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3,701 | In 1978 National Electrical Manufacturers Association released ICS 3-1978, a standard for programmable microcontrollers, including almost any computer-based controllers, such as single-board computers, numerical, and event-based controllers. |
3,702 | There are several different types of software architecture in common use. |
3,703 | In this design, the software simply has a loop which monitors the input devices. The loop calls subroutines, each of which manages a part of the hardware or software. Hence it is called a simple control loop or programmed input-output. |
3,704 | Some embedded systems are predominantly controlled by interrupts. This means that tasks performed by the system are triggered by different kinds of events; an interrupt could be generated, for example, by a timer at a predefined interval, or by a serial port controller receiving data. |
3,705 | This architecture is used if event handlers need low latency, and the event handlers are short and simple. These systems run a simple task in a main loop also, but this task is not very sensitive to unexpected delays. Sometimes the interrupt handler will add longer tasks to a queue structure. Later, after the interrupt... |
3,706 | Cooperative multitasking is very similar to the simple control loop scheme, except that the loop is hidden in an API. The programmer defines a series of tasks, and each task gets its own environment to run in. When a task is idle, it calls an idle routine which passes control to another task. |
3,707 | The advantages and disadvantages are similar to that of the control loop, except that adding new software is easier, by simply writing a new task, or adding to the queue. |
3,708 | In this type of system, a low-level piece of code switches between tasks or threads based on a timer invoking an interrupt. This is the level at which the system is generally considered to have an operating system kernel. Depending on how much functionality is required, it introduces more or less of the complexities of... |
3,709 | As any code can potentially damage the data of another task programs must be carefully designed and tested, and access to shared data must be controlled by some synchronization strategy such as message queues, semaphores or a non-blocking synchronization scheme. |
3,710 | Because of these complexities, it is common for organizations to use an off-the-shelf RTOS, allowing the application programmers to concentrate on device functionality rather than operating system services. The choice to include an RTOS brings in its own issues, however, as the selection must be made prior to starting ... |
3,711 | The level of complexity in embedded systems is continuously growing as devices are required to manage peripherals and tasks such as serial, USB, TCP/IP, Bluetooth, Wireless LAN, trunk radio, multiple channels, data and voice, enhanced graphics, multiple states, multiple threads, numerous wait states and so on. These tr... |
3,712 | A microkernel allocates memory and switches the CPU to different threads of execution. User-mode processes implement major functions such as file systems, network interfaces, etc. |
3,713 | Exokernels communicate efficiently by normal subroutine calls. The hardware and all the software in the system are available to and extensible by application programmers. |
3,714 | A monolithic kernel is a relatively large kernel with sophisticated capabilities adapted to suit an embedded environment. This gives programmers an environment similar to a desktop operating system like Linux or Microsoft Windows, and is therefore very productive for development. On the downside, it requires considerab... |
3,715 | Common examples of embedded monolithic kernels are embedded Linux, VXWorks and Windows CE. |
3,716 | Despite the increased cost in hardware, this type of embedded system is increasing in popularity, especially on the more powerful embedded devices such as wireless routers and GPS navigation systems. |
3,717 | In addition to the core operating system, many embedded systems have additional upper-layer software components. These components include networking protocol stacks like CAN, TCP/IP, FTP, HTTP, and HTTPS, and storage capabilities like FAT and flash memory management systems. If the embedded device has audio and video c... |
3,718 | In the automotive sector, AUTOSAR is a standard architecture for embedded software. |
3,719 | In computing, BIOS is firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the booting process . The BIOS firmware comes pre-installed on an IBM PC or IBM PC compatible's system board and exists in some UEFI-based systems to maintain compatibility w... |
3,720 | The BIOS in modern PCs initializes and tests the system hardware components , and loads a boot loader from a mass storage device which then initializes a kernel. In the era of DOS, the BIOS provided BIOS interrupt calls for the keyboard, display, storage, and other input/output devices that standardized an interface t... |
3,721 | 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 was stored in a ROM chip on the PC motherboard. In later computer systems, the BIOS contents are stored on flash memory so... |
3,722 | Unified Extensible Firmware Interface is a successor to the legacy PC BIOS, aiming to address its technical limitations. |
3,723 | The term BIOS 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. |
3,724 | 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" and contains the lower-level hardware-specific part of the operating system. Together with the underlying hardware-specific but operating system-independent "... |
3,725 | The BIOS originally proprietary to the IBM PC has been reverse engineered by some companies looking to create compatible systems. |
3,726 | 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 was named "CBIOS" , whereas the "ABIOS" provided new interfaces specifically suited fo... |
3,727 | 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 had not proceeded to the point of successfully initializing a video display adapter. Options on the IBM P... |
3,728 | 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 the keyboard and video display. The modern Wintel machine may store the BIOS configuration settings in flash ROM, perha... |
3,729 | Early Intel processors started at physical address 000FFFF0h. Systems with later processors provide logic to start running the BIOS from the system ROM.
