The 8259A is an improved version of the 8259 Programmable Interrupt Controller. Both provide eight IRQ (interrupt request) lines, numbered 0–7. The device was originally designed by Intel and meant to work with the 8-bit Intel 8085 and 16-bit Intel 8086 microprocessors. NEC apparently created the 8259A, although the design has been widely duplicated. The 8259(A) was used in the original IBM PC, and provided the standard used for the next 20 years (and beyond). In 1984, a second controller, commonly called the 8259B to differentiate it, was added in the IBM AT, extending the ISA bus architecture. The IRQ2 pins on each chip were connected together, so a device on that bus wire could be configured as either operating on IRQ2 or IRQ9 (the second set of IRQ lines were numbered 8–15). A Programmable Interrupt Controller (PIC) is a device which allows priority levels to be assigned to its interrupt outputs. ... An IRQ or interrupt request is the means by which hardware components request computing time from the CPU. IRQs for IBM PC compatible computers The modern IBM PC compatible computer has 16 IRQ assignments (0-15), each one representing a different physical (or virtual) piece of hardware. ... In computer science, an interrupt is a signal from a device which typically results in a context switch: that is, the processor sets aside what its doing and does something else. ... Intel Corporation (NASDAQ: INTC) (HKSE: 4335) (founded 1968) is a U.S.-based multinational corporation that is best known for designing and manufacturing microprocessors and specialized integrated circuits. ... The Intel 8085 was an 8-bit microprocessor made by Intel in the mid-1970s. ... An Intel 8086 Microprocessor The 8086 is a 16-bit microprocessor chip designed by Intel in 1978, which gave rise to the x86 architecture. ... Microprocessors, including an Intel 80486DX2 and an Intel 80386 A microprocessor (abbreviated as µP or uP) is a computer electronic component made from miniaturized transistors on a single semiconductor integrated circuit (IC) (aka microchip or just chip). ... IBM PC (IBM 5150) with keyboard and green screen monochrome monitor (IBM 5151), running MS-DOS 5. ... This page is about the year 1984. ... The IBM AT, more formally known as the PC AT or PC/AT, was IBMs third-generation PC, designed around the Intel 80286 microprocessor and released in 1984. ... Industry Standard Architecture (in practice almost always shortened to ISA) is a bus standard for IBM compatibles introduced in 1984 that extends the XT bus architecture to 16 bits. ... In computer architecture, a bus is a subsystem that transfers data or power between computer components inside a computer or between computers. ...

This convoluted arrangement finally began to disappear in the late 1990s and early 2000s, initially on multiprocessor systems. It has been succeeded by Advanced Programmable Interrupt Controllers, specifically Intel's IO-APIC. IO-APIC systems still emulate an 8259 environment by default and retain a certain level of compatibility while in advanced mode. Non-PC compatible systems never had this arrangement. // Events and trends The 1990s in its most obvious sense refers to the years 1990 to 1999, but has held a strong influence into the 2000s. ... Saddam Hussein shortly after his capture Major controversy over U. S. presidential election (November 7-December 13, 2000) September 11, 2001 terrorist attack on New Yorks World Trade Center and Virginias Pentagon killing almost 3000 people. ... Multiprocessing is traditionally known as the use of multiple concurrent processes in a system as opposed to a single process at any one instant. ... An Advanced Programmable Interrupt Controller (APIC) is a more intricate Programmmable Interrupt Controller (PIC). ... Intel Corporation (NASDAQ: INTC) (HKSE: 4335) (founded 1968) is a U.S.-based multinational corporation that is best known for designing and manufacturing microprocessors and specialized integrated circuits. ... IO-APIC (I/O Advanced Programmable Interrupt Controller) is an Intel architecture for dealing with interrupts in multi-processor computer systems. ...

