dict.org

The DICT Development Group


Search for:
Search type:
Database:

Database copyright information
Server information
Wiki: Resources, links, and other information


2 definitions found
 for complex instruction set computer
From WordNet (r) 3.0 (2006) :

  complex instruction set computer
      n 1: (computer science) a kind of computer architecture that has
           a large number of instructions hard coded into the CPU chip
           [syn: complex instruction set computing, complex
           instruction set computer, CISC] [ant: RISC, reduced
           instruction set computer, reduced instruction set
           computing]

From The Free On-line Dictionary of Computing (18 March 2015) :

  Complex Instruction Set Computer
  CISC
  
     (CISC) A processor where each instruction can perform several
     low-level operations such as memory access, arithmetic
     operations or address calculations.  The term was coined in
     contrast to Reduced Instruction Set Computer.
  
     Before the first RISC processors were designed, many computer
     architects were trying to bridge the "{semantic gap" - to
     design instruction sets to support high-level 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 compiled into single
     instructions.
  
     While these architectures 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 the 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 an instruction, both in execution time and silicon
     area.  This is particularly true for processors which used
     microcode to decode the (macro) instruction.  It is easier
     to debug a complex instruction set implemented in microcode
     than one whose decoding is "{hard-wired" in silicon.
  
     Examples of CISC processors are the Motorola 680x0 family
     and the Intel 80186 through Intel 486 and Pentium.
  
     (1994-10-10)
  

Questions or comments about this site? Contact webmaster@dict.org