|
3,730 | If the system has just been powered up or the reset button was pressed , the full power-on self-test is run. If Ctrl+Alt+Delete was pressed , a special flag value stored in nonvolatile BIOS memory tested by the BIOS allows bypass of the lengthy POST and memory detection. |
3,731 | The POST identifies, tests and initializes system devices such as the CPU, chipset, RAM, motherboard, video card, keyboard, mouse, hard disk drive, optical disc drive and other hardware, including integrated peripherals. |
3,732 | 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. |
3,733 | After the option ROM scan is completed and all detected ROM modules with valid checksums have been called, or immediately after POST in a BIOS version that does not scan for option ROMs, the BIOS calls INT 19h to start boot processing. Post-boot, programs loaded can also call INT 19h to reboot the system, but they must... |
3,734 | When INT 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. |
3,735 | The BIOS uses the boot devices set in Nonvolatile BIOS memory , or, in the earliest PCs, DIP switches. The BIOS checks each device in order to see if it is bootable by attempting to load the first sector . If the sector cannot be read, the BIOS proceeds to the next device. If the sector is read successfully, some BIOSe... |
3,736 | When a bootable device is found, 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... |
3,737 | A non-disk device such as 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. |
3,738 | 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 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 mak... |
3,739 | The user can select the boot priority implemented by the BIOS. For example, most computers have 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. |
3,740 | 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 second, and typically no other boot devices supported, subject to modi... |
3,741 | On the original IBM PC and XT, if no bootable disk was found, ROM BASIC was started by calling INT 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 . |
3,742 | Later computers would display 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. |
3,743 | 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 is not well defined. Some BIOSes use a CS:IP of 0x0000:0x7C00 while ot... |
3,744 | 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, DMA controller, and other motherboard/chipset hardware as necessary to bring all BIOS services to ready status. DRAM refresh for all... |
3,745 | Peripheral cards such as hard disk drive host bus adapters and video cards have their own firmware, and BIOS extension option ROM may be a part of the expansion card firmware, which provide additional functionality to BIOS. Code in option ROMs runs before the BIOS boots the operating system from mass storage. These ROM... |
3,746 | The motherboard BIOS typically contains code for initializing and bootstrapping integrated display and integrated storage. In addition, plug-in adapter cards such as SCSI, RAID, network interface cards, and video cards often include their own BIOS , complementing or replacing the system BIOS code for the given componen... |
3,747 | An add-in card requires an option ROM if 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 . An additional advantage of ROM on some early PC systems was that ROM was faster than main system RAM. int... |
3,748 | If an expansion ROM wishes to change the way the system boots in a cooperative way, it can use the BIOS Boot Specification 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 ... |
3,749 | 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... |
3,750 | 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 a portion of the "upper memory area" and runs each ROM found, in order. To discover memory-mapped option ROMs, a BIOS impl... |
3,751 | At this point, 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 to provide a user configuration interface, to display diagnostic information, or to do anything else that it requir... |
3,752 | An option ROM should normally return to the BIOS after completing its initialization process. Once 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. |
3,753 | 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 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 I... |
3,754 | The BIOS ROM is customized to the particular manufacturer's hardware, allowing low-level services 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 , but a single, standard, BIOS system call may be invoked to ... |
3,755 | The BIOS provides a small library of basic input/output functions to operate peripherals . When using MS-DOS, BIOS services could be accessed by an application program 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 acc... |
3,756 | 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 programmers observed that using the BIOS ... |
3,757 | In modern PCs running modern operating systems the BIOS interrupt calls is used only during booting and initial loading of operating systems. Before 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 al... |
3,758 | 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 the system has a BIOS, or a CSM-capable UEFI firmware. |
