by a special program, usually provided by the system's manufacturer. A file containing such contents is sometimes termed 'a BIOS image'. A BIOS might be reflashed in order to upgrade to a newer version to fix bugs or provide improved performance or to support newer hardware, or a reflashing operation might be needed to fix a damaged BIOS.



BIOS chip vulnerabilities

An American Megatrends BIOS registering the "Intel CPU uCode Error" while doing POST, most likely a problem with the POST.
EEPROM chips are advantageous because they can be easily updated by the user; hardware manufacturers frequently issue BIOS updates to upgrade their products, improve compatibility and remove bugs. However, this advantage had the risk that an improperly executed or aborted BIOS update could render the computer or device unusable. To avoid these situations, more recent BIOSes use a "boot block"; a portion of the BIOS which runs first and must be updated separately. This code verifies if the rest of the BIOS is intact (using hash checksums or other methods) before transferring control to it. If the boot block detects any corruption in the main BIOS, it will typically warn the user that a recovery process must be initiated by booting from removable media (floppy, CD or USB memory) so the user can try flashing the BIOS again. Some motherboards have a backup BIOS (sometimes referred to as DualBIOS boards) to recover from BIOS corruptions.



Overclocking
Some BIOS chips allow overclocking, an action in which the CPU is adjusted to a higher clock rate than its factory preset. Overclocking may, however, seriously compromise safety in insufficiently cooled computers and generally shorten component lifespan.



Virus attacks
There are at least three known BIOS attack viruses.



CIH
The first was a virus which was able to erase Flash ROM BIOS content, rendering computer systems unstable. CIH, also known as "Chernobyl Virus", appeared for the first time in mid-1998 and became active in April 1999. It affected systems' BIOS and often could not be fixed on their own since they were no longer able to boot at all. To repair this, Flash ROM IC had to be ejected from the motherboard to be reprogrammed somewhere else. Damage from CIH was possible since the Virus was specifically targeted at the then widespread Intel i430TX motherboard chipset, and the most common operating systems of the time were based on the Windows 9x family allowing direct hardware access to all programs.

Modern systems are not vulnerable to CIH because of a variety of chipsets being used which are incompatible with the Intel i430TX chipset, and also other Flash ROM IC types. There is also extra protection from accidental BIOS rewrites in the form of boot blocks which are protected from accidental overwrite or dual and quad BIOS equipped systems which may, in the event of a crash, use a backup BIOS. Also, all modern operating systems like Linux, Mac OS X, Windows NT-based Windows OS like Windows 2000, Windows XP and newer, do not allow user mode programs to have direct hardware access. As a result, as of 2008, CIH has become essentially harmless, at worst causing annoyance by infecting executable files and triggering alerts from antivirus software. Other BIOS viruses remain possible, however[7]: since most Windows users run all applications with administrative privileges, a modern CIH-like virus could, in principle, still gain access to hardware.



Black Hat 2006
The second one was a technique presented by John Heasman, principal security consultant for UK based Next-Generation Security Software at the Black Hat Security Conference (2006), where he showed how to elevate privileges and read physical memory, using malicious procedures that replaced normal ACPI functions stored in flash memory.



Persistent BIOS Infection
The third one, known as "Persistent BIOS infection", was a method presented in CanSecWest Security Conference (Vancouver, 2009) and SyScan Security Conference (Singapore, 2009) where researchers Anibal Sacco [8] and Alfredo Ortega, from Core Security Technologies, demonstrated insertion of malicious code into the decompression routines in the BIOS, allowing for nearly full control of the PC at every start-up, even before the operating system is booted.

The proof-of-concept does not exploit a flaw in the BIOS implementation, but only involves the normal BIOS flashing procedures. Thus, it requires physical access to the machine or for the user on the operating system to be root. Despite this, however, researchers underline the profound implications of their discovery: "We can patch a driver to drop a fully working rootkit. We even have a little code that can remove or disable antivirus."[9]



Firmware on adapter cards
A computer system can contain several BIOS firmware chips. The motherboard BIOS typically contains code to access hardware components absolutely necessary for bootstrapping the system, such as the keyboard (either PS/2 or on a USB human interface device), and storage (floppy drives, if available, and IDE or SATA hard disk controllers). In addition, plug-in adapter cards such as SCSI,RAID, Network interface cards, and video boards often include their own BIOS (e.g. Video BIOS), complementing or replacing the system BIOS code for the given component. (This code is generally referred to as an option ROM.) Even devices built into the motherboard can behave in this way; their option ROMs can be stored as separate code on the main BIOS flash chip, and upgraded either in tandem with, or separately to, the main BIOS.

