Notes on Computer

Notes

1. ^ In 1946, ENIAC required an estimated 174 kW. By comparison, a modern laptop computer may use around 30 W; nearly six thousand times less. "Approximate Desktop & Notebook Power Usage". University of Pennsylvania. http://www.upenn.edu/computing/provider/docs/hardware/powerusage.html. Retrieved on 2009-06-20.
2. ^ Early computers such as Colossus and ENIAC were able to process between 5 and 100 operations per second. A modern "commodity" microprocessor (as of 2007) can process billions of operations per second, and many of these operations are more complicated and useful than early computer operations. {{cite web |url=http://www.intel.com/cd/channel/reseller/asmo-na/eng/products/mobile/processors/core2duo_m/feature/index.htm |title=Intel® Core™2 Duo Mobile Processor: Features |publisher=Intel Corporation |accessdate=2009-06-20
3. ^ computer, n., Oxford English Dictionary (2 ed.), Oxford University Press, 1989, http://dictionary.oed.com/, retrieved on 2009-04-10
4. ^ "Heron of Alexandria". http://www.mlahanas.de/Greeks/HeronAlexandria2.htm. Retrieved on 2008-01-15.
5. ^ ^{a b} Ancient Discoveries, Episode 11: Ancient Robots, History Channel, http://www.youtube.com/watch?v=rxjbaQl0ad8, retrieved on 2008-09-06
6. ^ Howard R. Turner (1997), Science in Medieval Islam: An Illustrated Introduction, p. 184, University of Texas Press, ISBN 0-292-78149-0
7. ^ Donald Routledge Hill, "Mechanical Engineering in the Medieval Near East", Scientific American, May 1991, pp. 64-9 (cf. Donald Routledge Hill, Mechanical Engineering)
8. ^ The analytical engine should not be confused with Babbage's difference engine which was a non-programmable mechanical calculator.
9. ^ Columbia University Computing History: Herman Hollerith
10. ^ http://www.time.com/time/time100/scientist/profile/turing.html
11. ^ "Inventor Profile: George R. Stibitz". National Inventors Hall of Fame Foundation, Inc.. http://www.invent.org/hall_of_fame/140.html.
12. ^ B. Jack Copeland, ed., Colossus: The Secrets of Bletchley Park's Codebreaking Computers, Oxford University Press, 2006
13. ^ Lavington 1998, p. 37
14. ^ This program was written similarly to those for the PDP-11 minicomputer and shows some typical things a computer can do. All the text after the semicolons are comments for the benefit of human readers. These have no significance to the computer and are ignored. (Digital Equipment Corporation 1972)
15. ^ Attempts are often made to create programs that can overcome this fundamental limitation of computers. Software that mimics learning and adaptation is part of artificial intelligence.
16. ^ It is not universally true that bugs are solely due to programmer oversight. Computer hardware may fail or may itself have a fundamental problem that produces unexpected results in certain situations. For instance, the Pentium FDIV bug caused some Intel microprocessors in the early 1990s to produce inaccurate results for certain floating point division operations. This was caused by a flaw in the microprocessor design and resulted in a partial recall of the affected devices.
17. ^ Even some later computers were commonly programmed directly in machine code. Some minicomputers like the DEC PDP-8 could be programmed directly from a panel of switches. However, this method was usually used only as part of the booting process. Most modern computers boot entirely automatically by reading a boot program from some non-volatile memory.
18. ^ However, there is sometimes some form of machine language compatibility between different computers. An x86-64 compatible microprocessor like the AMD Athlon 64 is able to run most of the same programs that an Intel Core 2 microprocessor can, as well as programs designed for earlier microprocessors like the Intel Pentiums and Intel 80486. This contrasts with very early commercial computers, which were often one-of-a-kind and totally incompatible with other computers.
19. ^ High level languages are also often interpreted rather than compiled. Interpreted languages are translated into machine code on the fly by another program called an interpreter.
20. ^ The control unit's role in interpreting instructions has varied somewhat in the past. Although the control unit is solely responsible for instruction interpretation in most modern computers, this is not always the case. Many computers include some instructions that may only be partially interpreted by the control system and partially interpreted by another device. This is especially the case with specialized computing hardware that may be partially self-contained. For example, EDVAC, one of the earliest stored-program computers, used a central control unit that only interpreted four instructions. All of the arithmetic-related instructions were passed on to its arithmetic unit and further decoded there.
21. ^ Instructions often occupy more than one memory address, so the program counters usually increases by the number of memory locations required to store one instruction.
22. ^ David J. Eck (2000). The Most Complex Machine: A Survey of Computers and Computing. A K Peters, Ltd.. p. 54. ISBN 9781568811284.
23. ^ Erricos John Kontoghiorghes (2006). Handbook of Parallel Computing and Statistics. CRC Press. p. 45. ISBN 9780824740672.
24. ^ Flash memory also may only be rewritten a limited number of times before wearing out, making it less useful for heavy random access usage. (Verma 1988)
25. ^ Donald Eadie (1968). Introduction to the Basic Computer. Prentice-Hall. p. 12.
26. ^ Arpad Barna; Dan I. Porat (1976). Introduction to Microcomputers and the Microprocessors. Wiley. p. 85. ISBN 9780471050513.
27. ^ Jerry Peek; Grace Todino, John Strang (2002). Learning the UNIX Operating System: A Concise Guide for the New User. O'Reilly. p. 130. ISBN 9780596002619.
28. ^ Gillian M. Davis (2002). Noise Reduction in Speech Applications. CRC Press. p. 111. ISBN 9780849309496.
29. ^ However, it is also very common to construct supercomputers out of many pieces of cheap commodity hardware; usually individual computers connected by networks. These so-called computer clusters can often provide supercomputer performance at a much lower cost than customized designs. While custom architectures are still used for most of the most powerful supercomputers, there has been a proliferation of cluster computers in recent years. (TOP500 2006)
30. ^ Agatha C. Hughes (2000). Systems, Experts, and Computers. MIT Press. p. 161. ISBN 9780262082853. "The experience of SAGE helped make possible the first truly large-scale commercial real-time network: the SABRE computerized airline reservations system..."
31. ^ "A Brief History of the Internet". Internet Society. http://www.isoc.org/internet/history/brief.shtml. Retrieved on 2008-09-20.
32. ^ Most major 64-bit instruction set architectures are extensions of earlier designs. All of the architectures listed in this table, except for Alpha, existed in 32-bit forms before their 64-bit incarnations were introduced.