ISA Industry Standard Architecture
Five 16-bit and one 8-bit ISA slots on a motherboard
Year Created:	1981
Created By:	IBM
Superseded By:	PCI (1993)
Width:	8 or 16 bits
Number of Devices:	1 per slot
Capacity	8 MHz
Style:	Parallel
Hotplugging?	no
External?	no

Industry Standard Architecture (in practice almost always shortened to ISA) was a computer bus standard for IBM compatible computers. Image File history File links Isa1. ... In computer science, 16-bit is an adjective used to describe integers that are at most two bytes wide, or to describe CPU architectures based on registers, address buses, or data buses of that size. ... 8-bit refers to the number of bits used in the data bus of a computer. ... A motherboard is the central or primary circuit board making up a complex electronic system, such as a modern computer. ... IBM redirects here. ... 64-bit PCI expansion slots inside a Power Macintosh G4 The Peripheral Component Interconnect, or PCI Standard (in practice almost always shortened to PCI) specifies a computer bus for attaching peripheral devices to a computer motherboard. ... This article is about the unit of information. ... In computing, a parallel port is an interface from a computer system where data is transferred in or out in parallel, that is, on more than one wire. ... In computer architecture, a bus is a subsystem that transfers data or power between computer components inside a computer or between computers and typically is controlled by device driver software. ... One of the first PCs from IBM - the IBM PC model 5150. ...

History

ISA originated as an 8-bit system in the IBM PC in 1981, and was extended in 1983 as the XT bus architecture. The newer 16-bit standard, the IBM AT bus, was introduced in 1984. In 1988, the Gang of Nine IBM PC compatible manufacturers put forth the 32-bit EISA standard and in the process retroactively renamed the AT bus to be "ISA" to avoid infringing IBM's trademark on its PC/AT computer. IBM PC (IBM 5150) with keyboard and green screen monochrome monitor (IBM 5151), running MS-DOS 5. ... Year 1981 (MCMLXXXI) was a common year starting on Thursday (link displays the 1981 Gregorian calendar). ... Year 1983 (MCMLXXXIII) was a common year starting on Saturday (link displays the 1983 Gregorian calendar). ... IBM PC (IBM 5150) with keyboard and green screen monochrome monitor (IBM 5151), running MS-DOS 5. ... The IBM Personal Computer/AT (IBM 5170), more commonly known as the IBM AT and also sometimes called the PC AT or PC/AT, was IBMs second-generation PC, designed around the Intel 80286 microprocessor running at 6 MHz and released in 1984. ... Year 1984 (MCMLXXXIV) was a leap year starting on Sunday (link displays the 1984 Gregorian calendar). ... Year 1988 (MCMLXXXVIII) was a leap year starting on Friday (link displays 1988 Gregorian calendar). ... The Gang of Nine was a group of IBM competitors who came together in 1988 to build the EISA architecture, to compete with IBMs MCA. These companies were AST Research, Compaq Computer, Epson, Hewlett-Packard, NEC, Olivetti, Tandy, WYSE, and Zenith Data Systems. ... This article or section does not cite its references or sources. ... This article does not cite any references or sources. ... A retronym is a type of neologism coined for an old object or concept whose original name has come to be used for something else, is no longer unique, or is otherwise inappropriate or misleading. ...

Designed to connect peripheral cards to the motherboard, ISA allows for bus mastering although only the first 16 MiB of main memory is available for direct access. The 8-bit bus ran at 4.77 MHz, while the 16-bit bus operated at 6 or 8 MHz. IBM RT/PC also used the 16-bit bus. It was also available on some non-IBM compatible machines such as the short-lived AT&T Hobbit and later PowerPC based BeBox. A motherboard is the central or primary circuit board making up a complex electronic system, such as a modern computer. ... This article does not cite any references or sources. ... The three-letter acronym MIB may refer to any of several concepts: Management information base, a computing information repository used (for example) by SNMP In marbles, any marble, but esp. ... The IBM RT was a computer based around the PC-AT bus and IBMs ROMP processor, a spin-off of the IBM 801. ... AT&T (formerly an abbreviation for American Telephone and Telegraph) Corporation (NYSE: T) is an American telecommunications company. ... The Hobbit was a microprocessor design of the early 1990s from AT&T. It developed from their CRISP (C-language Reduced Instruction Set Processor) design that was in turn developed from the C Machine experimental efforts in the late 1980s at Bell Labs. ... PowerPC is a RISC microprocessor architecture created by the 1991 Apple–IBM–Motorola alliance, known as AIM. Originally intended for personal computers, PowerPC CPUs have since become popular embedded and high-performance processors as well. ... The BeBox The BeBox was a short-lived dual processor PC, offered by Be Incorporated to run their own operating system, BeOS. The BeBox made its debut in October 1995 (BeBox Dual603-66). ...

