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76-591: The RM Nimbus PC-186 was a 16-bit microcomputer introduced in 1985. It is one of a small number of computers based on the Intel 80186 processor, a version of the Intel 8086 (as used by the IBM PC ) originally intended as a processor for embedded systems. It ran MS-DOS 3.1 but was not IBM PC compatible. The PC-186 could run Windows versions up to and including Windows 3.0 , but only in real mode , as protected mode

152-566: A kernel . In the era of DOS , the BIOS provided BIOS interrupt calls for the keyboard, display, storage, and other input/output (I/O) devices that standardized an interface to application programs and the operating system. More recent operating systems do not use the BIOS interrupt calls after startup. Most BIOS implementations are specifically designed to work with a particular computer or motherboard model, by interfacing with various devices especially system chipset . Originally, BIOS firmware

228-468: A network adapter attempts booting by a procedure that is defined by its option ROM or the equivalent integrated into the motherboard BIOS ROM. As such, option ROMs may also influence or supplant the boot process defined by the motherboard BIOS ROM. With the El Torito optical media boot standard , the optical drive actually emulates a 3.5" high-density floppy disk to the BIOS for boot purposes. Reading

304-567: A serial port , it uses quadrature signalling Keyboard - Earlier models - Proprietary keyboard port, Later models - PS/2 keyboard port Video - 5-pin DIN plug with TTL RGB output compatible with BBC Micro monitor connectors - modified CGA output Parallel - Optional via expansion card - usually with BBC Micro 'user port' alongside- both with ribbon pin connectors Network -BNC connector - Zilog Z-NET, Ethernet expansion cards were available for later models - both allowed network boot Piconet -

380-563: A 20- bit or 24-bit segment or selector-offset address representation to extend the range of addressable memory locations beyond what was possible using only 16-bit addresses. Programs containing more than 2 bytes (65,536 bytes ) of instructions and data therefore required special instructions to switch between their 64-kilobyte segments , increasing the complexity of programming 16-bit applications. BIOS In computing , BIOS ( / ˈ b aɪ ɒ s , - oʊ s / , BY -oss, -⁠ohss ; Basic Input/Output System , also known as

456-533: A BIOS upgrade that fails could brick the motherboard. Unified Extensible Firmware Interface (UEFI) is a successor to the legacy PC BIOS, aiming to address its technical limitations. UEFI firmware may include legacy BIOS compatibility to maintain compatibility with operating systems and option cards that do not support UEFI native operation. Since 2020, all PCs for Intel platforms no longer support Legacy BIOS. The last version of Microsoft Windows to officially support running on PCs which use legacy BIOS firmware

532-602: A ROM chip) that contains a BIOS extension ROM. The motherboard BIOS typically contains code for initializing and bootstrapping integrated display and integrated storage. The initialization process can involve the execution of code related to the device being initialized, for locating the device, verifying the type of device, then establishing base registers, setting pointers , establishing interrupt vector tables, selecting paging modes which are ways for organizing available registers in devices, setting default values for accessing software routines related to interrupts , and setting

608-523: A SLIC can be preactivated 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 (see System Locked Preinstallation , SLP). If a user performs a fresh install of Windows, they will need to have possession of both the OEM key (either SLP or COA) and the digital certificate for their SLIC in order to bypass activation. This can be achieved if

684-556: A Windows icon, that would load a BIOS extension TSR and restart Windows in Real Mode . Various configuration options could be set before launch, and returning to normal IBM-compatible mode was a simple matter of running the same program again with a particular option switch. RM Nimbus PCs were usually connected to local area network supplied by RM. The company's initial network solution was RM Net , comprising RM Nimbus PC-186 workstations and servers. Later an RM Nimbus AX or VX became

760-1018: A customisable menu of programs to execute or a Windows 3.0 desktop, optionally without the 'File' menu in Program Manager . By current standards, network security was primitive. RM Net was superseded in the early 1990s by RM Net LM, a network operating system based on Microsoft LAN Manager . RM Net LM retained support for PC-186 workstations, allowing them to boot to MS-DOS and to start Windows 3.0. 16-bit In computer architecture , 16-bit integers , memory addresses , or other data units are those that are 16 bits (2 octets ) wide. Also, 16-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers , address buses , or data buses of that size. 16-bit microcomputers are microcomputers that use 16-bit microprocessors . A 16-bit register can store 2 different values. The range of integer values that can be stored in 16 bits depends on

