113-525: [REDACTED] Look up šlic in Wiktionary, the free dictionary. SLIC may refer to: Software licensing description table , in a computer BIOS Sri Lanka Insurance Corporation , an insurance provider State Life Insurance Corporation of Pakistan Subaxial Injury Classification, a severity score for cervical spine trauma Subscriber line interface card , an electronic circuit Topics referred to by
226-474: 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 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
339-463: 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
452-636: A 1024 GB flash chip, with eight stacked 96-layer V-NAND chips and with QLC technology. Flash memory stores information in an array of memory cells made from floating-gate transistors . In single-level cell (SLC) devices, each cell stores only one bit of information. Multi-level cell (MLC) devices, including triple-level cell (TLC) devices, can store more than one bit per cell. The floating gate may be conductive (typically polysilicon in most kinds of flash memory) or non-conductive (as in SONOS flash memory). In flash memory, each memory cell resembles
565-489: A 16 GB flash memory chip that was manufactured with 24 stacked NAND flash chips using a wafer bonding process. Toshiba also used an eight-layer 3D IC for their 32 GB THGBM flash chip in 2008. In 2010, Toshiba used a 16-layer 3D IC for their 128 GB THGBM2 flash chip, which was manufactured with 16 stacked 8 GB chips. In the 2010s, 3D ICs came into widespread commercial use for NAND flash memory in mobile devices . In 2016, Micron and Intel introduced
678-433: A 64 MB NOR flash memory chip. In 2009, Toshiba and SanDisk introduced NAND flash chips with QLC technology storing 4 bits per cell and holding a capacity of 64 Gbit. Samsung Electronics introduced triple-level cell (TLC) technology storing 3-bits per cell, and began mass-producing NAND chips with TLC technology in 2010. Charge trap flash (CTF) technology replaces the polysilicon floating gate, which
791-602: 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
904-516: 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
1017-548: A certain number of faults (NOR flash, as is used for a BIOS ROM, is expected to be fault-free). Manufacturers try to maximize the amount of usable storage by shrinking the size of the transistors or cells, however the industry can avoid this and achieve higher storage densities per die by using 3D NAND, which stacks cells on top of each other. NAND flash cells are read by analysing their response to various voltages. NAND flash uses tunnel injection for writing and tunnel release for erasing. NAND flash memory forms
1130-517: A charge-trapping mechanism for NOR flash memory cells. CTF was later commercialized by AMD and Fujitsu in 2002. 3D V-NAND (vertical NAND) technology stacks NAND flash memory cells vertically within a chip using 3D charge trap flash (CTP) technology. 3D V-NAND technology was first announced by Toshiba in 2007, and the first device, with 24 layers, was first commercialized by Samsung Electronics in 2013. 3D integrated circuit (3D IC) technology stacks integrated circuit (IC) chips vertically into
1243-608: 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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#17328523696611356-558: 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
1469-425: A more typical 10,000 or 100,000 erase cycles, up to 1,000,000 erase cycles. NOR-based flash was the basis of early flash-based removable media; CompactFlash was originally based on it, though later cards moved to less expensive NAND flash. NAND flash has reduced erase and write times, and requires less chip area per cell, thus allowing greater storage density and lower cost per bit than NOR flash. However,
1582-532: 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
1695-518: A planar charge trap cell into a cylindrical form. As of 2020, 3D NAND flash memories by Micron and Intel instead use floating gates, however, Micron 128 layer and above 3D NAND memories use a conventional charge trap structure, due to the dissolution of the partnership between Micron and Intel. Charge trap 3D NAND flash is thinner than floating gate 3D NAND. In floating gate 3D NAND, the memory cells are completely separated from one another, whereas in charge trap 3D NAND, vertical groups of memory cells share
1808-422: 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
1921-460: 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
2034-463: A separate flash memory controller chip. The NAND type is found mainly in memory cards , USB flash drives , solid-state drives (those produced since 2009), feature phones , smartphones , and similar products, for general storage and transfer of data. NAND or NOR flash memory is also often used to store configuration data in digital products, a task previously made possible by EEPROM or battery-powered static RAM . A key disadvantage of flash memory
2147-421: A separate die inside the package. The origins of flash memory can be traced back to the development of the floating-gate MOSFET (FGMOS) , also known as the floating-gate transistor. The original MOSFET was invented at Bell Labs between 1955 and 1960, after Frosch and Derick discovered surface passivation and used their discovery to create the first planar transistors. Dawon Kahng went on to develop