3,759 | 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 i... |
3,760 | Some BIOSes contain a software licensing description table , a digital signature placed inside the BIOS by the original equipment manufacturer , for example Dell. The SLIC is inserted into the ACPI data table and contains no active code. |
3,761 | 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 a SLIC can be preactivated with an OEM product key, and they veri... |
3,762 | 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... |
3,763 | Some older operating systems, for example MS-DOS, rely on the BIOS to carry out most input/output tasks within the PC. |
3,764 | Calling real mode BIOS services directly is inefficient for protected mode operating systems. BIOS interrupt calls are not used by modern multitasking operating systems after they initially load. |
3,765 | In the 1990s, BIOS provided some protected mode interfaces for Microsoft Windows and Unix-like operating systems, such as Advanced Power Management , Plug and Play BIOS, Desktop Management Interface , VESA BIOS Extensions , e820 and MultiProcessor Specification . Starting from the 2000, most BIOSes provide ACPI, SMBIOS... |
3,766 | After operating systems load, the System Management Mode code is still running in SMRAM. Since 2010, BIOS technology is in a transitional process toward UEFI. |
3,767 | Historically, the BIOS in the IBM PC and XT had no built-in user interface. The BIOS versions in earlier PCs were not software configurable; instead, users set the options via DIP switches on the motherboard. Later computers, including all IBM-compatibles with 80286 CPUs, had a battery-backed nonvolatile BIOS memory ... |
3,768 | Early BIOS versions did not have passwords or boot-device selection options. The BIOS was hard-coded to boot from the first floppy drive, or, if that failed, the first hard disk. Access control in early AT-class machines was by a physical keylock switch . Anyone who could switch on the computer could boot it. |
3,769 | Later, 386-class computers started integrating the BIOS setup utility in the ROM itself, alongside the BIOS code; these computers usually boot into the BIOS setup utility if a certain key or key combination is pressed, otherwise the BIOS POST and boot process are executed. |
3,770 | A modern BIOS setup utility has a text user interface or graphical user interface accessed by pressing a certain key on the keyboard when the PC starts. Usually, the key is advertised for short time during the early startup, for example "Press DEL to enter Setup". The actual key depends on specific hardware. Features... |
3,771 | A modern BIOS setup screen often features a PC Health Status or a Hardware Monitoring tab, which directly interfaces with a Hardware Monitor chip of the mainboard. This makes it possible to monitor CPU and chassis temperature, the voltage provided by the power supply unit, as well as monitor and control the speed of th... |
3,772 | Once the system is booted, hardware monitoring and computer fan control is normally done directly by the Hardware Monitor chip itself, which can be a separate chip, interfaced through I²C or SMBus, or come as a part of a Super I/O solution, interfaced through Industry Standard Architecture or Low Pin Count . Some oper... |
3,773 | However, in some circumstances, the BIOS also provides the underlying information about hardware monitoring through ACPI, in which case, the operating system may be using ACPI to perform hardware monitoring. |
3,774 | In modern PCs the BIOS is stored in rewritable EEPROM or NOR flash memory, allowing the contents to be replaced and modified. This rewriting of the contents is sometimes termed flashing. It can be done by a special program, usually provided by the system's manufacturer, or at POST, with a BIOS image in a hard drive or ... |
3,775 | The original IBM PC BIOS was stored on mask-programmed read-only memory chips in sockets on the motherboard. ROMs could be replaced, but not altered, by users. To allow for updates, many compatible computers used re-programmable BIOS memory devices such as EPROM, EEPROM and later flash memory devices. According to R... |
3,776 | 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 wh... |
3,777 | The first flash chips were attached to the ISA bus. Starting in 1998, the BIOS flash moved to the LPC bus, following a new standard implementation known as "firmware hub" . In 2005, the BIOS flash memory moved to the SPI bus. |
3,778 | The size of the BIOS, and the capacity of the ROM, EEPROM, or 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 32 megabytes. For contrast, the original IBM PC BIOS was contained in an 8 KB mask ROM. Some modern motherboards ar... |
3,779 | Another type of firmware chip was found on the IBM PC AT and early compatibles. In the AT, the keyboard interface was controlled by a microcontroller with its own programmable memory. On the IBM AT, that was a 40-pin socketed device, while some manufacturers used an EPROM version of this chip which resembled an EPROM. ... |
3,780 | The BIOS may contain components such as the Memory Reference Code , which is responsible for the memory initialization .: 8 |
3,781 | Modern BIOS includes