836-608: A hard disk that is bootable, but sometimes there is a removable-media drive that has higher boot priority, so the user can cause a removable disk to be booted. In most modern BIOSes, the boot priority order can be configured by the user. In older BIOSes, limited boot priority options are selectable; in the earliest BIOSes, a fixed priority scheme was implemented, with floppy disk drives first, fixed disks (i.e., hard disks) second, and typically no other boot devices supported, subject to modification of these rules by installed option ROMs. The BIOS in an early PC also usually would only boot from

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912-444: A hard drive, as well as a 3½" floppy drive. By default they were equipped with a Zilog Z-Net interface card, but a second Ethernet card could be added alongside to allow both network interfaces to be used simultaneously, however, the two network interfaces were not able to be bridged. Expansion cards could be added to standard 8-bit and 16-bit ISA sockets, which were both on the motherboard, and on an attached expansion board which

988-561: A message like "No bootable disk found"; some would prompt for a disk to be inserted and a key to be pressed to retry the boot process. A modern BIOS may display nothing or may automatically enter the BIOS configuration utility when the boot process fails. The environment for the boot program is very simple: the CPU is in real mode and the general-purpose and segment registers are undefined, except SS, SP, CS, and DL. CS:IP always points to physical address 0x07C00 . What values CS and IP actually have

1064-547: A network device or a SCSI adapter) 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

1140-422: A portion of the " upper memory area " (the part of the x86 real-mode address space at and above address 0xA0000) and runs each ROM found, in order. To discover memory-mapped option ROMs, a BIOS implementation scans the real-mode address space from 0x0C0000 to 0x0F0000 on 2  KB (2,048 bytes) boundaries, looking for a two-byte ROM signature : 0x55 followed by 0xAA. In a valid expansion ROM, this signature

1216-487: A proprietary serial interface for connecting peripherals Power - Standard IEC connector in and out for monitor supply The RM Nimbus AX and VX models were launched in 1986 and used the 80286 (later the 80386 ) processor. They were fully IBM-compatible, as were all subsequent RM computers. The AX and VX were offered for use as a network file server or as a high-end workstation. They employed either EGA or VGA graphics cards, and were equipped with an ESDI interface for

1292-464: A reserved block of system RAM at addresses 0x00400–0x004FF with various parameters initialized during the POST. All memory at and above address 0x00500 can be used by the boot program; it may even overwrite itself. 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

1368-717: A similar fashion, later 68000-family members, starting with the Motorola 68020 , had 32-bit ALUs. One may also see references to systems being, or not being, 16-bit based on some other measure. One common one is when the address space is not the same size of bits as the internal registers. Most 8-bit CPUs of the 1970s fall into this category; the MOS 6502 , Intel 8080 , Zilog Z80 and most others had 16-bit address space which provided 64 KB of address space. This also meant address manipulation required two instruction cycles. For this reason, most processors had special 8-bit addressing modes,

1444-503: A simple boot loader in its ROM.) Versions of MS-DOS , PC DOS or DR-DOS contain a file called variously " IO.SYS ", " IBMBIO.COM ", "IBMBIO.SYS", or "DRBIOS.SYS"; this file is known as the "DOS BIOS" (also known as the "DOS I/O System") and contains the lower-level hardware-specific part of the operating system. Together with the underlying hardware-specific but operating system-independent "System BIOS", which resides in ROM , it represents

1520-621: A software licensing description table (SLIC), a digital signature placed inside the BIOS by the original equipment manufacturer (OEM), for example Dell . The SLIC is inserted into the ACPI data 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 system recovery disc containing Windows software. Systems with