2260-500: 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
2373-485: A single 3D IC chip package. Toshiba introduced 3D IC technology to NAND flash memory in April 2007, when they debuted a 16 GB eMMC compliant (product number THGAM0G7D8DBAI6, often abbreviated THGAM on consumer websites) embedded NAND flash memory chip, which was manufactured with eight stacked 2 GB NAND flash chips. In September 2007, Hynix Semiconductor (now SK Hynix ) introduced 24-layer 3D IC technology, with
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#17328523696612486-424: A single memory product. A single-level NOR flash cell in its default state is logically equivalent to a binary "1" value, because current will flow through the channel under application of an appropriate voltage to the control gate, so that the bitline voltage is pulled down. A NOR flash cell can be programmed, or set to a binary "0" value, by the following procedure: To erase a NOR flash cell (resetting it to
2599-409: A single supply voltage and produce the high voltages that are required using on-chip charge pumps . Over half the energy used by a 1.8 V-NAND flash chip is lost in the charge pump itself. Since boost converters are inherently more efficient than charge pumps, researchers developing low-power SSDs have proposed returning to the dual Vcc/Vpp supply voltages used on all early flash chips, driving
2712-607: 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
2825-485: A standard metal–oxide–semiconductor field-effect transistor (MOSFET) except that the transistor has two gates instead of one. The cells can be seen as an electrical switch in which current flows between two terminals (source and drain) and is controlled by a floating gate (FG) and a control gate (CG). The CG is similar to the gate in other MOS transistors, but below this, there is the FG insulated all around by an oxide layer. The FG
2938-454: 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
3051-472: A technology known as CMOS Under the Array/CMOS Under Array (CUA), Core over Periphery (COP), Periphery Under Cell (PUA), or Xtacking, in which the control circuitry for the flash memory is placed under or above the flash memory cell array. This has allowed for an increase in the number of planes or sections a flash memory chip has, increasing from 2 planes to 4, without increasing the area dedicated to
3164-838: A time. NAND flash also uses floating-gate transistors , but they are connected in a way that resembles a NAND gate : several transistors are connected in series, and the bit line is pulled low only if all the word lines are pulled high (above the transistors' V T ). These groups are then connected via some additional transistors to a NOR-style bit line array in the same way that single transistors are linked in NOR ;flash. Compared to NOR flash, replacing single transistors with serial-linked groups adds an extra level of addressing. Whereas NOR flash might address memory by page then word, NAND flash might address it by page, word and bit. Bit-level addressing suits bit-serial applications (such as hard disk emulation), which access only one bit at
3277-453: A time. Execute-in-place applications, on the other hand, require every bit in a word to be accessed simultaneously. This requires word-level addressing. In any case, both bit and word addressing modes are possible with either NOR or NAND flash. To read data, first the desired group is selected (in the same way that a single transistor is selected from a NOR array). Next, most of the word lines are pulled up above V T2 , while one of them
3390-506: A type of flash memory with a charge trap method. In 1998, Boaz Eitan of Saifun Semiconductors (later acquired by Spansion ) patented a flash memory technology named NROM that took advantage of a charge trapping layer to replace the conventional floating gate used in conventional flash memory designs. In 2000, an Advanced Micro Devices (AMD) research team led by Richard M. Fastow, Egyptian engineer Khaled Z. Ahmed and Jordanian engineer Sameer Haddad (who later joined Spansion) demonstrated
3503-447: A variation, the floating-gate MOSFET, with Taiwanese-American engineer Simon Min Sze at Bell Labs in 1967. They proposed that it could be used as floating-gate memory cells for storing a form of programmable read-only memory ( PROM ) that is both non-volatile and re-programmable. Early types of floating-gate memory included EPROM (erasable PROM) and EEPROM (electrically erasable PROM) in
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3616-472: 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
3729-444: Is an electrically insulating tunnel oxide layer between the floating gate and the silicon, so the gate "floats" above the silicon. The oxide keeps the electrons confined to the floating gate. Degradation or wear (and the limited endurance of floating gate Flash memory) occurs due to the extremely high electric field (10 million volts per centimeter) experienced by the oxide. Such high voltage densities can break atomic bonds over time in
3842-406: 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,
3955-523: Is different from Wikidata All article disambiguation pages All disambiguation pages Software licensing description table In computing , BIOS ( / ˈ b aɪ ɒ s , - oʊ s / , BY -oss, -ohss ; Basic Input/Output System , also known as 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
