World Library  
Flag as Inappropriate
Email this Article

Minimal instruction set computer

Article Id: WHEBN0003620266
Reproduction Date:

Title: Minimal instruction set computer  
Author: World Heritage Encyclopedia
Language: English
Subject: Reduced instruction set computing, Instruction set, History of general-purpose CPUs, Central processing unit, Complex instruction set computing
Collection: Central Processing Unit, Instruction Processing
Publisher: World Heritage Encyclopedia

Minimal instruction set computer

Generic 4-stage pipeline; the colored boxes represent instructions independent of each other
(Not to be confused with multiple instruction set computer, also abbreviated MISC, such as the HLH Orion or the OROCHI VLIW processor.)

Minimal Instruction Set Computer (MISC) is a processor architecture with a very small number of basic operations and corresponding opcodes. Such instruction sets are commonly stack-based rather than register-based to reduce the size of operand specifiers.

Such a stack machine architecture is inherently simpler since all instructions operate on the top-most stack entries.

As a result of the stack architecture is an overall smaller instruction set, a smaller and faster instruction decode unit with overall faster operation of individual instructions.

Separate from the stack definition of a MISC architecture, is the MISC architecture being defined with respect to the number of instructions supported.

  • Typically a Minimal Instruction Set Computer is viewed as having 32 or fewer instructions,[1][2][3] where NOP, RESET and CPUID type instructions are generally not counted by consensus due to their fundamental nature.
  • 32 instructions is viewed as the highest allowable number of instructions for a MISC, as 16 or 8 instructions are closer to what is meant by "Minimal Instructions".
  • A MISC CPU cannot have zero instructions as that is a zero instruction set computer.
  • A MISC CPU cannot have one instruction as that is a one instruction set computer[4]
  • The implemented CPU instructions should by default not support a wide set of inputs, so this typically means an 8-bit or 16-bit CPU.
  • If a CPU has an NX bit, it is more likely to be viewed as being CISC or RISC.
  • MISC chips typically don't have hardware memory protection of any kind unless there is an application specific reason to have the feature.
  • If a CPU has a microcode subsystem, that excludes it from being a MISC system.
  • The only addressing mode considered acceptable for a MISC CPU to have is LOAD-STORE, the same as for RISC CPUs.
  • MISC CPUs can typically have between 64 KB to 4 GB of accessible addressable memory—but most MISC designs are under 1 megabyte.

Also, the instruction pipelines of MISC as a rule tend to be very simple. Instruction pipelines, branch prediction, out-of-order execution, register renaming and speculative execution broadly exclude a CPU from being classified as a MISC architecture system.


  • History 1
  • Design weaknesses 2
  • Notable CPUs 3
  • See also 4
  • References 5
  • External links 6


Some of the first digital computers implemented with instruction sets were by modern definition Minimal Instruction Set computers.

Among these various computers, only ILLIAC and ORDVAC had compatible instruction sets.

  • Manchester Small-Scale Experimental Machine (SSEM), nicknamed "Baby" (University of Manchester, England) made its first successful run of a stored-program on June 21, 1948.
  • EDSAC (University of Cambridge, England) was the first practical stored-program electronic computer (May 1949)
  • Manchester Mark 1 (University of Manchester, England) Developed from the SSEM (June 1949)
  • Council for Scientific and Industrial Research) Australia (November 1949)
  • EDVAC (Ballistic Research Laboratory, Computing Laboratory at Aberdeen Proving Ground 1951)
  • ORDVAC (U-Illinois) at Aberdeen Proving Ground, Maryland (completed November 1951)[5]
  • IAS machine at Princeton University (January 1952)
  • MANIAC I at Los Alamos Scientific Laboratory (March 1952)
  • ILLIAC at the University of Illinois, (September 1952)

Early stored-program computers

  • The IBM SSEC had the ability to treat instructions as data, and was publicly demonstrated on January 27, 1948. This ability was claimed in a US patent.[6] However it was partially electromechanical, not fully electronic. In practice, instructions were read from paper tape due to its limited memory.[7]
  • The Manchester SSEM (the Baby) was the first fully electronic computer to run a stored program. It ran a factoring program for 52 minutes on June 21, 1948, after running a simple division program and a program to show that two numbers were relatively prime.
  • The ENIAC was modified to run as a primitive read-only stored-program computer (using the Function Tables for program ROM) and was demonstrated as such on September 16, 1948, running a program by Adele Goldstine for von Neumann.
  • The BINAC ran some test programs in February, March, and April 1949, although was not completed until September 1949.
  • The Manchester Mark 1 developed from the SSEM project. An intermediate version of the Mark 1 was available to run programs in April 1949, but was not completed until October 1949.
  • The EDSAC ran its first program on May 6, 1949.
  • The EDVAC was delivered in August 1949, but it had problems that kept it from being put into regular operation until 1951.
  • The CSIR Mk I ran its first program in November 1949.
  • The SEAC was demonstrated in April 1950.
  • The Pilot ACE ran its first program on May 10, 1950 and was demonstrated in December 1950.
  • The SWAC was completed in July 1950.
  • The Whirlwind was completed in December 1950 and was in actual use in April 1951.
  • The first ERA Atlas (later the commercial ERA 1101/UNIVAC 1101) was installed in December 1950.

Design weaknesses

The disadvantage of an MISC is that instructions tend to have more sequential dependencies, reducing overall instruction-level parallelism.

MISC architectures have much in common with the Forth programming language and the Java Virtual Machine that are weak in providing full instruction-level parallelism.

Notable CPUs

Probably the most commercially successful MISC was the original INMOS transputer archecture that had no floating-point unit. However, many eight-bit microcontrollers (for embedded computer applications) fit into this category.

Each STEREO spacecraft includes two P24 MISC CPUs and two CPU24 MISC CPUs.[8][9]

See also


  1. ^ Chen-hanson Ting and Charles H. Moore. "MuP21--A High Performance MISC Processor". 1995.
  2. ^ Michael A. Baxter. "Minimal instruction set computer architecture and multiple instruction issue method". 1993.
  3. ^ Richard Halverson, Jr. and Art Lew. "An FPGA-Based Minimal Instruction Set Computer". 1995. p. 23.
  4. ^ Kong, J.H.; Ang, L.-M.; Seng, K.P. "Minimal Instruction Set AES Processor using Harvard Architecture". 2010. doi:10.1109/ICCSIT.2010.5564522
  5. ^ James E. Robertson (1955), Illiac Design Techniques, report number UIUCDCS-R-1955-146, Digital Computer Laboratory, University of Illinois at Urbana-Champaign 
  6. ^ F.E. Hamilton, R.R. Seeber, R.A. Rowley, and E.S. Hughes (January 19, 1949). "Selective Sequence Electronic Calculator". US Patent 2,636,672. Retrieved April 28, 2011.  Issued April 28, 1953.
  7. ^  
  8. ^ R. A. Mewaldt, C. M. S. Cohen, W. R. Cook, A. C. Cummings, et. al. "The Low-Energy Telescope (LET) and SEP Central Electronics for the STEREO Mission".
  9. ^ C.T. Russell. "The STEREO Mission". 2008.

External links

This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.