1596-454: 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

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1672-476: Is Windows 10 as Windows 11 requires a UEFI-compliant system (except for IoT Enterprise editions of Windows 11 since version 24H2 ). The term BIOS (Basic Input/Output System) was created by Gary Kildall and first appeared in the CP/M operating system in 1975, describing the machine-specific part of CP/M loaded during boot time that interfaces directly with the hardware . (A CP/M machine usually has only

1748-406: Is bootable by attempting to load the first sector ( boot sector ). If the sector cannot be read, the BIOS proceeds to the next device. If the sector is read successfully, some BIOSes will also check for the boot sector signature 0x55 0xAA in the last two bytes of the sector (which is 512 bytes long), before accepting a boot sector and considering the device bootable. When a bootable device is found,

1824-452: Is followed by a single byte indicating the number of 512-byte blocks the expansion ROM occupies in real memory, and the next byte is the option ROM's entry point (also known as its "entry offset"). If the ROM has a valid checksum, the BIOS transfers control to the entry address, which in a normal BIOS extension ROM should be the beginning of the extension's initialization routine. At this point,

1900-556: Is not well defined. Some BIOSes use a CS:IP of 0x0000:0x7C00 while others may use 0x07C0:0x0000 . Because boot programs are always loaded at this fixed address, there is no need for a boot program to be relocatable. DL may contain the drive number, as used with interrupt 13h , of the boot device. SS:SP points to a valid stack that is presumably large enough to support hardware interrupts, but otherwise SS and SP are undefined. (A stack must be already set up in order for interrupts to be serviced, and interrupts must be enabled in order for

1976-471: Is performed each time the system is powered up. Without reprogrammable microcode, an expensive processor swap would be required; for example, the Pentium FDIV bug became an expensive fiasco for Intel as it required a product recall because the original Pentium processor's defective microcode could not be reprogrammed. Operating systems can update main processor microcode also. Some BIOSes contain

2052-541: Is rebooting. When interrupt 19h is called, the BIOS attempts to locate boot loader software on a "boot device", such as a hard disk , a floppy disk , CD , or DVD . It loads and executes the first boot software it finds, giving it control of the PC. The BIOS uses the boot devices set in Nonvolatile BIOS memory ( CMOS ), or, in the earliest PCs, DIP switches . The BIOS checks each device in order to see if it

2128-488: Is running. The interrupt vectors corresponding to the BIOS interrupts have been set to point at the appropriate entry points in the BIOS, hardware interrupt vectors for devices initialized by the BIOS have been set to point to the BIOS-provided ISRs, and some other interrupts, including ones that BIOS generates for programs to hook, have been set to a default dummy ISR that immediately returns. The BIOS maintains

2204-416: Is sometimes called 16-bit because of the way it handles basic arithmetic. The instruction set was based on 32-bit numbers and the internal registers were 32 bits wide, so by common definitions, the 68000 is a 32-bit design. Internally, 32-bit arithmetic is performed using two 16-bit operations, and this leads to some descriptions of the system as 16-bit, or "16/32". Such solutions have a long history in

2280-663: Is unique among PCs in having two ROM cartridge slots on the front. Cartridges in these slots map into the same region of the upper memory area used for option ROMs, and the cartridges can contain option ROM modules that the BIOS would recognize. The cartridges can also contain other types of ROM modules, such as BASIC programs, that are handled differently. One PCjr cartridge can contain several ROM modules of different types, possibly stored together in one ROM chip. The 8086 and 8088 start at physical address FFFF0h. The 80286 starts at physical address FFFFF0h. The 80386 and later x86 processors start at physical address FFFFFFF0h. When

2356-451: The 386SX , which is a 32-bit processor with 32-bit ALU and internal 32-bit data paths with a 16-bit external bus and 24-bit addressing of the processor it replaced. In the context of IBM PC compatible and Wintel platforms, a 16-bit application is any software written for MS-DOS , OS/2 1.x or early versions of Microsoft Windows which originally ran on the 16-bit Intel 8088 and Intel 80286 microprocessors . Such applications used

