Signal (IPC)

Lovelace's description from Note G.

Signals are standardized messages sent to a running program to trigger specific behavior, such as quitting or error handling.

- Signal (IPC)

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Family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems.

Henry Maudslay's famous early screw-cutting lathes of circa 1797 and 1800.


Exception handling

Process of responding to the occurrence of exceptions – anomalous or exceptional conditions requiring special processing – during the execution of a program.

Computer simulation, one of the main cross-computing methodologies.

Exception handling, if provided, is facilitated by specialized programming language constructs, hardware mechanisms like interrupts, or operating system (OS) inter-process communication (IPC) facilities like signals.


Interrupt is a request for the processor to interrupt currently executing code (when permitted), so that the event can be processed in a timely manner.

interrupt sources and processor handling

On Unix-like operating systems this involves sending a signal such as SIGSEGV, SIGBUS, SIGILL or SIGFPE, which may either call a signal handler or execute a default action (terminating the program).

Kill (command)

The taskkill command on Microsoft Windows
The taskkill command on ReactOS

In computing, is a command that is used in several popular operating systems to send signals to running processes.

Computer program

Sequence of instructions in a programming language that a computer can execute or interpret.

Lovelace's description from Note G.
Zuse Z3 replica on display at Deutsches Museum in Munich
Glenn A. Beck is changing a tube in ENIAC.
Switches for manual input on a Data General Nova 3, manufactured in the mid-1970s
A VLSI integrated-circuit die.
IBM's System/360 (1964) CPU wasn't a microprocessor.
Artist's depiction of Sacramento State University's Intel 8008 microcomputer (1972).
The original IBM Personal Computer (1981) used an Intel 8088 microprocessor.
The DEC VT100 (1978) was a widely used computer terminal.
Prior to programming languages, Betty Jennings and Fran Bilas programmed the ENIAC by moving cables and setting switches.
"Hello, World!" computer program by Brian Kernighan (1978)
A computer program written in an imperative language
A diagram showing that the user interacts with the application software. The application software interacts with the operating system, which interacts with the hardware.
A kernel connects the application software to the hardware of a computer.
Physical memory is scattered around RAM and the hard disk. Virtual memory is one continuous block.
NOT gate.
NAND gate.
NOR gate.
AND gate.
OR gate.
A symbolic representation of an ALU.

The kernel program should provide a communication channel between executing processes. For a large software system, it may be desirable to engineer the system into smaller processes. Processes may communicate with one another by sending and receiving signals.

Polling (computer science)

External device by a client program as a synchronous activity.

Charles Babbage, sometimes referred to as the "father of computing".

An alternative to polling is the use of interrupts, which are signals generated by devices or processes to indicate that they need attention, want to communicate, etc. Although polling can be very simple, in many situations (e.g., multitasking operating systems) it is more efficient to use interrupts because it can reduce processor usage and/or bandwidth consumption.

Event loop

Programming construct or design pattern that waits for and dispatches events or messages in a program.

Charles Babbage, sometimes referred to as the "father of computing".

Signals are received in signal handlers, small, limited pieces of code that run while the rest of the task is suspended; if a signal is received and handled while the task is blocking in, select will return early with EINTR; if a signal is received while the task is CPU bound, the task will be suspended between instructions until the signal handler returns.

Job control (Unix)

Shell's representation for a process group.

Unix System III running on a PDP-11 simulator

This sends the "interrupt" signal (SIGINT), which defaults to terminating the process, though it can be overridden.

Child process

Process created by another process .


The SIGCHLD signal is sent to the parent of a child process when it exits, is interrupted, or resumes after being interrupted.


Common computer command.

Computer simulation, one of the main cross-computing methodologies.

In POSIX systems, the sequence causes the active program to receive SIGINT, the interruption signal.