IRQs in the PC AT environment

• IRQ0 – 8253/8254 interval timer (System Timer)
• IRQ1 – keyboard
• IRQ2 – reserved for the 8259B (Tied to IRQ 9)
• IRQ3 – COM2 and COM4
• IRQ4 – COM1 and COM3
• IRQ5 – LPT2
• IRQ6 – Floppy controller
• IRQ7 – LPT1
• IRQ8 – Real-time clock (RTC)
• IRQ9 – Bridged to IRQ2
• IRQ10 – Not Assigned
• IRQ11 – Not Assigned
• IRQ12 – PS/2 mouse
• IRQ13 – Math coprocessor
• IRQ14 – Primary IDE controller
• IRQ15 – Secondary IDE controller

IRQ7 was initially a common choice for use of a sound card, but it was found that this would interfere with the printer port (LPT1), so IRQ5 later became the most prevalent choice. Serial ports (COMx) could frequently be disabled in order to make another port available. However, the common literature which says "COM1 and COM3" (for instance) turned out to be rather misleading, as it was nearly impossible to operate two serial ports on a single IRQ. The Intel 8253/8254 is a programmable interval timer chip used to perform timing and counting functions, found on all x86 PCs. ... The Intel 8253/8254 is a programmable interval timer chip (PIT) used to perform timing and counting functions, found on all x86 PCs. ... A computer keyboard is a peripheral modelled after the typewriter keyboard. ... RS-232 (also referred to as EIA RS-232C or V.24) is a standard for serial binary data interchange between a DTE (Data terminal equipment) and a DCE (Data communication equipment). ... LPT is the original, yet still common, name of the parallel port interface on IBM PC-compatible computers. ... 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 real-time clock (RTC) is a computer clock (most often in the form of an integrated circuit chip) that keeps track of the current time even when the computer is turned off. ... PS/2 can refer to: IBM Personal System/2, a series of post-PC computers sold by IBM starting in 1987. ... Operating a mechanical 1: Pulling the mouse turns the ball. ... A coprocessor is a computer processor used to supplement the functions of the primary processor (the CPU). ... ATA cables: 40 wire ribbon cable top, 80 wire ribbon cable bottom Advanced Technology Attachment (ATA) is a standard interface for connecting storage devices such as hard disks and CD-ROM drives inside personal computers. ... ATA cables: 40 wire ribbon cable top, 80 wire ribbon cable bottom Advanced Technology Attachment (ATA) is a standard interface for connecting storage devices such as hard disks and CD-ROM drives inside personal computers. ... A sound card based on VIA Envy chip A sound card is a computer expansion card that can input and output sound under program control. ... A male DE-9 serial port on the rear panel of a PC. In computing, a serial port is an interface on a computer system with which information is transferred in or out one bit at a time (contrast parallel port). ...

IRQ sharing became more practical on PCI-based systems, but it could still be problematic in some cases. This resulted in a few interrupts being very heavily used, while others would see very little use. In modern systems, IRQ selection is completely automatic, and users can only make manual alterations on some systems (many manufacturers hide such configuration options). 32-bit PCI expansion slots on a motherboard 64-bit PCI expansion slots inside a Power Macintosh G4 The Peripheral Component Interconnect standard (in practice almost always shortened to PCI) specifies a computer bus for attaching peripheral devices to a computer motherboard. ...

See Also

• Programmable Interrupt Controller
• Advanced Programmable Interrupt Controller
• IO-APIC
• IRQ

A Programmable Interrupt Controller (PIC) is a device which allows priority levels to be assigned to its interrupt outputs. ... An Advanced Programmable Interrupt Controller (APIC) is a more intricate Programmmable Interrupt Controller (PIC). ... IO-APIC (I/O Advanced Programmable Interrupt Controller) is an Intel architecture for dealing with interrupts in multi-processor computer systems. ... An IRQ or interrupt request is the means by which hardware components request computing time from the CPU. IRQs for IBM PC compatible computers The modern IBM PC compatible computer has 16 IRQ assignments (0-15), each one representing a different physical (or virtual) piece of hardware. ...

External links

• 8259(A) Programmable Interrupt Controller (PIC)
• 8259 Programmable Interrupt Controller