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2432-611: The CPU , chipset , RAM , motherboard , video card , keyboard , mouse , hard disk drive , optical disc drive and other hardware , including integrated peripherals . Early IBM PCs had a routine in the POST that would download a program into RAM through the keyboard port and run it. This feature was intended for factory test or diagnostic purposes. After the motherboard BIOS completes its POST, most BIOS versions search for option ROM modules, also called BIOS extension ROMs, and execute them. The motherboard BIOS scans for extension ROMs in

2508-587: The Intel 80286 , the WDC 65C816 , and the Zilog Z8000 . The Intel 8088 was binary compatible with the Intel 8086, and was 16-bit in that its registers were 16 bits wide, and arithmetic instructions could operate on 16-bit quantities, even though its external bus was 8 bits wide. 16-bit processors have been almost entirely supplanted in the personal computer industry, and are used less than 32-bit (or 8-bit) CPUs in embedded applications. The Motorola 68000

2584-526: The Nimbus name, although it was still used late enough to appear on some early (and still ISA-based) 486 models shipped in slightly taller (2 x 5.25" bay) cases. By this point, RM's computers were essentially ordinary IBM clones being sold specifically to the education market, with standard processors and buses, operating systems and software, as well as the normal ports (5-pin AT keyboard , 9-pin serial - including

2660-558: The System BIOS , ROM BIOS , BIOS ROM or PC BIOS ) is firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the booting process (power-on startup). The firmware comes pre-installed on the computer's motherboard . The name originates from the Basic Input/Output System used in the CP/M operating system in 1975. The BIOS firmware

2736-513: The integer representation used. With the two most common representations, the range is 0 through 65,535 (2 − 1) for representation as an ( unsigned ) binary number , and −32,768 (−1 × 2 ) through 32,767 (2 − 1) for representation as two's complement . Since 2 is 65,536, a processor with 16-bit memory addresses can directly access 64 KB (65,536 bytes) of byte-addressable memory. If a system uses segmentation with 16-bit segment offsets, more can be accessed. The MIT Whirlwind ( c. 1951)

2812-520: The zero page , improving speed. This sort of difference between internal register size and external address size remained in the 1980s, although often reversed, as memory costs of the era made a machine with 32-bit addressing, 2 or 4 GB, a practical impossibility. For example, the 68000 exposed only 24 bits of addressing on the DIP , limiting it to a still huge (for the era) 16 MB. A similar analysis applies to Intel's 80286 CPU replacement, called

2888-423: The "first sector" of a CD-ROM or DVD-ROM is not a simply defined operation like it is on a floppy disk or a hard disk. Furthermore, the complexity of the medium makes it difficult to write a useful boot program in one sector. The bootable virtual floppy disk can contain software that provides access to the optical medium in its native format. If an expansion ROM wishes to change the way the system boots (such as from

2964-627: The 1960s, especially on minicomputer systems. Early 16-bit computers ( c. 1965–70) include the IBM 1130 , the HP 2100 , the Data General Nova , and the DEC PDP-11 . Early 16-bit microprocessors , often modeled on one of the mini platforms, began to appear in the 1970s. Examples ( c. 1973–76) include the five-chip National Semiconductor IMP-16 (1973), the two-chip NEC μCOM-16 (1974),

3040-430: The 1980s under MS-DOS , when programmers observed that using the BIOS video services for graphics display were very slow. To increase the speed of screen output, many programs bypassed the BIOS and programmed the video display hardware directly. Other graphics programmers, particularly but not exclusively in the demoscene , observed that there were technical capabilities of the PC display adapters that were not supported by

3116-424: The BIOS after completing its initialization process. Once (and if) an option ROM returns, the BIOS continues searching for more option ROMs, calling each as it is found, until the entire option ROM area in the memory space has been scanned. It is possible that an option ROM will not return to BIOS, pre-empting the BIOS's boot sequence altogether. After the POST completes and, in a BIOS that supports option ROMs, after

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3192-601: The BIOS to carry out most input/output tasks within the PC. Calling real mode BIOS services directly is inefficient for protected mode (and long mode ) operating systems. BIOS interrupt calls are not used by modern multitasking operating systems after they initially load. In the 1990s, BIOS provided some protected mode interfaces for Microsoft Windows and Unix-like operating systems, such as Advanced Power Management (APM), Plug and Play BIOS , Desktop Management Interface (DMI), VESA BIOS Extensions (VBE), e820 and MultiProcessor Specification (MPS). Starting from

