Complex Instruction Set Computer

Complex Instruction Set Computers (usually abbreviated to CISC) is a school of CPU architecture which was the default approach until the rise of the Reduced Instruction Set Computer approach.

CISC dates to the period when computers were usually programmed in assembly language, so the design was to some extent biased toward making the programmer's life easier. So it included instructions which 'did more', so that the programmer would have to write fewer lines of source code.

Another way of looking at CISC, especially in its later years, is that it tried to maximize the instruction density - i.e. the number of memory bits needed to hold a given set of programming functionality. This maximizee the efficiency of the main memory's bandwidth - the latter having been the principle bottleneck in older computers (particularly those using core memory).