An add-in card usually only requires an option ROM if it:

Needs to be used before the operating system can be loaded (usually this means it is required in the bootstrapping process), and
Is too sophisticated or specific a device to be handled by the main BIOS
Older PC operating systems, such as MS-DOS (including all DOS-based versions of Microsoft Windows), and early-stage bootloaders, may continue to use the BIOS for input and output. However, the restrictions of the BIOS environment means that modern OSes will almost always use their own device drivers to directly control the hardware. Generally, these device drivers only use BIOS and option ROM calls for very specific (non-performance-critical) tasks, such as preliminary device initialization.

In order to discover memory-mapped option ROMs during the boot process, PC BIOS implementations scan real memory from 0xC0000 to 0xF0000 on 2 KiB boundaries, looking for a ROMsignature: 0xAA55 (0x55 followed by 0xAA, since the x86 architecture is little-endian). In a valid expansion ROM, this signature is immediately followed by a single byte indicating the number of 512-byte blocks it occupies in real memory. The next byte contains an offset describing the option ROM's entry point, to which the BIOS immediately transfers control. At this point, the expansion ROM code takes over, using BIOS services to register interrupt vectors for use by post-boot applications, provide a user configuration interface, or display diagnostic information.

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.



BIOS boot specification
If the 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), 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.[citation needed]



Changing role of the BIOS
Some operating systems, for example MS-DOS, rely on the BIOS to carry out most input/output tasks within the PC.[10] A variety of technical reasons makes it inefficient for some recent operating systems written for 32-bit CPUs such as Linux and Microsoft Windows to invoke the BIOS directly. Larger, more powerful, servers and workstations using PowerPC or SPARC CPUs by several manufacturers developed a platform-independent Open Firmware (IEEE-1275), based on the Forth programming language. It is included with Sun's SPARC computers, IBM's RS/6000 line, and other PowerPC CHRP motherboards. Later x86-based personal computer operating systems, like Windows NT, use their own, native drivers which also makes it much easier to extend support to new hardware, while the BIOS still relies on a legacy 16-bit runtime interface.

There was a similar transition for the Apple Macintosh, where the system software originally relied heavily on the ToolBox—a set of drivers and other useful routines stored in ROM based on Motorola's 680x0 CPUs. These Apple ROMs were replaced by Open Firmware in the PowerPC Macintosh, then EFI in Intel Macintosh computers.

Later BIOS took on more complex functions, by way of interfaces such as ACPI; these functions include power management, hot swapping and thermal management. However BIOS limitations (16-bit processor mode, only 1 MiB addressable space, PC AT hardware dependencies, etc.) were seen as clearly unacceptable for the newer computer platforms. Extensible Firmware Interface (EFI) is a specification which replaces the runtime interface of the legacy BIOS. Initially written for the Itanium architecture, EFI is now available for x86 and x86-64 platforms; the specification development is driven by The Unified EFI Forum, an industry Special Interest Group.

Linux has supported EFI via the elilo boot loader. The Open Source community increased their effort to develop a replacement for proprietary BIOSes and their future incarnations with an open sourced counterpart through the coreboot and OpenBIOS/Open Firmware projects. AMD provided product specifications for some chipsets, and Google is sponsoring the project. Motherboard manufacturerTyan offers coreboot next to the standard BIOS with their Opteron line of motherboards. MSI and Gigabyte Technology have followed suit with the MSI K9ND MS-9282 and MSI K9SD MS-9185 resp. the M57SLI-S4 models.

Some BIOSes contain a "SLIC", a digital signature placed inside the BIOS by the manufacturer, for example Dell. This SLIC is inserted in the ACPI table and contains no active code. Computer manufacturers that distribute OEM versions of Microsoft Windows and Microsoft application software can use the SLIC to authenticate licensing to the OEM Windows Installation disk and/or systemrecovery disc containing Windows software. systems having a SLIC can be activated with an OEM Product Key, and they verify an XML formatted OEM certificate against the SLIC in the BIOS as a means of self-activating. If a user performs a fresh install of Windows, they will need to have possession of both the OEM key and the digital certificate for their SLIC in order to bypass activation; in practice this is extremely unlikely and hence the only real way this can be achieved is if the user performs a restore using a pre-customised image provided by the OEM.



The BIOS business
The vast majority of PC motherboard suppliers license a BIOS "core" and toolkit from a commercial third-party, known as an "independent BIOS vendor" or IBV. The motherboard manufacturer then customizes this BIOS to suit its own hardware. For this reason, updated BIOSes are normally obtained directly from the motherboard manufacturer.

Major BIOS vendors include American Megatrends (AMI), Insyde Software, Phoenix Technologies and Byosoft. Former vendors include Award Software which was acquired by Phoenix Technologies in 1998. Phoenix has now phased out the Award Brand name. General Software, which was also acquired by Phoenix in 2007, sold BIOS for Intel processor based embedded systems.