3268-408: The BIOS transfers control to the loaded sector. The BIOS does not interpret the contents of the boot sector other than to possibly check for the boot sector signature in the last two bytes. Interpretation of data structures like partition tables and BIOS Parameter Blocks is done by the boot program in the boot sector itself or by other programs loaded through the boot process. A non-disk device such as

3344-630: The BIOS. Code in option ROMs runs before the BIOS boots the operating system from mass storage . These ROMs typically test and initialize hardware, add new BIOS services, or replace existing BIOS services with their own services. For example, a SCSI controller usually has a BIOS extension ROM that adds support for hard drives connected through that controller. An extension ROM could in principle contain operating system, or it could implement an entirely different boot process such as network booting . Operation of an IBM-compatible computer system can be completely changed by removing or inserting an adapter card (or

3420-665: The IBM BIOS and could not be taken advantage of without circumventing it. Since the AT-compatible BIOS ran in Intel real mode , operating systems that ran in protected mode on 286 and later processors required hardware device drivers compatible with protected mode operation to replace BIOS services. In modern PCs running modern operating systems (such as Windows and Linux ) the BIOS interrupt calls are used only during booting and initial loading of operating systems. Before

3496-500: The analogue to the " CP/M BIOS ". The BIOS originally proprietary to the IBM PC has been reverse engineered by some companies (such as Phoenix Technologies ) looking to create compatible systems. With the introduction of PS/2 machines, IBM divided the System BIOS into real- and protected-mode portions. The real-mode portion was meant to provide backward compatibility with existing operating systems such as DOS, and therefore

3572-510: 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. The user can select the boot priority implemented by the BIOS. For example, most computers have

3648-459: The card is not supported by the motherboard 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 boot process). 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

3724-503: The computer field, with various designs performing math even one bit at a time, known as "serial arithmetic", while most designs by the 1970s processed at least a few bits at a time. A common example is the Data General Nova, which was a 16-bit design that performed 16-bit math as a series of four 4-bit operations. 4-bits was the word size of a widely available single-chip ALU and thus allowed for inexpensive implementation. Using

3800-492: The computer, and if it was lost the system settings could not be changed. The same applied in general to computers with an EISA bus, for which the configuration program was called an EISA Configuration Utility (ECU). A modern Wintel -compatible computer provides a setup routine essentially unchanged in nature from the ROM-resident BIOS setup utilities of the late 1990s; the user can configure hardware options using

3876-525: The definition being applied to the 68000, the Nova would be a 4-bit computer, or 4/16. Not long after the introduction of the Nova, a second version was introduced, the SuperNova, which included four of the 4-bit ALUs running in parallel to perform math 16 bits at a time and therefore offer higher performance. This was invisible to the user and the programs, which always used 16-bit instructions and data. In

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3952-440: The device's configuration using default values. In addition, plug-in adapter cards such as SCSI , RAID , network interface cards , and video cards often include their own BIOS (e.g. Video BIOS ), complementing or replacing the system BIOS code for the given component. Even devices built into the motherboard can behave in this way; their option ROMs can be a part of the motherboard BIOS. An add-in card requires an option ROM if

4028-485: The expansion ROMs have finished executing and registering themselves with the BBS API. Also, if an expansion ROM wishes to change the way the system boots unilaterally, it can simply hook interrupt 19h or other interrupts normally called from interrupt 19h, such as interrupt 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

4104-416: The extension ROM code takes over, typically testing and initializing the hardware it controls and registering interrupt vectors for use by post-boot applications. It may use BIOS services (including those provided by previously initialized option ROMs) to provide a user configuration interface, to display diagnostic information, or to do anything else that it requires. An option ROM should normally return to

4180-465: The first floppy disk drive or the first hard disk drive, even if there were two drives installed. On the original IBM PC and XT, if no bootable disk was found, the BIOS would try to start ROM BASIC with the interrupt call to interrupt 18h . Since few programs used BASIC in ROM, clone PC makers left it out; then a computer that failed to boot from a disk would display "No ROM BASIC" and halt (in response to interrupt 18h). Later computers would display

