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A complex instruction set computer (CISC / ˈ s ɪ s k /) is a computer architecture in which single instructions can execute several low-level operations (such as a load from memory, an arithmetic operation, and a memory store) or are capable of multi-step operations or addressing modes within single instructions.
The first was the CISC (Complex Instruction Set Computer), which had many different instructions. In the 1970s, however, places like IBM did research and found that many instructions in the set could be eliminated. The result was the RISC (Reduced Instruction Set Computer), an architecture that uses a smaller set of instructions.
The approach of increasingly complex microcode-implemented instruction sets was later called complex instruction set computer (CISC). An alternate approach, used in many microprocessors , is to use one or more programmable logic array (PLA) or read-only memory (ROM) (instead of combinational logic) mainly for instruction decoding, and let a ...
A common misunderstanding of the phrase "reduced instruction set computer" is that instructions are simply eliminated, resulting in a smaller set of instructions. [35] In fact, over the years, RISC instruction sets have grown in size, and today many of them have a larger set of instructions than many CISC CPUs.
Comparison of instruction set architectures; Complex instruction set computer; Instruction set architecture; Millicode; Orthogonal instruction set; Reduced instruction set computer; Very long instruction word
An instruction set architecture (ISA) is an abstract model of a computer, also referred to as computer architecture.A realization of an ISA is called an implementation.An ISA permits multiple implementations that may vary in performance, physical size, and monetary cost (among other things); because the ISA serves as the interface between software and hardware.
In computer architecture, millicode is a higher level of microcode used to implement part of the instruction set of a computer. The instruction set for millicode is a subset of the machine's native instruction set, omitting those instructions that are implemented using millicode, plus instructions that provide access to hardware not accessible using the native instruction set.
Explicit data graph execution, or EDGE, is a type of instruction set architecture (ISA) which intends to improve computing performance compared to common processors like the Intel x86 line. EDGE combines many individual instructions into a larger group known as a "hyperblock". Hyperblocks are designed to be able to easily run in parallel.