Intel Management Engine or AMD Platform Security Processor firmware. |
3,782 | IBM published the entire listings of the BIOS for its original PC, PC XT, PC AT, and other contemporary PC models, in an appendix of the IBM PC Technical Reference Manual for each machine type. The effect of the publication of the BIOS listings is that anyone can see exactly what a definitive BIOS does and how it does ... |
3,783 | In May 1984 Phoenix Software Associates released its first ROM-BIOS, which enabled OEMs to build essentially fully compatible clones without having to reverse-engineer the IBM PC BIOS themselves, as Compaq had done for the Portable, helping fuel the growth in the PC-compatibles industry and sales of non-IBM versions of... |
3,784 | New standards grafted onto the BIOS are usually without complete public documentation or any BIOS listings. As a result, it is not as easy to learn the intimate details about the many non-IBM additions to BIOS as about the core BIOS services. |
3,785 | Many PC motherboard suppliers licensed the BIOS "core" and toolkit from a commercial third party, known as an "independent BIOS vendor" or IBV. The motherboard manufacturer then customized this BIOS to suit its own hardware. For this reason, updated BIOSes are normally obtained directly from the motherboard manufacture... |
3,786 | The open-source community increased their effort to develop a replacement for proprietary BIOSes and their future incarnations with an open-sourced counterparts. Open Firmware was an early attempt to make open source standard for booting firmware. It was initially endorsed by IEEE in its IEEE 1275-1994 standard but was... |
3,787 | EEPROM and Flash memory chips are advantageous because they can be easily updated by the user; it is customary for hardware manufacturers to 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 ... |
3,788 | There are at least five known viruses that attack the BIOS. Two of which were for demonstration purposes. The first one found in the wild was Mebromi, targeting Chinese users. |
3,789 | The first BIOS virus was BIOS Meningitis, which instead of erasing BIOS chips it infected them. BIOS Meningitis was relatively harmless, compared to a virus like CIH. |
3,790 | The second BIOS virus was CIH, also known as the "Chernobyl Virus", which was able to erase flash ROM BIOS content on compatible chipsets. CIH appeared in mid-1998 and became active in April 1999. Often, infected computers could no longer boot, and people had to remove the flash ROM IC from the motherboard and reprogra... |
3,791 | 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 ... |
3,792 | As a result, as of 2008, CIH has become essentially harmless, at worst causing annoyance by infecting executable files and triggering antivirus software. Other BIOS viruses remain possible, however; since most Windows home users without Windows Vista/7's UAC run all applications with administrative privileges, a modern... |
3,793 | The third BIOS virus was a technique presented by John Heasman, principal security consultant for UK-based Next-Generation Security Software. In 2006, at the Black Hat Security Conference, he showed how to elevate privileges and read physical memory, using malicious procedures that replaced normal ACPI functions stored... |
3,794 | The fourth BIOS virus was a technique called "Persistent BIOS infection." It appeared in 2009 at the CanSecWest Security Conference in Vancouver, and at the SyScan Security Conference in Singapore. Researchers Anibal Sacco and Alfredo Ortega, from Core Security Technologies, demonstrated how to insert malicious code in... |
3,795 | Mebromi is a trojan which targets computers with AwardBIOS, Microsoft Windows, and antivirus software from two Chinese companies: Rising Antivirus and Jiangmin KV Antivirus. Mebromi installs a rootkit which infects the Master boot record. |
3,796 | In a December 2013 interview with 60 Minutes, Deborah Plunkett, Information Assurance Director for the US National Security Agency claimed the NSA had uncovered and thwarted a possible BIOS attack by a foreign nation state, targeting the US financial system. The program cited anonymous sources alleging it was a Chinese... |
3,797 | Newer Intel platforms have Intel Boot Guard technology enabled, this technology will check the BIOS digital signature at startup, and the IBG public key is fused into the PCH. End users can't disable this function. |
3,798 | Unified Extensible Firmware Interface supplements the BIOS in many new machines. Initially written for the Intel Itanium architecture, UEFI is now available for x86 and Arm platforms; the specification development is driven by the Unified EFI Forum, an industry Special Interest Group. EFI booting has been supported in... |
3,799 | Other alternatives to the functionality of the "Legacy BIOS" in the x86 world include coreboot and libreboot. |
3,800 | Some servers and workstations use a platform-independent Open Firmware based on the Forth programming language; it is included with Sun's SPARC computers, IBM's RS/6000 line, and other PowerPC systems such as the CHRP motherboards, along with the x86-based OLPC XO-1. |
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