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Encyclopedia > Complex instruction set computer

A complex instruction set computer (CISC) is a microprocessor instruction set architecture (ISA) in which each instruction can execute several low-level operations, such as a load from memory, an arithmetic operation, and a memory store, all in a single instruction. The term was coined in contrast to reduced instruction set computer (RISC). A microprocessor (sometimes abbreviated µP) is a programmable digital electronic component that incorporates the functions of a central processing unit (CPU) on a single semiconducting integrated circuit (IC). ... An instruction set, or instruction set architecture (ISA), describes the aspects of a computer architecture visible to a programmer, including the native datatypes, instructions, registers, addressing modes, memory architecture, interrupt and exception handling, and external I/O (if any). ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Arithmetic or arithmetics (from the Greek word αριθμός = number) is the oldest and most elementary branch of mathematics, used by almost everyone, for tasks ranging from simple daily counting to advanced science and business calculations. ... In mathematics, an operator is a function that performs some sort of operation on a number, variable, or function. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... The reduced instruction set computer, or RISC, is a microprocessor CPU design philosophy that favors a simpler set of instructions that all take about the same amount of time to execute. ... Reduced Instruction Set Computer (RISC), is a microprocessor CPU design philosophy that favors a smaller and simpler set of instructions that all take about the same amount of time to execute. ...


Before the first RISC processors were designed, many computer architects tried to bridge the "semanticutueruyytrhfghshfhfhfhdfhdh gap" - to design instruction sets to support high-level programming languages by providing "high-level" instructions such as procedure call and return, loop instructions such as "decrement and branch if non-zero" and complex addressing modes to allow data structure and array accesses to be combined into single instructions. The compact nature of such a CISC ISA results in smaller program sizes and fewer calls to main memory, which at the time (the 1960s) resulted in a tremendous savings on the cost of a computer. A typical vision of a computer architecture as a series of abstraction layers: hardware, firmware, assembler, kernel, operating system and applications (see also Tanenbaum 79). ... A high-level programming language is a programming language that, in comparison to low-level programming languages, may be more abstract, easier to use, or more portable across platforms. ... Addressing modes, a concept from computer science, are an aspect of the instruction set architecture in most central processing unit (CPU) designs. ... A computer program is a collection of instructions that describe a task, or set of tasks, to be carried out by a computer. ...


While they achieved their aim of allowing high-level language constructs to be expressed in fewer instructions, it was observed that they did not always result in improved performance. For example, on one processor it was discovered that it was possible to improve performance by not using the procedure call instruction but using a sequence of simpler instructions instead. Furthermore, the more complex the instruction set, the greater the overhead of decoding any given instruction, both in execution time and silicon area. This is particularly true for processors which used microcode to decode the (macro)instructions. In other words, adding a large and complex instruction set to the processor even slowed down the execution of simple instructions. Implementing all these complex instructions also required a great deal of work on the part of the chip designer, and many transistors; this left less room on the processor to optimize performance in other ways. A microprogram is a program consisting of microcode that controls the different parts of a computers central processing unit (CPU). ...


Examples of CISC processors are the System/360, VAX, PDP-11, Motorola 68000 family, and AMD and Intel x86 CPUs. System/360 Model 65 operators console, with register value lamps and toggle switches (middle of picture) and emergency pull switch (upper right). ... VAX is a 32-bit computing architecture that supports an orthogonal instruction set (machine language) and virtual addressing (i. ... The PDP-11 was a 16-bit minicomputer sold by Digital Equipment Corp. ... The Motorola 68000 is a 32-bit CISC microprocessor from Motorola. ... Advanced Micro Devices, Inc. ... Intel Corporation (NASDAQ: INTC, SEHK: 4335), founded in 1968 as Integrated Electronics Corporation, is an American multinational corporation that is best known for designing and manufacturing microprocessors and specialized integrated circuits. ... x86 or 80x86 is the generic name of a microprocessor architecture first developed and manufactured by Intel. ...