4068-449: 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,
4181-518: Is interposed between the CG and the MOSFET channel. Because the FG is electrically isolated by its insulating layer, electrons placed on it are trapped. When the FG is charged with electrons, this charge screens the electric field from the CG, thus, increasing the threshold voltage (V T ) of the cell. This means that the V T of the cell can be changed between the uncharged FG threshold voltage (V T1 ) and
4294-556: 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
4407-553: Is often employed in scenarios where cost-effective, high-capacity storage is crucial, such as in USB drives, memory cards, and solid-state drives ( SSDs ). The primary differentiator lies in their use cases and internal structures. NOR flash is optimal for applications requiring quick access to individual bytes, like in embedded systems for program execution. NAND flash, on the other hand, shines in scenarios demanding cost-effective, high-capacity storage with sequential data access. Flash memory
4520-465: 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
4633-625: Is programmed in blocks while EEPROM is programmed in bytes. According to Toshiba, the name "flash" was suggested by Masuoka's colleague, Shōji Ariizumi, because the erasure process of the memory contents reminded him of the flash of a camera . Masuoka and colleagues presented the invention of NOR flash in 1984, and then NAND flash at the IEEE 1987 International Electron Devices Meeting (IEDM) held in San Francisco. Toshiba commercially launched NAND flash memory in 1987. Intel Corporation introduced
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4746-422: Is pulled up to V I . The series group will conduct (and pull the bit line low) if the selected bit has not been programmed. Despite the additional transistors, the reduction in ground wires and bit lines allows a denser layout and greater storage capacity per chip. (The ground wires and bit lines are actually much wider than the lines in the diagrams.) In addition, NAND flash is typically permitted to contain
4859-530: 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
4972-480: 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
5085-484: Is sandwiched between a blocking gate oxide above and a tunneling oxide below it, with an electrically insulating silicon nitride layer; the silicon nitride layer traps electrons. In theory, CTF is less prone to electron leakage, providing improved data retention. Because CTF replaces the polysilicon with an electrically insulating nitride, it allows for smaller cells and higher endurance (lower degradation or wear). However, electrons can become trapped and accumulate in
5198-510: Is that it can endure only a relatively small number of write cycles in a specific block. NOR flash is known for its direct random access capabilities, making it apt for executing code directly. Its architecture allows for individual byte access, facilitating faster read speeds compared to NAND flash. NAND flash memory operates with a different architecture, relying on a serial access approach. This makes NAND suitable for high-density data storage but less efficient for random access tasks. NAND flash
5311-513: Is thus highly suitable for use in mass-storage devices, such as memory cards and solid-state drives (SSD). For example, SSDs store data using multiple NAND flash memory chips. The first NAND-based removable memory card format was SmartMedia , released in 1995. Many others followed, including MultiMediaCard , Secure Digital , Memory Stick , and xD-Picture Card . A new generation of memory card formats, including RS-MMC , miniSD and microSD , feature extremely small form factors. For example,
5424-663: 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
5537-485: Is used in computers , PDAs , digital audio players , digital cameras , mobile phones , synthesizers , video games , scientific instrumentation , industrial robotics , and medical electronics . Flash memory has a fast read access time but it is not as fast as static RAM or ROM. In portable devices, it is preferred to use flash memory because of its mechanical shock resistance since mechanical drives are more prone to mechanical damage. Because erase cycles are slow,
5650-608: 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
5763-544: The NOR and NAND logic gates . Both use the same cell design, consisting of floating-gate MOSFETs . They differ at the circuit level depending on whether the state of the bit line or word lines is pulled high or low: in NAND flash, the relationship between the bit line and the word lines resembles a NAND gate; in NOR flash, it resembles a NOR gate. Flash memory, a type of floating-gate memory,
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#17328523696615876-559: 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 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
5989-498: The "1" state), a large voltage of the opposite polarity is applied between the CG and source terminal, pulling the electrons off the FG through Fowler–Nordheim tunneling (FN tunneling). This is known as Negative gate source source erase. Newer NOR memories can erase using negative gate channel erase, which biases the wordline on a NOR memory cell block and the P-well of the memory cell block to allow FN tunneling to be carried out, erasing
