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         Glossary of Computer Engineering and Programming Terminology
                (Partial list from BRL Report 1115, March 1961)


Access to storage under conditions in which the next position from which information is to be obtained is in no way dependent on the previous one.


(1) The time interval between the instant at which information is: (a) called for from storage and the instant at which delivery is completed, i.e., the read time; or (b) ready for storage and the instant at which storage is completed, i.e., the write time. (2) the latency plus the word-time.


Freedom from error. Accuracy contrasts with precision; e.g., a four- place table, correctly computed, is accurate; a six-place table containing an error is more precise, but not accurate.


A device capable of forming the sum of two or more quantities.


A label such as an integer or other set of characters which identifies a register, location of device in which information is stored.


The representation of numerical quantities by means of physical variables, e.g., translation, rotation, voltage, resistance; contrasted with "digital."


An analog computer designed and used primarily for solving many types of differential equations.


A logical operator which has the property such that if P and Q are two statements, then the statement "P and Q" is true or false precisely according to the following table of possible combinations:

        P                Q                 P and Q
     False  0        False   0            False   0
     False  0        True   11            False   0
     True   1        False   0            False   0
     True   1        True    1            True    1

The "and" operator is often represented by a centered dot (.), or by no sign, as in P. Q or PQ; the term conjunction is applied to this operator.


A signal circuit with two or more input wires which has the property that the output wire gives a signal if and only if all input wires receive coincident signals. ARITHMETIC UNIT That portion of the "hardware" of an automatic computer in which the arithmetic and logical operations are performed.


The entire field of investigation, design, development, application, and methods of rendering or making processes or machines self-acting or self- moving; rendering automatic; theory, art or technique of making a device, machine, process or procedure more fully automatic; the implementation of a self-acting or self-moving, hence, automatic process or machine.


A characteristic or property involving a selection, choice or condition in which there are but two possible alternatives.


A single digit or group of characters or symbols representing the total, aggregate or amount of units utilizing the base two; usually using only the digits "0" and "1" to express quantity.


The upper and lower limits of the numbers which may be processed in a computer register, e.g., in the accumulator, e.g., the capacity of a computer may be ten decimal digits or the capacity of a computer may be +.00000 00001 to +.99999 99999. Quantities which exceed the capacity usually interrupt the operation of the computer in some fashion; the quantity of information which may be stored in a storage unit; see Capacity, Storage.


Maximum number of words or characters which a device is capable of storing; a measure of the ability of a device to store information for future reference.


One of a set of elementary symbols such as those corresponding to the keys on a typewriter. The symbols usually include the decimal digits 0 through 9, the letters A through Z, punctuation marks, operation symbols, and any other single symbols which a computer may read, store, or write; a pulse code representation of such a symbol.


A means of verification of information or operation during or after an operation.


A system of symbols or their use in representing rules for handling the flow or processing of information; to actually prepare problems for solution on a specific computer.


The list, in computer code or in pseudo-code, of the successive computer operations required to solve a given problem; repertoire of instructions. CODING, ALPHABETIC A system of abbreviation used in preparing information for input into a computer such that information is reported in the form of letters, e.g., New York as NY, carriage return as CN, etc.


Any technique in which a computer is used to help bridge the gap between some "easiest" form, intellectually and manually, of describing the steps to be followed in solving a given problem and some "most efficient" final coding of the same problem for a given computer; two basic forms are Routine, Compilation and Routine, interpretation.


A system of abbreviation used in the preparation of information for machine acceptance by reducing all information to numerical quantities; in contrast to alphabetic coding.


A pulse, signal, or set of signals initiating one step in the performance of a computer operation; that portion of the instruction word which specifies the operation to be performed; see instruction.


Any device capable of accepting information, applying prescribed processes to the information, and supplying the results of these processes; sometimes, more specifically, a device for performing sequences of arithmetic and logical operations; sometimes, still more specifically, a stored-program digital computer capable of performing sequences of internally-stored instructions, as opposed to calculators on which the sequence is impressed manually (desk calculator) or from tape or cards (card programmed calculator).


A calculating machine which solves problems by translating physical conditions like flow, temperature or pressure into electrical quantities and using electrical equivalent circuits for the physical phenomenon.


A calculating device in which an operation is initiated by a signal generated upon completion of a previous operation; contrasted with Synchronous Computer.


A calculating device which handles long sequences of operations without human intervention.


