Computer clusters

Bell's Law of Computer Classes

Bell's Law of Computer Classes formulated by Gordon Bell in 1972 describes how 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.

Bell's Law of Computer Classes

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.

Computers classes that have formed based on Bell's Law

As of 2005, the computer classes include:

  • mainframes (1960s)
  • minicomputers (1970s)
  • personal computers and workstations evolving into a network enabled by Local Area Networking or Ethernet (1980s)
  • web browser client-server structures enabled by the Internet (1990s)
  • web services, e.g. Microsoft's .NET (2000s) or the Grid
  • small form-factor devices such as cell phones and other cell phone sized devices (CPSD), e.g. BlackBerries, iPods, Smartphones, and Trēos (c. 2000)
  • Wireless Sensor Networks, aka motes (c. >2005)

Bell predicts that home and body area networks will form by 2010.

As of 2005, Bell believes i.e. is betting that CPSDs will form a dominant computer class or platform measured by units and revenue. These evolve from the phone and PDA functions to include new "killer applications" yet to be determined. Furthermore, CPSDs will substitute for many PC's functions (e.g. email, web browsing). Use will evolve, with or without attachments (e.g. keyboards, displays for document creation, presentations), to include almost all of the PC's functions except large file stores for video content.

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, or what is commonly called a supercomputer.

History of Bell's Law of Computer Classes

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


  • Bell, C. G., R. Cady, H. McFarland, B. Delagi, J. O'Laughlin, R. Noonan and W. Wulf, "A New Architecture for Mini-Computers -- The DEC PDP-11", Sprint Joint Computer Conference, pp. 657-675 (1970) is the first use of the law to describe and forecast the evolution of mainframe, mini, and inevitable micro computer.
  • 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.
  • Bell, C. G., "The Mini and Micro Industries", Computer (17) no. 10, pp. 14-30 (October 1984) gives th evolution of these industries including the rise to 91 minicomputer companies and decline to six, of which only three live in 2005.
  • 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.
  • 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.
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