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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.
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.
A high-level illustration showing the decomposition of machine instructions into micro-operations, performed during typical fetch-decode-execute cycles [1]: 11 . In computer central processing units, micro-operations (also known as micro-ops or μops, historically also as micro-actions [2]) are detailed low-level instructions used in some designs to implement complex machine instructions ...
Processor design is a subfield of computer science and computer engineering (fabrication) that deals with creating a processor, a key component of computer hardware.. The design process involves choosing an instruction set and a certain execution paradigm (e.g. VLIW or RISC) and results in a microarchitecture, which might be described in e.g. VHDL or Verilog.
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.
The processor as a whole operates in an assembly line fashion, with instructions coming in one side and results out the other. Due to the reduced complexity of the classic RISC pipeline , the pipelined core and an instruction cache could be placed on the same size die that would otherwise fit the core alone on a CISC design.
The design of the CPU allows RISC computers few simple addressing modes [2] and predictable instruction times that simplify design of the system as a whole. The conceptual developments of the RISC computer architecture began with the IBM 801 project in the late 1970s, but these were not immediately put into use.
A MISC CPU cannot have one instruction as that is a one instruction set computer. [4] The implemented CPU instructions should by default not support a wide set of inputs, so this typically means an 8-bit or 16-bit CPU. If a CPU has an NX bit, it is more likely to be viewed as being a complex instruction set computer (CISC) or reduced ...