6102-423: 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
6215-712: The 1970s. However, early floating-gate memory required engineers to build a memory cell for each bit of data, which proved to be cumbersome, slow, and expensive, restricting floating-gate memory to niche applications in the 1970s, such as military equipment and the earliest experimental mobile phones . Modern EEPROM based on Fowler-Nordheim tunnelling to erase data was invented by Bernward and patented by Siemens in 1974. And further developed between 1976 and 1978 by Eliyahou Harari at Hughes Aircraft Company and George Perlegos and others at Intel. This led to Masuoka's invention of flash memory at Toshiba in 1980. The improvement between EEPROM and flash being that flash
6328-430: 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
6441-424: 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
6554-601: 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
6667-408: 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
6780-630: 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
6893-438: The FG is charged. The binary value of the cell is sensed by determining whether there is current flowing through the transistor when V I is asserted on the CG. In a multi-level cell device, which stores more than one bit per cell, the amount of current flow is sensed (rather than simply its presence or absence), in order to determine more precisely the level of charge on the FG. Floating gate MOSFETs are so named because there
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#17328523696617006-537: The I/O interface of NAND flash does not provide a random-access external address bus. Rather, data must be read on a block-wise basis, with typical block sizes of hundreds to thousands of bits. This makes NAND flash unsuitable as a drop-in replacement for program ROM, since most microprocessors and microcontrollers require byte-level random access. In this regard, NAND flash is similar to other secondary data storage devices , such as hard disks and optical media , and
7119-696: 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
7232-494: 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
7345-500: 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
7458-454: 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
7571-466: The cell block. Older memories used source erase, in which a high voltage was applied to the source and then electrons from the FG were moved to the source. Modern NOR flash memory chips are divided into erase segments (often called blocks or sectors). The erase operation can be performed only on a block-wise basis; all the cells in an erase segment must be erased together. Programming of NOR cells, however, generally can be performed one byte or word at
7684-502: The cell by increasing the MOSFET's threshold voltage. This, in turn, changes the drain-source current that flows through the transistor for a given gate voltage, which is ultimately used to encode a binary value. The Fowler-Nordheim tunneling effect is reversible, so electrons can be added to or removed from the floating gate, processes traditionally known as writing and erasing. Despite the need for relatively high programming and erasing voltages, virtually all flash chips today require only
7797-402: The cells are logically set to 1. Data can only be programmed in one pass to a page in a block that was erased. The programming process is set one or more cells from 1 to 0. Any cells that have been set to 0 by programming can only be reset to 1 by erasing the entire block. This means that before new data can be programmed into a page that already contains data, the current contents of the page plus
7910-776: 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, 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
8023-484: 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
8136-584: The control or periphery circuitry. This increases the number of IO operations per flash chip or die, but it also introduces challenges when building capacitors for charge pumps used to write to the flash memory. Some flash dies have as many as 6 planes. As of August 2017, microSD cards with a capacity up to 400 GB (400 billion bytes) are available. The same year, Samsung combined 3D IC chip stacking with its 3D V-NAND and TLC technologies to manufacture its 512 GB KLUFG8R1EM flash memory chip with eight stacked 64-layer V-NAND chips. In 2019, Samsung produced
8249-404: The core of the removable USB storage devices known as USB flash drives , as well as most memory card formats and solid-state drives available today. The hierarchical structure of NAND flash starts at a cell level which establishes strings, then pages, blocks, planes and ultimately a die. A string is a series of connected NAND cells in which the source of one cell is connected to the drain of
8362-440: 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
8475-480: 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
8588-416: 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
8701-497: The first commercial NOR type flash chip in 1988. NOR-based flash has long erase and write times, but provides full address and data buses , allowing random access to any memory location . This makes it a suitable replacement for older read-only memory (ROM) chips, which are used to store program code that rarely needs to be updated, such as a computer's BIOS or the firmware of set-top boxes . Its endurance may be from as little as 100 erase cycles for an on-chip flash memory, to
