ISA: A Contract Model Of A Computer

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abstract model of a computer. It is the part of a computer that relates to programming (basically machine language). The instruction set supply’s commands to the processor, to tell it what it needs to do. An understanding of an ISA is called an implementation. An instruction set permits multiple implementations that may differ in performance, physical size, and expense etc. because the ISA serves as the interface between software and hardware. An ISA defines everything a machine language programmer needs to know in order to program a computer. What an ISA defines differs between ISAs; in general, ISAs define the supported data types, interrupt, memory architecture, registers, addressing modes, instructions, exception handling, and external input/output model. A very good example of an instruction set is the x86 instruction set, which is often found on computers today. …show more content…

A single "complex" instruction performs a task that may take many instructions on other computers. Such instructions are represented by instructions that take multiple steps, control multiple functional units, or otherwise appear on a larger scale than the bulk of simple instructions implemented by the given processor. Examples of "complex" instructions include: • Transferring multiple registers to or from memory (especially the stack) at once • Moving large blocks of memory (e.g. string copy or DMA transfer) • Complicated integer and floating-point arithmetic (e.g. square root, or transcendental functions such as logarithm, sine, cosine, etc.) • SIMD (single instruction, multiple data) instructions, a single instruction performing an operation on many homogeneous values in parallel, possibly in dedicated SIMD registers • Performing an atomic test-and-set instruction or other read-modify-write atomic instruction • Instructions that perform ALU operations with an operand from memory rather than a

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