In 1987, IBM moved to replace the AT bus with their proprietary Micro Channel Architecture (MCA) in an effort to regain control of the PC architecture, and the PC market. The system was far more advanced than the AT bus, and computer manufacturers responded with the Extended Industry Standard Architecture (EISA) and later, the VESA Local Bus (VLB). In fact, VLB used some parts originally intended for MCA due to the fact that component manufacturers already had the ability to manufacture it. Both were compatible expansions of the AT bus. Year 1987 (MCMLXXXVII) was a common year starting on Thursday (link displays 1987 Gregorian calendar). ... This article or section does not adequately cite its references or sources. ... This article does not cite any references or sources. ... This article or section does not cite any references or sources. ...

Users of ISA-based machines had to know special information about the hardware they were adding to the system. While a handful of devices were essentially "plug-n-play," this was rare. Users frequently had to configure several parameters when adding a new device, such as the IRQ line, I/O address, or DMA channel. MCA had done away with this complication, and PCI actually incorporated many of the ideas first explored with MCA (though it was more directly descended from EISA). Plug and Play is a term used in the computer field to describe a computers ability to have new devices, normally peripherals, added to it without having to restart the computer. ... In computer science, an interrupt is a signal from a device which typically results in a (register) context switch: that is, the processor sets aside what its doing and does something else. ... On a computer system, an I/O address is specific portion of address space in the CPU used to read/write to specific devices within the computer. ... Direct memory access (DMA) is a feature of modern computers that allows certain hardware subsystems within the computer to access system memory for reading and/or writing independently of the central processing unit. ... 64-bit PCI expansion slots inside a Power Macintosh G4 The Peripheral Component Interconnect, or PCI Standard (in practice almost always shortened to PCI) specifies a computer bus for attaching peripheral devices to a computer motherboard. ...

This trouble with configuration eventually led to the creation of ISA PnP, a plug-n-play system that used a combination of modifications to hardware, the system BIOS, and operating system software to automatically manage the nitty-gritty details. In reality, ISA PnP turned out to be a major headache much of the time, and didn't become well-supported until the architecture was in its final days. This was a major contributor to the use of the phrase "plug-n-pray". Plug and Play is a term used in the computer field to describe a computers ability to have new devices, normally peripherals, added to it without having to restart the computer. ... This article or section does not adequately cite its references or sources. ... // An operating system (OS) is a set of computer programs that manage the hardware and software resources of a computer. ...

PCI slots were the first physically-incompatible expansion ports to directly squeeze ISA off of the motherboard. At first, motherboards were largely ISA, including a few PCI slots. By the mid-1990s, the two slot types were roughly balanced, and ISA slots soon were in the minority of consumer systems. Microsoft's PC 97 specification recommended that ISA slots be removed entirely, though the system architecture still required ISA to be present in some vestigial way internally to handle the floppy drive, serial ports, etc. ISA slots remained for a few more years, and it was even possible to see systems with an Accelerated Graphics Port (AGP) sitting near the central processing unit, an array of PCI slots, and one or two ISA slots near the end. 64-bit PCI expansion slots inside a Power Macintosh G4 The Peripheral Component Interconnect, or PCI Standard (in practice almost always shortened to PCI) specifies a computer bus for attaching peripheral devices to a computer motherboard. ... A motherboard is the central or primary circuit board making up a complex electronic system, such as a modern computer. ... For the band, see 1990s (band). ... Microsoft Corporation, (NASDAQ: MSFT, HKSE: 4338) is a multinational computer technology corporation with global annual revenue of US$44. ... The PC 97 standard is a set of design requirements developed by Microsoft and aimed at making PCs easier to use by maximizing cooperation between the operating system and hardware. ... A floppy disk is a data storage device that comprises a circular piece of thin, flexible (hence floppy) magnetic storage medium encased in a square or rectangular plastic wallet. ... A male DE-9 connector used for a serial port on a PC style computer. ... This article or section does not adequately cite its references or sources. ... Die of an Intel 80486DX2 microprocessor (actual size: 12×6. ...

It is also notable that PCI slots are "rotated" compared to their ISA counterparts—PCI cards were essentially inserted "upside-down," allowing ISA and PCI connectors to squeeze together on the motherboard. Only one of the two connectors can be used in each slot at a time, but this allowed for greater flexibility.

8-bit ISA (XT bus architecture)

The XT bus architecture is an eight-bit ISA bus used by Intel 8086 and Intel 8088 systems in the IBM PC and IBM PC XT in the 1980s. This article is about the unit of information. ... Intel Corporation (NASDAQ: INTC, SEHK: 4335), founded in 1968 as Integrated Electronics Corporation, is an American multinational corporation that is best known for designing and manufacturing microprocessors and specialized integrated circuits. ... The intels 8086 was the first one launched in 1978. ... An Intel 8088 microprocessor The Intel 8088 is an Intel microprocessor based on the 8086, with 16-bit registers and an 8-bit external data bus. ... IBM PC (IBM 5150) with keyboard and green screen monochrome monitor (IBM 5151), running MS-DOS 5. ... The IBM PC/XT (also written PC-XT or PC XT), commonly referred to as the XT, was IBMs successor to the original IBM PC. It was released on March 8, 1983, and was one of the first computers to come standard with a hard drive. ... This article does not cite any references or sources. ...

