Bell's law of computer classes

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Bell's law of computer classes[1] formulated by Gordon Bell in 1972[2] describes how types of computing systems (referred to as computer classes) form, evolve and may eventually die out. New classes create new applications resulting in new markets and new industries.

Bell considers the law to be partially a corollary to Moore's law which states "the number of transistors per chip double every 24 months". Unlike Moore's law, a new computer class is usually based on lower cost components that have fewer transistors or less bits on a magnetic surface, etc. A new class forms about every decade. It also takes up to a decade to understand how the class formed, evolved, and is likely to continue. Once formed, a lower priced class may evolve in performance to take over and disrupt an existing class. This evolution has caused clusters of scalable personal computers with 1 to thousands of computers to span a price and performance range of use from a PC, through mainframes, to become the largest supercomputers of the day. Scalable clusters became a universal class beginning in the mid-1990s; by 2010, clusters of at least one million independent computers will constitute the world's largest cluster.

Definition: Roughly every decade a new, lower priced computer class forms based on a new programming platform, network, and interface resulting in new usage and the establishment of a new industry.

Established market class computers aka platforms are introduced and continue to evolve at roughly a constant price (subject to learning curve cost reduction) with increasing functionality (or performance) based on Moore's law that gives more transistors per chip, more bits per unit area, or increased functionality per system. Roughly every decade, technology advances in semiconductors, storage, networks, and interfaces enable a new, lower cost computer class aka platform to form to serve a new need that is enabled by smaller devices e.g. less transistors per chip, less expensive storage, displays, i/o, network, and unique interface to people or some other information processing sink or source. Each new lower priced class is then established and maintained as a quasi independent industry and market. Such a class is likely to evolve to substitute for an existing class or classes as described above with computer clusters.

Computer classes that conform to the law[edit]

Beginning in the 1990s, a single class of scalable computers or mega-servers, (built from clusters of a few to tens of thousands of commodity microcomputer-storage-networked bricks), began to cover and replace mainframes, minis, and workstations to become the largest computers of the day, and when applied for scientific calculation they are commonly called a supercomputer.[6]


Bell's law of computer classes and class formation was first mentioned in 1970 with the introduction of the Digital Equipment PDP-11 mini to differentiate it from mainframes and the potentially emerging micros. The law was described in 1972 by Gordon Bell. The emergence and observation of a new, lower-priced microcomputer class based on the microprocessor stimulated the creation of the law that Bell described in articles and Bell's books.

Other computer industry laws[edit]

See also the several laws (e.g. Moore's law, Metcalfe's law) that describe and govern the computer industry.[7]


  1. ^ Bell, G., "Bell's Law for the Birth and Death of Computer Classes", Communications of the ACM, January 2008, Vol 51, No. 1, pp 86–94.
  2. ^ Bell, C. G., R. Chen and S. Rege, "The Effect of Technology on Near Term Computer Structures" Computer 2 (5) 29-38 (March/April 1972) plots various mainframe and emerging minicomputer by function and price.
  3. ^ Bell, C. G., "The Mini and Micro Industries", Computer (17) no. 10, pp. 14–30 (October 1984) gives the evolution of these industries including the rise to 91 minicomputer companies and decline to six, of which only three live in 2005.
  4. ^ Bell, C. Gordon "Rise and Fall of Minicomputers" IEEE Global History Network, STARS (22 January 2013)
  5. ^ Fojik, Kim, Chen, Lin, Fick, Park, Seok, Chen, Foo, Blauw and Sylvester :A millimeter-Scale Energy-Autonomous Sensor System With Stacked Battery and Solar Cells", IEEE JSSC Vol. 48, No.3. March 2013, pp. 801-813.
  6. ^ Bell, G. "Bell's Law", Microsoft Research Technical Report. MSR-2007-TR-146 Bells Law.
  7. ^ Bell, C. Gordon, John E. McNamara, High Tech Ventures: The Guide to Entrepreneurial Success, Addison-Wesley, 1991, provides the best description of technology progress including Moore's law as applied to the creation of new classes that result in establishing new industries.