4256-403: The keyboard and video display. The modern Wintel machine may store the BIOS configuration settings in flash ROM, perhaps the same flash ROM that holds the BIOS itself. Peripheral cards such as hard disk drive host bus adapters and video cards have their own firmware, and BIOS extension option ROM code may be a part of the expansion card firmware; that code provides additional capabilities in

4332-654: 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 interrupt 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

4408-508: The mouse, 15-pin HD-sub VGA - although some 386 models used the less common 9-pin variant, etc), and the previous non-standard holdovers from the 380Z days long since abandoned. Despite moving to a standard IBM-compatible architecture from the X series onwards, RM somewhat unusually maintained backwards compatibility with software written for their original Nimbus model by way of a "PC186" program that could be launched from MS-DOS or via

4484-527: The operating system's first graphical screen is displayed, input and output are typically handled through BIOS. A boot menu such as the textual menu of Windows, which allows users to choose an operating system to boot, to boot into the safe mode , or to use the last known good configuration, is displayed through BIOS and receives keyboard input through BIOS. Many modern PCs can still boot and run legacy operating systems such as MS-DOS or DR-DOS that rely heavily on BIOS for their console and disk I/O, providing that

4560-425: The option ROM scan is completed and all detected ROM modules with valid checksums have been called, the BIOS calls interrupt 19h to start boot processing. Post-boot, programs loaded can also call interrupt 19h to reboot the system, but they must be careful to disable interrupts and other asynchronous hardware processes that may interfere with the BIOS rebooting process, or else the system may hang or crash while it

4636-548: The point of successfully initializing a video display adapter. Options on the IBM PC and XT were set by switches and jumpers on the main board and on expansion cards . Starting around the mid-1990s, it became typical for the BIOS ROM to include a "BIOS configuration utility" (BCU ) or "BIOS setup utility", accessed at system power-up by a particular key sequence. This program allowed the user to set system configuration options, of

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4712-621: The reverse of this, and BIOS ROM code is usually copied ("shadowed") into RAM so it will run faster.) Option ROMs normally reside on adapter cards. However, the original PC, and perhaps also the PC XT, have a spare ROM socket on the motherboard (the "system board" in IBM's terms) into which an option ROM can be inserted, and the four ROMs that contain the BASIC interpreter can also be removed and replaced with custom ROMs which can be option ROMs. The IBM PCjr

4788-672: The stack set up by BIOS is unknown and its location is likewise variable; although the boot program can investigate the default stack by examining SS:SP, it is easier and shorter to just unconditionally set up a new stack. At boot time, all BIOS services are available, and the memory below address 0x00400 contains the interrupt vector table . BIOS POST has initialized the system timers, interrupt controller(s), DMA controller(s), and other motherboard/chipset hardware as necessary to bring all BIOS services to ready status. DRAM refresh for all system DRAM in conventional memory and extended memory, but not necessarily expanded memory, has been set up and

4864-537: The system has a BIOS, or a CSM-capable UEFI firmware. Intel processors have reprogrammable microcode since the P6 microarchitecture. AMD processors have reprogrammable microcode since the K7 microarchitecture. The BIOS contain patches to the processor microcode that fix errors in the initial processor microcode; microcode is loaded into processor's SRAM so reprogramming is not persistent, thus loading of microcode updates

4940-479: The system is initialized, the first instruction of the BIOS appears at that address. If the system has just been powered up or the reset button was pressed (" cold boot "), the full power-on self-test (POST) is run. If Ctrl+Alt+Delete was pressed (" warm boot "), a special flag value stored in nonvolatile BIOS memory (" CMOS ") tested by the BIOS allows bypass of the lengthy POST and memory detection. The POST identifies, tests and initializes system devices such as

5016-405: The system timer-tick interrupt, which BIOS always uses at least to maintain the time-of-day count and which it initializes during POST, to be active and for the keyboard to work. The keyboard works even if the BIOS keyboard service is not called; keystrokes are received and placed in the 15-character type-ahead buffer maintained by BIOS.) The boot program must set up its own stack, because the size of