An 8-bit ISA (XT-bus) mouse adapter

The XT bus has four DMA channels, of which three are brought out to the expansion slots. Of these three, two are normally allocated to machine functions: Image File history File linksMetadata ISA_mouse_adapter. ... Image File history File linksMetadata ISA_mouse_adapter. ... Direct memory access (DMA) is a feature of modern computers that allows certain hardware subsystems within the computer to access system memory for reading and/or writing independently of the central processing unit. ...

The XT bus architecture has single Intel 8259 PIC and eight interrupt lines. Random access memory (usually known by its acronym, RAM) is a type of data storage used in computers. ... A floppy disk is a data storage device that is composed of a disk of thin, flexible (floppy) magnetic storage medium encased in a square or rectangular plastic shell. ... Typical hard drives of the mid-1990s. ... The Intel 8259 is a family of Programmable Interrupt Controllers (PICs) designed and developed for use with the Intel 8085 and Intel 8086 8-bit and 16-bit microprocessors. ... A Programmable Interrupt Controller (PIC) is a device which allows priority levels to be assigned to its interrupt outputs. ...

16-bit ISA (AT bus architecture)

The AT bus architecture is an 16-bit version of the ISA bus first in the IBM PC/AT. This article is about the unit of information. ... IBM PC (IBM 5150) with keyboard and green screen monochrome monitor (IBM 5151), running MS-DOS 5. ...

Technical data

8 bit ISA or XT bus architecture

16 bit ISA Image File history File links Download high resolution version (757x989, 27 KB) Source / Photographer: Appaloosa 20:59, 15 November 2005 (UTC) File links The following pages link to this file: Industry Standard Architecture ... 8-bit refers to the number of bits used in the data bus of a computer. ... Look up pin in Wiktionary, the free dictionary. ...

Note: The ISA bus speed is actually synchronous with the CPU clock speed, resulting in many differing clock speeds, due to the many different speed machines produced by the many 'IBM clone' manufacturers. This led to problems by the late 1980's, where certain ISA cards would suffer compatibility problems and malfunctions when fitted to machines with bus speeds as high as 16MHz. This problem was solved with later, highly integrated chipsets that (generally) standardized the 16-bit ISA bus to 8MHz; this was achieved by under-clocking the CPU to 8MHz only during ISA bus accesses. Image File history File links Download high resolution version (970x1537, 46 KB) Source / Photographer: Appaloosa 21:00, 15 November 2005 (UTC) File links The following pages link to this file: Industry Standard Architecture ... In computer science, 16-bit is an adjective used to describe integers that are at most two bytes wide, or to describe CPU architectures based on registers, address buses, or data buses of that size. ... Look up pin in Wiktionary, the free dictionary. ... A mebibyte (a contraction of mega binary byte) is a unit of information or computer storage, abbreviated MiB. 1 MiB = 220 bytes = 1,048,576 bytes = 1,024 kibibytes 1 MiB = 1024 (= 210) kibibytes (KiB), and 1024 MiB equal one gibibyte (GiB). ... Look up second in Wiktionary, the free dictionary. ... A mebibyte (a contraction of mega binary byte) is a unit of information or computer storage, abbreviated MiB. 1 MiB = 220 bytes = 1,048,576 bytes = 1,024 kibibytes 1 MiB = 1024 (= 210) kibibytes (KiB), and 1024 MiB equal one gibibyte (GiB). ... Look up second in Wiktionary, the free dictionary. ...

Current use

Apart from specialized industrial use, ISA is all but gone today. Even where present, system manufacturers often shield customers from the term "ISA bus", referring to it instead as the "legacy bus" (see legacy system). The PC/104 bus, used in industrial and embedded applications, is a derivative of the ISA bus, utilizing the same signal lines with different connectors. The LPC bus has replaced the ISA bus as the connection to the legacy I/O devices on recent motherboards; while physically quite different, LPC looks just like ISA to software, so that the peculiarities of ISA such as the 16 MiB DMA limit are likely to stick around for a while. It has been suggested that Legacy code be merged into this article or section. ... // PC/104 PC/104 (or PC104) is an embedded computer standard controlled by the PC/104 Consortium, that defines both a form factor and computer bus. ... Low Pin Count interface IT8705F. Involved in fan speed control, floppy and keyboard management, smart card reader, MIDI interface and many other tasks (described in [1]). The Low Pin Count bus, or LPC bus, is used on PC-style personal computers to connect low-bandwidth devices to the CPU, such...