The term, like RISC, has become less meaningful with the continued evolution of both CISC and RISC designs and implementations. The first pipelined "CISC" CPUs, such as 486s from Intel, AMD, Cyrix, and IBM, certainly supported every instruction that their predecessors did, but achieved high efficiency only on a fairly simple x86 subset (resembling a non load/store "RISC" instruction set). Modern x86 processors also decode more complex instructions into series of smaller internal "micro-operations" which can thereby be executed in a pipelined (parallel) fashion, thus achieving high performance on a much larger subset of instructions. Reduced Instruction Set Computer (RISC), is a microprocessor CPU design philosophy that favors a smaller and simpler set of instructions that all take about the same amount of time to execute. ... Intel Corporation (NASDAQ: INTC, SEHK: 4335), founded in 1968 as Integrated Electronics Corporation, is an American multinational corporation that is best known for designing and manufacturing microprocessors and specialized integrated circuits. ... Advanced Micro Devices, Inc. ... Cyrix corporate logo Cyrix was a CPU manufacturer that began in 1988 as a specialist supplier of high-performance math co-processors for 286 and 386 systems. ... International Business Machines Corporation (known as IBM or Big Blue; NYSE: IBM) is a multinational computer technology corporation headquartered in Armonk, New York, USA. The company is one of the few information technology companies with a continuous history dating back to the 19th century. ... Reduced Instruction Set Computer (RISC), is a microprocessor CPU design philosophy that favors a smaller and simpler set of instructions that all take about the same amount of time to execute. ... Micro-operations, also known as a micro-ops or μops, are simple, RISC-like microprocessor instructions used by some CISC processors to implement more complex instructions. ...


See also

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL. CPU redirects here. ... Reduced Instruction Set Computer (RISC), is a microprocessor CPU design philosophy that favors a smaller and simpler set of instructions that all take about the same amount of time to execute. ... In computer science, ZISC stands for Zero Instruction Set Computer, which refers to a chip technology based on pure pattern matching and absence of (micro-)instructions in the classical sense. ... A very long instruction word or VLIW CPU architectures implement a form of instruction level parallelism. ... A microprocessor (sometimes abbreviated µP) is a programmable digital electronic component that incorporates the functions of a central processing unit (CPU) on a single semiconducting integrated circuit (IC). ... A BlueGene supercomputer cabinet. ... CPU design is the hardware design of a central processing unit. ... A typical vision of a computer architecture as a series of abstraction layers: hardware, firmware, assembler, kernel, operating system and applications (see also Tanenbaum 79). ... The Free On-line Dictionary of Computing (FOLDOC) is an online, searchable encyclopedic dictionary of computing subjects. ... GNU logo (similar in appearance to a gnu) The GNU Free Documentation License (GNU FDL or simply GFDL) is a copyleft license for free content, designed by the Free Software Foundation (FSF) for the GNU project. ...


  Results from FactBites:
 
Complex instruction set computer - Wikipedia, the free encyclopedia (412 words)
A complex instruction set computer (CISC) is a microprocessor instruction set architecture (ISA) in which each instruction can execute several low-level operations, such as a load from memory, an arithmetic operation, and a memory store, all in a single instruction.
The compact nature of such a CISC ISA results in smaller program sizes and fewer calls to main memory, which at the time (the 1960s) resulted in a tremendous savings on the cost of a computer.
Modern x86 processors also decode more complex instructions into series of smaller internal "micro-operations" which can thereby be executed in a pipelined (parallel) fashion, thus achieving high performance on a much larger subset of instructions.
Complex Instruction Set Computer (271 words)
A Complex Instruction Set Computer (CISC) is an instruction set architecture (ISA) in which each instruction can indicate several low-level operations, such as a load from memory, an arithmetic operations, and a memory store, all in a single instruction.
Examples of CISC processors are the VAX, PDP-11, Motorola 68000 family and the Intel x86/Pentium CPUs.
Modern "CISC" CPUs, such as recent x86 designs like the Pentium 4, whilst they usually support every instruction that their predecessors did, are designed to work most efficiently with a subset of instructions more resembling a typical "RISC" instruction set.
  More results at FactBites »

 
 

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