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The instructions are usually part of an executable program, often stored as a computer file and executed on the processor. The x86 instruction set has been extended several times, introducing wider registers and datatypes as well as new functionality.
An instruction set architecture is distinguished from a microarchitecture, which is the set of processor design techniques used, in a particular processor, to implement the instruction set. Processors with different microarchitectures can share a common instruction set.
Because a program normally relies on such factors, different systems will typically not run the same machine code, even when the same type of processor is used. A processor's instruction set may have fixed-length or variable-length instructions. How the patterns are organized varies with the particular architecture and type of instruction.
Complex instructions are implemented by microcode that consists of predefined sequences of micro-operations. [22] Some processor designs use machine code that runs in a special mode, with special instructions, available only in that mode, that have access to processor-dependent hardware, to implement some low-level features of the instruction set.
Starting with the Pentium Pro, in most Intel x86 processors, instructions are converted by the instruction fetch and decode unit to sequences of processor-specific micro-operations that are directly executed by the processor. For the instructions that are implemented in microcode, the microcode consists of micro-operations fetched from on-chip ...
In computing, an opcode (abbreviated from operation code) [1] [2] is an enumerated value that specifies the operation to be performed. Opcodes are employed in hardware devices such as arithmetic logic units (ALUs) and central processing units (CPUs) as well as in some software instruction sets.
x86 assembly language is a family of low-level programming languages that are used to produce object code for the x86 class of processors. These languages provide backward compatibility with CPUs dating back to the Intel 8008 microprocessor, introduced in April 1972.
Minimal instruction set computer (MISC) is a central processing unit (CPU) architecture, usually in the form of a microprocessor, with a very small number of basic operations and corresponding opcodes, together forming an instruction set.