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In computer science
Computer science

Computer science is the study of the theoretical foundations of information and computation, and of practical techniques for their implementation and application in computer systems....
 and more specifically the x86 architecture, HLT is an assembly language
Assembly language

An assembly language is a low-level language for programming computers. It implements a symbolic representation of the numeric machine codes and other constants needed to program a particular CPU architecture....
 instruction which halts the CPU until the next external interrupt
Interrupt

In computing, an interrupt is an asynchronous communication signal from hardware indicating the need for attention or a synchronous event in software indicating the need for a change in execution....
 is fired. Most of the commonly used devices use interrupts for their interaction with drivers. The HLT instruction is run when an operating system
Operating system

An operating system is an interface between hardware and applications; it is responsible for the management and coordination of activities and the sharing of the limited resources of the computer....
 enters its idle loop and there is no immediate work to be done. In Windows NT
Windows NT

Windows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It was originally designed to be a powerful high-level-language-based, processor-independent, multiprocessing, multiuser operating system with features comparable to Unix....
 for example, this instruction is run in the 'System Idle Process
System idle process

In Windows NT operating systems, the System Idle Process contains one or more Kernel thread which run when no other runnable thread can be scheduled on a CPU....
'.

Process
Almost every reasonably modern processor instruction set
Instruction set

An instruction set is a list of all the instruction , and all their variations, that a processor can execute.Instructions include:* Arithmetic such as add and subtract...
 includes an instruction which halts the processor until more work needs to be done.






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Encyclopedia


In computer science
Computer science

Computer science is the study of the theoretical foundations of information and computation, and of practical techniques for their implementation and application in computer systems....
 and more specifically the x86 architecture, HLT is an assembly language
Assembly language

An assembly language is a low-level language for programming computers. It implements a symbolic representation of the numeric machine codes and other constants needed to program a particular CPU architecture....
 instruction which halts the CPU until the next external interrupt
Interrupt

In computing, an interrupt is an asynchronous communication signal from hardware indicating the need for attention or a synchronous event in software indicating the need for a change in execution....
 is fired. Most of the commonly used devices use interrupts for their interaction with drivers. The HLT instruction is run when an operating system
Operating system

An operating system is an interface between hardware and applications; it is responsible for the management and coordination of activities and the sharing of the limited resources of the computer....
 enters its idle loop and there is no immediate work to be done. In Windows NT
Windows NT

Windows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It was originally designed to be a powerful high-level-language-based, processor-independent, multiprocessing, multiuser operating system with features comparable to Unix....
 for example, this instruction is run in the 'System Idle Process
System idle process

In Windows NT operating systems, the System Idle Process contains one or more Kernel thread which run when no other runnable thread can be scheduled on a CPU....
'.

Process


Almost every reasonably modern processor instruction set
Instruction set

An instruction set is a list of all the instruction , and all their variations, that a processor can execute.Instructions include:* Arithmetic such as add and subtract...
 includes an instruction which halts the processor until more work needs to be done. In interrupt driven processors this instruction halts the CPU until an external interrupt is received. On most architectures, executing such an instruction allows the processor to significantly reduce its power usage and heat output, which is why it is commonly used instead of busy waiting
Busy waiting

In software engineering, busy waiting or spinning is a technique in which a process repeatedly checks to see if a condition is true, such as waiting for Computer keyboard input or waiting for a lock to become available....
.

Everyday usage

Since issuing the HLT instruction requires ring 0 access, it can only be run by privileged system software, such as the kernel. Because of this, it is often best practice in application programming to use the API provided for that purpose by the operating system when no more work can be done. This allows the kernel to decide if other processes are runnable; if not, it will normally issue the HLT instruction to cut power usage

See also

  • Halt and Catch Fire
    Halt and Catch Fire

    Halt and Catch Fire, known by the mnemonic HCF, was originally a fictitious computer machine code instruction claimed to be under development at IBM for use in their IBM System/360 computers, along with many other amusing instructions such as "Execute Operator"....
  • Idle task
  • X86
  • Computer architecture
    Computer architecture

    Computer architecture in computer engineering is the conceptual design and fundamental operational structure of a computer system. It is a blueprint and functional description of requirements and design implementations for the various parts of a computer, focusing largely on the way by which the central processing unit performs internally an...
  • Instruction set
    Instruction set

    An instruction set is a list of all the instruction , and all their variations, that a processor can execute.Instructions include:* Arithmetic such as add and subtract...