Topic: what is a computer

topics > Group: computer science

machine model
philosophy of mathematics

computer as an intelligent agent
computer as state machine
discrete vs. continuous
hardware vs. software
history of computers
history of programming
intelligent machines
metaphysics and epistemology
mathematics as a formal system
non-deterministic processing
people vs. computers
pointer machines
physics as computation
programming as mathematics
reality is a machine
sensitivity of software to change
thought is computational
Turing machine
using a computer as a communication/information medium
von Neumann computer
what is a number


A computer is device that executes a simple set of instructions, rapidly, repetitively, and exactly. As a friend of Shannon's said, a program is written in words of one microsyllable.

A computer stores its program internally. This greatly increases the speed of execution and allows rapid, non-sequential processing of the program and data.

Given sufficient storage and time, a computer can implement any computable function. By interpreting the numbers appropriately, the computer can simulate other media. In this way a computer is the universal machine.

So the other representation of a computer is as a symbol processor. This was the motivation of Leibnitz and Boole. By manipulating symbols, a machine could simulate thought and even do a better, more accurate job of it than man. This view is prevalent in computer science as well. A symbolic processor has a formal representation that appears to capture the essence of a program better than a long sequence of detailed instructions obviously removed from the purpose of those instructions. (cbb 4/94)

Subtopic: artifacts up

Quote: artifacts are regular and repetitive; reflect the purpose of their creator [»monoJ_1971]
Quote: Aristotle: could do without subordinates if inanimate instruments could do their own work by command or intelligent anticipation [»aris_322]

Subtopic: algorithm up

Quote: Pingala (before 200 B.C.) gives an algorithm for computing the total number of arrangements of two things in n places

Subtopic: computer as symbolic, formal system up

Quote: computers are for manipulating symbols
Quote: computer programs are formal (syntactic); they manipulate symbols through precisely stated rules; abstract, manipulated without meaning [»searJR1_1990]
Quote: Leibniz developed the idea of a formal system as a means to knowledge, and the possibility of transforming a formal system into a real machine [»kramS2_1996]
Quote: Leibniz invented first calculating machine; for manipulating concepts
Quote: with symbolic logic, the process of inference is precise, almost mechanical
Quote: to interpret the semantics of computer behavior must see it as operating on symbols [»pylyZW_1986]
Quote: computing science may provide symbolic calculation that is better than human reasoning; Leibniz's dream [»dijkEW12_1989]
Quote: the essence of change in a computational system is the appearance and disappearance of tokens of external symbols [»kentW6_1991]

Subtopic: computer as universal up

Quote: a computer is a universal medium in that it can simulate any other medium [»kayA3_1977]
Quote: computer hardware can execute almost any sequence of instructions; the secret of its power, flexibility, simplicity, and reliability
Quote: the Jacquard loom could weave any imaginable design; basis for Babbage's analytical engine
Quote: Babbage's analytical engine could compute any formula that consisted of operations on variables and conditional modifications [»babbC_1864, OK]
Quote: Babbage substituted unbounded time for unbounded space; allows a finite machine to make calculations of an unlimited extent [»babbC_1864, OK]
Quote: the cards for the Analytical Engine may contain errors; but once developed, they are valid for an infinite number of particular cases [»menaLF10_1842, OK]
Quote: with a universal Turing machine, you can program it for each different job [»turiAM9_1947]

Subtopic: computer as number up

Quote: the computable sequences are enumerable because of the many-one relationship between Turing machine numbers and computable sequences [»turiAM11_1936]

Subtopic: modifying programs up

Quote: a program can be modified by computation; as long as this wire is not connected, the computer is easy to access and control [»zuseK_1984]
Quote: by modifying instructions; EDVAC-type machines can carry out processes that would otherwise require vast programs
Quote: instruction modification is more important than subsequences; allows a short program to carry out a very long sequence of instructions

Subtopic: computer as rules up

Quote: logical computing machines can do anything described as 'rule of thumb' or 'purely mechanical'; other constructions are mathematically equivalent [»turiAM9_1947]
Quote: computing is forming new data from given data according to a rule [»zuseK_1984]
Quote: computers carry out any definite rule of thumb process that a human could do in a disciplined but unintelligent manner [»turiA3_1951]
Quote: computers are like a human with a desk calculator and paper obeying explicit instructions
Quote: if you can think of a method using pencil and paper, you can usually implement it by machine [»turiA3_1951]
Quote: computers don't follow rules, they only act as if they did [»searJR_1984]

Subtopic: computer as instructions up

Quote: programming is controlling the activity of a digital computer by expressing one's will on punched tapes and other input medium [»turiA3_1951]
Quote: the Analytical Engine can not originate anything. It can do whatever we know how to order it to perform. It can not anticipate analytical relations or truths [»menaLF10_1842, OK]
Quote: the transition function is 'obeying an instruction'
Quote: use check sheets to verify a routine experimentally; step through the routine, recording all details [»turiA3_1951]
Quote: the sequence control unit reads 24-bit commands (move A to B and start C) from a perforated paper tape [»compHU_1946]

