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The instruction cycle (also known as the fetch–decode–execute cycle, or simply the fetch–execute cycle) is the cycle that the central processing unit (CPU) follows from boot-up until the computer has shut down in order to process instructions. It is composed of three main stages: the fetch stage, the decode stage, and the execute stage.
In computer science, instruction scheduling is a compiler optimization used to improve instruction-level parallelism, which improves performance on machines with instruction pipelines. Put more simply, it tries to do the following without changing the meaning of the code:
In computer engineering, instruction pipelining is a technique for implementing instruction-level parallelism within a single processor. Pipelining attempts to keep every part of the processor busy with some instruction by dividing incoming instructions into a series of sequential steps (the eponymous "pipeline") performed by different processor units with different parts of instructions ...
Load IDTR (Interrupt Descriptor Table Register) from memory. [b] The IDTR controls not just the address/size of the IDT (interrupt Descriptor Table) in protected mode, but the IVT (Interrupt Vector Table) in real mode as well. LMSW r/m16: 0F 01 /6: Load MSW (Machine Status Word) from 16-bit register or memory. [c] [d] CLTS: 0F 06
For example, hardware timers send interrupts to the CPU at regular intervals. Most operating systems execute a HLT instruction when there is no immediate work to be done, putting the processor into an idle state. In Windows NT, for example, this instruction is run in the "System Idle Process". On x86 processors, the opcode of HLT is 0xF4.
The first machine to use out-of-order execution was the CDC 6600 (1964), designed by James E. Thornton, which uses a scoreboard to avoid conflicts. It permits an instruction to execute if its source operand (read) registers aren't to be written to by any unexecuted earlier instruction (true dependency) and the destination (write) register not be a register used by any unexecuted earlier ...
An interrupt vector table (IVT) is a data structure that associates a list of interrupt handlers with a list of interrupt requests in a table of interrupt vectors. Each entry of the interrupt vector table, called an interrupt vector, is the address of an interrupt handler (also known as ISR). While the concept is common across processor ...
IRQ 9 – Advanced Configuration and Power Interface (ACPI) system control interrupt on Intel chipsets. [6] And/or left for the use of peripherals (use depends on OS) IRQ 10 – The interrupt is left for the use of peripherals (for example, SCSI or NIC) IRQ 11 – The interrupt is left for the use of peripherals (for example, SCSI or NIC)