8814-465: 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
8927-462: The flash storage device (such as SSD ), the data actually written to the flash memory may be 0011 1100. Vertical NAND (V-NAND) or 3D NAND memory stacks memory cells vertically and uses a charge trap flash architecture. The vertical layers allow larger areal bit densities without requiring smaller individual cells. It is also sold under the trademark BiCS Flash , which is a trademark of Kioxia Corporation (formerly Toshiba Memory Corporation). 3D NAND
9040-418: The floating gate. This is why data retention goes down and the risk of data loss increases with increasing degradation. The silicon oxide in a cell degrades with every erase operation. The degradation increases the amount of negative charge in the cell over time due to trapped electrons in the oxide and negates some of the control gate voltage, this over time also makes erasing the cell slower, so to maintain
9153-435: The high Vpp voltage for all flash chips in an SSD with a single shared external boost converter. In spacecraft and other high-radiation environments, the on-chip charge pump is the first part of the flash chip to fail, although flash memories will continue to work – in read-only mode – at much higher radiation levels. In NOR flash, each cell has one end connected directly to ground, and
9266-415: The higher charged FG threshold voltage (V T2 ) by changing the FG charge. In order to read a value from the cell, an intermediate voltage (V I ) between V T1 and V T2 is applied to the CG. If the channel conducts at V I , the FG must be uncharged (if it were charged, there would not be conduction because V I is less than V T2 ). If the channel does not conduct at the V I , it indicates that
9379-403: 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
9492-654: 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
9605-810: The large block sizes used in flash memory erasing give it a significant speed advantage over non-flash EEPROM when writing large amounts of data. As of 2019, flash memory costs greatly less than byte-programmable EEPROM and had become the dominant memory type wherever a system required a significant amount of non-volatile solid-state storage . EEPROMs, however, are still used in applications that require only small amounts of storage, e.g. in SPD implementations on computer memory modules. Flash memory packages can use die stacking with through-silicon vias and several dozen layers of 3D TLC NAND cells (per die) simultaneously to achieve capacities of up to 1 tebibyte per package using 16 stacked dies and an integrated flash controller as
9718-659: The microSD card has an area of just over 1.5 cm , with a thickness of less than 1 mm. NAND flash has achieved significant levels of memory density as a result of several major technologies that were commercialized during the late 2000s to early 2010s. NOR flash was the most common type of Flash memory sold until 2005, when NAND flash overtook NOR flash in sales. Multi-level cell (MLC) technology stores more than one bit in each memory cell . NEC demonstrated multi-level cell (MLC) technology in 1998, with an 80 Mb flash memory chip storing 2 bits per cell. STMicroelectronics also demonstrated MLC in 2000, with
9831-422: The new data must be copied to a new, erased page. If a suitable erased page is available, the data can be written to it immediately. If no erased page is available, a block must be erased before copying the data to a page in that block. The old page is then marked as invalid and is available for erasing and reuse. This is different from operating system LBA view, for example, if operating system writes 1100 0011 to
9944-414: The next one. Depending on the NAND technology, a string typically consists of 32 to 128 NAND cells. Strings are organised into pages which are then organised into blocks in which each string is connected to a separate line called a bitline. All cells with the same position in the string are connected through the control gates by a wordline. A plane contains a certain number of blocks that are connected through
10057-474: The nitride, leading to degradation. Leakage is exacerbated at high temperatures since electrons become more excited with increasing temperatures. CTF technology however still uses a tunneling oxide and blocking layer which are the weak points of the technology, since they can still be damaged in the usual ways (the tunnel oxide can be degraded due to extremely high electric fields and the blocking layer due to Anode Hot Hole Injection (AHHI). Degradation or wear of
10170-413: The number of bits increases, the number of possible states also increases and thus the cell is less tolerant of adjustments to programming voltages, because there is less space between the voltage levels that define each state in a cell. The process of moving electrons from the control gate and into the floating gate is called Fowler–Nordheim tunneling , and it fundamentally changes the characteristics of
10283-527: 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
10396-471: 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 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
