In computer systems programming, an interrupt handler, also known as an interrupt service routine or ISR, is a special block of code associated with a specific interrupt condition. Interrupt handlers are initiated by hardware interrupts, software interrupt instructions, or software exceptions, and are used for implementing device drivers or transitions between protected modes of operation, such as system calls.

<software> A routine which is executed when an interrupt occurs. Interrupt handlers typically deal with low-level events in the hardware of a computer system such as a character arriving at a serial port or a tick of a real-time clock. Special care is required when writing an interrupt handler to ensure that either the interrupt which triggered the handler's execution is masked out (inhibitted) until the handler exits, or the handler is re-entrant so that multiple concurrent invocations will not interfere with each other. If interrupts are masked then the handler must execute as quickly as possible so that important events are not missed. This is often arranged by splitting the processing associated with the event into "upper" and "lower" halves. The lower part is the interrupt handler which masks out further interrupts as required, checks that the appropriate event has occurred (this may be necessary if several events share the same interrupt), services the interrupt, e.g. by reading a character from a UART and writing it to a queue, and re-enabling interrupts. The upper half executes as part of a user process. It waits until the interrupt handler has run. Normally the {operating system} is responsible for reactivating a process which is waiting for some low-level event. It detects this by a shared flag or by inspecting a shared queue or by some other synchronisation mechanism. It is important that the upper and lower halves do not interfere if an interrupt occurs during the execution of upper half code. This is usually ensured by disabling interrupts during critical sections of code such as removing a character from a queue. (2002-07-24)

A raster interrupt (also called a horizontal blank interrupt) is an interrupt signal in a legacy computer system which is used for display timing. It is usually, though not always, generated by a system's graphics chip as the scan lines of a frame are being readied to send to the monitor for display.

The Interrupt Descriptor Table (IDT) is a data structure used by the x86 architecture to implement an interrupt vector table. The IDT is used by the processor to determine the correct response to interrupts and exceptions.

(interrupts, interrupting, interrupted)

An interrupt caused by a specific machine language operation code (e.g. the Motorola 68000's TRAP, the {IBM System/390}'s SVC or the ARM's SWI) rather than by a hardware event. As with a hardware interrupt, this causes the processor to store the current state, store identifying information about the particular interrupt, and pass control to a first level interrupt handler. A trap is similar except that it is caused by an unexpected software condition or error (e.g. divide by zero, undefined instruction) rather than a deliberate instruction. (1995-02-14)

v. a.

interrupt

External sorting is a class of sorting algorithms that can handle massive amounts of data. External sorting is required when the data being sorted do not fit into the main memory of a computing device (usually RAM) and instead they must reside in the slower external memory, usually a disk drive.