Starting with Windows Vista, Microsoft is phasing out support for ISA cards in Windows. Vista still supports ISA-PnP for the time being, although it's not enabled by default. Windows Vista is a line of graphical operating systems used on personal computers, including home and business desktops, notebook computers, Tablet PCs, and media centers. ...

Standardization

IEEE started a standardization of the ISA bus in 1985, called the P996 specification. However, despite even books being published on the P996 specification, it has never officially gotten past draft status. Year 1985 (MCMLXXXV) was a common year starting on Tuesday (link displays 1985 Gregorian calendar). ...

References

• Microsoft (1999-06-02). "Removing the ISA Architecture in Windows-Based Platforms" (Microsoft Word). Microsoft.
• Microsoft (2001-12-04). "IDs and Serial Numbers for ISA Plug and Play". Microsoft.
• Microsoft (2007-03-15). "Removing Support for Industry Standard Architecture (ISA) Bus". Microsoft.

Year 1999 (MCMXCIX) was a common year starting on Friday (link will display full 1999 Gregorian calendar). ... is the 153rd day of the year (154th in leap years) in the Gregorian calendar. ... Year 2001 (MMI) was a common year starting on Monday (link displays the 2001 Gregorian calendar). ... December 4th redirects here. ... Year 2007 (MMVII) is now the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 74th day of the year (75th in leap years) in the Gregorian calendar. ...

See also

• Extended Industry Standard Architecture (EISA)
• Micro Channel architecture (MCA)
• NuBus
• VESA Local Bus (VESA)
• Peripheral Component Interconnect (PCI)
• Accelerated Graphics Port (AGP)
• PCI Express (PCIe)
• PC/104
• LPC bus
• Switched fabric
• List of device bandwidths

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL. This article does not cite any references or sources. ... This article or section does not adequately cite its references or sources. ... NuBus is a 32-bit parallel computer bus, originally developed at MIT as a part of the NuMachine workstation project, and eventually used by Apple Computer and NeXT Computer. ... This article or section does not cite any references or sources. ... 64-bit PCI expansion slots inside a Power Macintosh G4 The Peripheral Component Interconnect, or PCI Standard (in practice almost always shortened to PCI) specifies a computer bus for attaching peripheral devices to a computer motherboard. ... This article or section does not adequately cite its references or sources. ... PCI Express (formerly known as 3GIO for 3rd Generation I/O, not to be mistaken with PCI-X) is an implementation of the PCI computer bus that uses existing PCI programming concepts and communications standards, but bases it on a much faster serial communications system. ... // PC/104 PC/104 (or PC104) is an embedded computer standard controlled by the PC/104 Consortium, that defines both a form factor and computer bus. ... Low Pin Count interface IT8705F. Involved in fan speed control, floppy and keyboard management, smart card reader, MIDI interface and many other tasks (described in [1]). The Low Pin Count bus, or LPC bus, is used on PC-style personal computers to connect low-bandwidth devices to the CPU, such... Switched Fabric is a Fibre Channel topology where many devices connect with each other via Fibre Channel switches. ... This is a list of device bandwidths: the channel capacity (or, more informally, bandwidth) of some computer devices employing methods of data transport is listed by bit/s, kilobit/s (kbit/s), megabit/s (Mbit/s), or gigabit/s (Gbit/s) as appropriate and also MB/s or megabytes per... This article does not cite any references or sources. ... This article or section does not cite any references or sources. ... This article or section does not adequately cite its references or sources. ... 64-bit PCI expansion slots inside a Power Macintosh G4 The Peripheral Component Interconnect, or PCI Standard (in practice almost always shortened to PCI) specifies a computer bus for attaching peripheral devices to a computer motherboard. ... For other meanings of PCI, see PCI (disambiguation). ... PCI Express (formerly known as 3GIO for 3rd Generation I/O, not to be mistaken with PCI-X) is an implementation of the PCI computer bus that uses existing PCI programming concepts and communications standards, but bases it on a much faster serial communications system. ... // PC/104 PC/104 (or PC104) is an embedded computer standard controlled by the PC/104 Consortium, that defines both a form factor and computer bus. ... This article or section does not cite its references or sources. ... The PCMCIA is the Personal Computer Memory Card International Association, an industry trade association that creates standards for notebook computer peripheral devices. ... Low Pin Count interface IT8705F. Involved in fan speed control, floppy and keyboard management, smart card reader, MIDI interface and many other tasks (described in [1]). The Low Pin Count bus, or LPC bus, is used on PC-style personal computers to connect low-bandwidth devices to the CPU, such... Universal Serial Bus (USB) is a serial bus standard to interface devices. ... This article does not cite any references or sources. ... Bold text // “GFDL” redirects here. ...