10509-425: 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
10622-516: The other end connected directly to a bit line. This arrangement is called "NOR flash" because it acts like a NOR gate: when one of the word lines (connected to the cell's CG) is brought high, the corresponding storage transistor acts to pull the output bit line low. NOR flash continues to be the technology of choice for embedded applications requiring a discrete non-volatile memory device. The low read latencies characteristic of NOR devices allow for both direct code execution and data storage in
10735-435: The oxides is the reason why flash memory has limited endurance, and data retention goes down (the potential for data loss increases) with increasing degradation, since the oxides lose their electrically insulating characteristics as they degrade. The oxides must insulate against electrons to prevent them from leaking which would cause data loss. In 1991, NEC researchers including N. Kodama, K. Oyama and Hiroki Shirai described
10848-413: The performance and reliability of the NAND chip, the cell must be retired from use. Endurance also decreases with the number of bits in a cell. With more bits in a cell, the number of possible states (each represented by a different voltage level) in a cell increases and is more sensitive to the voltages used for programming. Voltages may be adjusted to compensate for degradation of the silicon oxide, and as
10961-539: 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
11074-454: The relatively thin oxide, gradually degrading its electrically insulating properties and allowing electrons to be trapped in and pass through freely (leak) from the floating gate into the oxide, increasing the likelihood of data loss since the electrons (the quantity of which is used to represent different charge levels, each assigned to a different combination of bits in MLC Flash) are normally in
11187-610: 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
11300-410: The same bitline. A flash die consists of one or more planes, and the peripheral circuitry that is needed to perform all the read, write, and erase operations. The architecture of NAND flash means that data can be read and programmed (written) in pages, typically between 4 KiB and 16 KiB in size, but can only be erased at the level of entire blocks consisting of multiple pages. When a block is erased, all
11413-407: The same silicon nitride material. An individual memory cell is made up of one planar polysilicon layer containing a hole filled by multiple concentric vertical cylinders. The hole's polysilicon surface acts as the gate electrode. The outermost silicon dioxide cylinder acts as the gate dielectric, enclosing a silicon nitride cylinder that stores charge, in turn enclosing a silicon dioxide cylinder as
11526-405: The same term [REDACTED] This disambiguation page lists articles associated with the title SLIC . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=SLIC&oldid=1066062013 " Category : Disambiguation pages Hidden categories: Short description
11639-672: 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
11752-531: 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
11865-479: 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
11978-405: 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
12091-418: The tunnel dielectric that surrounds a central rod of conducting polysilicon which acts as the conducting channel. Memory cells in different vertical layers do not interfere with each other, as the charges cannot move vertically through the silicon nitride storage medium, and the electric fields associated with the gates are closely confined within each layer. The vertical collection is electrically identical to
12204-457: 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
12317-777: 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
12430-633: The year 2000, most BIOSes provide ACPI , SMBIOS , VBE and e820 interfaces for modern operating systems. 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 . Flash memory Flash memory is an electronic non-volatile computer memory storage medium that can be electrically erased and reprogrammed. The two main types of flash memory, NOR flash and NAND flash , are named for
12543-417: Was first announced by Toshiba in 2007. V-NAND was first commercially manufactured by Samsung Electronics in 2013. V-NAND uses a charge trap flash geometry (which was commercially introduced in 2002 by AMD and Fujitsu ) that stores charge on an embedded silicon nitride film. Such a film is more robust against point defects and can be made thicker to hold larger numbers of electrons. V-NAND wraps
12656-616: Was invented by Fujio Masuoka at Toshiba in 1980 and is based on EEPROM technology. Toshiba began marketing flash memory in 1987. EPROMs had to be erased completely before they could be rewritten. NAND flash memory, however, may be erased, written, and read in blocks (or pages), which generally are much smaller than the entire device. NOR flash memory allows a single machine word to be written – to an erased location – or read independently. A flash memory device typically consists of one or more flash memory chips (each holding many flash memory cells), along with
12769-433: 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
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