Computer Architecture
The Anatomy of Modern Processors

Classification of Single Processors

Historical Trends

Era Style Hardware Software
pre 1970 RISC Simple Assembly language
~ 1970 - ~2000 CISC Complex
  • Designed to simplify compiler's task
 High Level Languages
  • FORTRAN
  • Algol
  • Pascal
  • C
~ 1980 - RISC Simple
  • Designed to run as fast as possible
 High Level Languages
  • FORTRAN
  • Pascal
  • C
Optimising Compilers needed!
2000 - RISC/
VLIW?		 Simple
  • Designed to run as fast as possible
  • Multiple instructions in parallel
 High Level Languages
  • FORTRAN
  • Pascal
  • C
  • Java
Optimising Compilers required!

Complex Instruction Set Computers (CISC)

As high level languages started to become popular, so computer architects attempted to make the machine's capabilities match constructs used by programmers. As an example, complex addressing modes were added so that an expression like: 
x = a[j++];
could be transformed to a single machine instruction.

At that time, memory was relatively expensive and slow, so that compacting a program into as few instructions as possible was seen as a desirable goal. Smaller programs meant that they loaded faster and that more (scarce and expensive) memory was available for data.

Significant CISC architectures

IBM 360, 370 An extensive family of mainframe processors were designed and manufactured in this series
DEC PDP-11 At one time the most popular minicomputer family
DEC VAX DEC's successor to its PDP-11 family - one of the first 32-bit machines
Intel x86 Starting with the 8088 which powered the first IBM PCs, the x86 architecture has developed with the popularity of PCs
Motorola 68K A family of 32-bit processors - used in early Apple Macintoshes and extensively in embedded systems

    Additional References

    Continue on to RISC processors Back to the Table of Contents
    © John Morris, 1999

    e-REdING. Biblioteca de la Escuela Superior de Ingenieros de Sevilla.


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