5092-519: The three-chip Western Digital MCP-1600 (1975), and the five-chip Toshiba T-3412 (1976). Early single-chip 16-bit microprocessors ( c. 1975–76) include the Panafacom MN1610 (1975), National Semiconductor PACE (1975), General Instrument CP1600 (1975), Texas Instruments TMS9900 (1976), Ferranti F100-L , and the HP BPC . Other notable 16-bit processors include the Intel 8086 ,

5168-461: The type formerly set using DIP switches , through an interactive menu system controlled through the keyboard. In the interim period, IBM-compatible PCs‍—‌including the IBM AT ‍—‌held configuration settings in battery-backed RAM and used a bootable configuration program on floppy disk, not in the ROM, to set the configuration options contained in this memory. The floppy disk was supplied with

5244-780: The user performs a restore using a pre-customised image provided by the OEM. Power users can copy the necessary certificate files from the OEM image, decode the SLP product key, then perform SLP activation manually. Some BIOS implementations allow overclocking , an action in which the CPU is adjusted to a higher clock rate than its manufacturer rating for guaranteed capability. Overclocking may, however, seriously compromise system reliability in insufficiently cooled computers and generally shorten component lifespan. Overclocking, when incorrectly performed, may also cause components to overheat so quickly that they mechanically destroy themselves. Some older operating systems , for example MS-DOS , rely on

5320-463: The usual choice of fileserver. PC-186 workstations could be designated as print servers , allowing shared access to printers from all workstations. The network used Microsoft MS-Net server and client software, Zilog Z-Net network interface cards, coaxial cable and BNC connectors . It allowed up to 127 workstations to be connected and booted directly from the network server . Network users could be members of user groups, with each group receiving

5396-433: Was named "CBIOS" (for "Compatibility BIOS"), whereas the "ABIOS" (for "Advanced BIOS") provided new interfaces specifically suited for multitasking operating systems such as OS/2 . The BIOS of the original IBM PC and XT had no interactive user interface. Error codes or messages were displayed on the screen, or coded series of sounds were generated to signal errors when the power-on self-test (POST) had not proceeded to

5472-602: Was only available on 286 or higher processors. Most PC-186 systems were used as workstations within a local area network and were supplied without a hard disk. The operating system was started from a floppy disk or via a remote boot ROM on its network interface card, connecting to the LAN's fileserver . Stand-alone workstations were rarer but available with either twin floppy drives or a 20Mbyte hard drive and single floppy drive. Mouse - 9-pin D-Sub connector , sometimes confused as

5548-432: Was originally proprietary to the IBM PC ; it was reverse engineered by some companies (such as Phoenix Technologies ) looking to create compatible systems. The interface of that original system serves as a de facto standard . The BIOS in older PCs initializes and tests the system hardware components ( power-on self-test or POST for short), and loads a boot loader from a mass storage device which then initializes

5624-443: Was quite possibly the first-ever 16-bit computer. It was an unusual word size for the era; most systems used six-bit character code and used a word length of some multiple of 6-bits. This changed with the effort to introduce ASCII , which used a 7-bit code and naturally led to the use of an 8-bit multiple which could store a single ASCII character or two binary coded decimal digits. The 16-bit word length thus became more common in

5700-406: Was stored in a ROM chip on the PC motherboard. In later computer systems, the BIOS contents are stored on flash memory so it can be rewritten without removing the chip from the motherboard. This allows easy, end-user updates to the BIOS firmware so new features can be added or bugs can be fixed, but it also creates a possibility for the computer to become infected with BIOS rootkits . Furthermore,

5776-646: Was supplied as standard. RM released PCs based on Intel 286 and 386 processors under the RM Nimbus name. The PC-286 and early PC-386 versions were termed the M Series due to the MCA bus used, and had a similar case design to that used by later models of the PC-186. Later RM PCs using the 386 processor used an ISA bus and were shipped in a particularly ("S" for) slimline desktop case with only two 3.5" drive bays. The processor typically ran at 16 or 25MHz. Later models dropped

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