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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.
This allowed the 360's ISA to be expansive, and this became the paragon of computer design in the 1960s and 70s, the so-called orthogonal design. This style of memory access with wide variety of modes led to instruction sets with hundreds of different instructions, a style known today as CISC (Complex Instruction Set Computing).
The VAX ISA is considered a complex instruction set computer (CISC) design. DEC quickly dropped the −11 branding as PDP-11 compatibility was no longer a major concern. The line expanded to both high-end mainframes like the VAX 9000 as well as to the workstation -scale systems like the VAXstation series.
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 ...
Classic Complex Instruction Set Computer (CISC) ISAs optimized by providing a larger set of more complex CPU instructions. Generally speaking, however, complex instructions inflate the number of clock cycles per instruction C l o c k C y c l e s I n s t r u c t i o n {\displaystyle \mathrm {\tfrac {ClockCycles}{Instruction}} } because they must ...
z/Architecture, initially and briefly called ESA Modal Extensions (ESAME), is IBM's 64-bit complex instruction set computer (CISC) instruction set architecture, implemented by its mainframe computers. IBM introduced its first z/Architecture-based system, the z900, in late 2000. [1]
The x86 instruction set refers to the set of instructions that x86-compatible microprocessors support. 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 ...