Subtopic: complex behavior from simple instructions up

Quote: the real mystique of computers is their elaborate behavior from limited capabilities [»kentW_1978]
Quote: a computer can perform only the basic operations of arithmetic
Quote: with a computer, the simplest mathematical calculation requires an extended sequence of orders [»wilkMV_1951]
Quote: computers have applications in matrix operations, differential equations, logical problems including chess and draughts, commercial and industrial subjects, fault diagnosis, programming, and pure mathematics [»ferr8_1952]
Quote: a computer program must be written in words of one microsyllable
Quote: we attach meaning to perceived structures in the meaningless bits of computer memory and the meaningless traces of computer programs [»dijkEW2_1971]

Subtopic: computer as stored programs up

Quote: a computer is all purpose because it executes stored programs of instructions
Quote: the purpose of a computer is to execute our programs, not vice versa [»dijkEW3_1976]
Quote: use the same memory for both orders and numbers by expressing orders in a numerical code; from von Neumann's report [»wilkMV_1951]

Subtopic: computer as memory up

Quote: memory is a characteristic feature of computers; the act of inserting an item erases whatever was there before [»straC8_1967]
Quote: a location or L-value is an area of the store that has a content or R-value; change the R-value with an updating operation [»straC8_1967]

Subtopic: computer as state machine up

Quote: the state of the machine at one prepulse is completely determined by its state at the previous one; consists of electronic store, accumulator, and instruction number [»turiA3_1951]
Quote: programming is not interested in the state of the machine at every moment; only at prepulses
Quote: need conventions to reduce uncertainty about a machine's state; computers have very great flexibility [»turiA3_1951]

Subtopic: programs as ultra-detailed up

Quote: a program is a sequence of orders for performing a calculation; unlike a human, every contingency must be foreseen [»wilkMV_1951]
Quote: a computer is a device that automatically executes exhaustively, detailed instructions for complex calculations [»vonnJ6_1945]
Quote: computers can only do tasks which people have broken into very small steps; people do not know how to turn many tasks into steps; e.g., recognition, common sense, solving a problem [»millHD9_1982]
Quote: a computer program must be written in words of one microsyllable
Quote: a program is an elaborate formulae for some formal system; made concrete by a computer [»dijkEW12_1989]
Quote: a vast amount of code is required to realize a programmer's intent, often concisely stated [»laruJR5_2004]

Subtopic: computer as fast and reliable up

Quote: a computer must function faultlessly; humans may recognize and correct faults, or this may be done automatically [»vonnJ6_1945]
Quote: computers can perform arithmetic operations exceedingly rapidly, remember a great many numbers, and make decisions on intermediate results [»ferr8_1952]
Quote: Manchester "baby" computer correctly ran 3.5 million operations in 52 minutes

Subtopic: von Neumann computer up

Quote: a computer consists of memory, an arithmetical unit, input and output mechanisms, and a control unit
Quote: the magnetic store is divided into tracks; each half-track is loaded into a page of memory; each page, a cathode ray tube, contains 64 lines of 20 binary digits each [»turiA3_1951]
Quote: practical computing machines dial the position of information in a store; delay of a few microseconds; most are universal [»turiAM9_1947]
Quote: EDVAC-type machines have internal memory, elementary instructions stored as data; stands for Electronic Discrete Variable Arithmetic Computer [»maucJW1_1947]

Subtopic: limits of computers up

Quote: physical limitations bound the number of steps in a computation; about 10^20 steps and 10^20 memory elements [»turiAM9_1947]
Quote: computers do not guarantee absence of hardware faults; breaks proof of soundness of link-time type-checking; e.g., cosmic rays or heat-induced faults

Related Topics up

Group: formalism   (9 topics, 478 quotes)
Group: information   (46 topics, 1160 quotes)
Group: machine model   (13 topics, 206 quotes)
Group: philosophy of mathematics   (11 topics, 330 quotes)
Group: systems   (17 topics, 530 quotes)

Topic: computer as an intelligent agent (49 items)
Topic: computer as state machine (20 items)
Topic: discrete vs. continuous (47 items)
Topic: hardware vs. software (15 items)
Topic: history of computers (66 items)
Topic: history of programming (91 items)
Topic: intelligent machines (28 items)
Topic: metaphysics and epistemology (99 items)
Topic: mathematics as a formal system (30 items)
Topic: non-deterministic processing (19 items)
Topic: people vs. computers (55 items)
Topic: pointer machines (17 items)
Topic: physics as computation (31 items)
Topic: programming as mathematics (27 items)
Topic: reality is a machine (48 items)
Topic: rules (43 items)
Topic: sensitivity of software to change (44 items)
Topic: thought is computational (60 items)
Topic: Turing machine (30 items)
Topic: using a computer as a communication/information medium (32 items)
Topic: von Neumann computer (14 items)
Topic: what is a number
(55 items)

Updated barberCB 7/05
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Thesa is a trademark of C. Bradford Barber.