- HLT
In
computer science and more specifically thex86 architecture, HLT is anassembly language instruction which halts the CPU until the next externalinterrupt is fired. [cite web |url=http://developer.intel.com/design/pentiumii/manuals/243191.htm|title=Intel Architecture Software Developer's Manual, Volume 2: Instruction Set Reference Manual|accessdate=2007-07-13] This interrupt usually comes from the clock. The HLT instruction is run when anoperating system enters its idle loop and there is no immediate work to be done. InWindows NT for example, this instruction is run in the 'System Idle Process '.HLT machine instruction
Almost every reasonably modern processor
instruction set 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 fired. 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 ofbusy waiting .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 usageee also
*
Halt and Catch Fire
*Idle task
*X86
*Computer architecture
*Instruction set References
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