A calculating device utilizing numbers to express all the variables and quantities of a problem. The numbers are usually expressed as a space-time distribution of punched holes, electrical pulses, sonic pulses, etc.


A calculating device in which the performance of all operations is controlled with periodic signals from a master clock.


(1) Usually, those parts of a digital computer which effect the carrying out of instructions in proper sequence, the interpretation of each instruction, and the application of the proper signals to the arithmetic unit and other parts in accordance with this interpretation. (2) Frequently, one or more of the components in any mechanism responsible for interpreting and carrying out manually-initiated directions. Sometimes called manual control. (3) In some applications of mathematics, a mathematical check.


That portion of the hardware of an automatic digital computer which directs the sequence of operations, interprets the coded instructions, and initiates the proper commands to the computer circuits to execute the instructions.


A magnetic material capable of assuming and remaining at one of two or more conditions of magnetization, thus capable of providing storage, gating or switching functions, usually of toroidal shape and pulsed or polarized by electric currents carried on wire adjacent the material.


The art or process of transforming masses of raw test or experimentally obtained data, usually gathered by instrumentation, into useful, ordered, or simplified intelligence.


To ascertain the intended meaning of the individual characters or groups of characters in the pseudo-coded program.


One of the n symbols of integral value ranging from 0 to n-1 inclusive in a scale of numbering of base n, e.g., one of the ten decimal digits, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.


A whole number in the binary scale of notation; this digit may be only 0 (zero) or 1 (one). It may be equivalent to an "on" or "off" condition, a "yes" or a "no," etc.


The quality of utilizing numbers in a given scale of notation to represent all the quantities that occur in a problem or a calculation.


The period during which a computer is malfunctioning or not operating correctly due to machine failures; contrasted with available time, idle time or standby time. Scheduled maintenance time is also considered down-time, in as much as the computer is unable to operate during this period.


A rotating cylinder on whose magnetic-material coating information is stored in the form of magnetized dipoles, the orientation or polarity of which is used to store binary information.


Pertaining to the application of that branch of science which deals with the motion, emission, and behavior of currents of free electrons, especially in vacuum, gas or phototubes and special conductors or semi-conductors. Contrasted with electric which pertains to the flow of large currents in wires or conventional conductors.


The amount of loss of precision in a quantity; the difference between an accurate quantity and its calculated approximation; errors occur in numerical methods, e.g., an error introduced by the truncation of a power series defining a transcendental function. This may be classified as an error introduced by the numerical method, there is no mistake involved and the computer is operating properly; mistakes occur in programming, coding, data transcription, and operating, thus, usually humans make mistakes, e.g., assigning a wrong address when coding a problem; malfunctions occur in computers and are due to physical limitations on the properties of materials. An error is sometimes considered to be the differential margin by which a controlled unit deviates from its target value.


A bi-stable device; a device capable of assuming two stable states; a bi-stable device which may assume a given stable state depending upon the pulse history of one or more input points and having one or more output points. The device is capable of storing a bit of information; a control device for opening or closing gates; a toggle.


Two or more sets of information so arranged that an entry in one set selects one or more entries in the remaining sets; a dictionary; a device constructed of hardware, or a subroutine, which can either (a) decode multiple inputs into a single output or (b) encode a single input into multiple outputs; a tabulation of the values of a function for a set of values of the variable.


A circuit which has the ability to produce an output which is dependent upon a specified type of or the co-incidence nature of the input, e.g., an "and" gate has an output pulse when there is time coincidence at all inputs; an "or" gate has an output when any one or any combination of input pulses occur in time coincidence; any gate may contain a number of "inhibits," in which there is no output under any condition of input if there is time coincidence of an inhibit or "except" signal.


A circuit having two output points, S and C, and two input points, A and B, such that the output is related to the input according to the following table:

                      INPUT                  OUTPUT
                     A     B                 S    C
                     0     0                 0    0
                     0     1                 1    0
                     1     0                 1    0
                     1     1                 0    1

If A and B are arbitrary input pulses, and S and C are "sum without carry" and carry, respectively, it may be seen that two half-adders, properly connected may be used for performing binary addition.


The mechanical, magnetic, electronic, and electrical devices from which a computer is fabricated; the assembly of material forming a computer or component thereof.


An aggregation of data.


A set of characters which defines an operation together with one or more addresses (or no address) and which, as a unit, causes the computer to operate accordingly on the indicated quantities. The term "instruction" is preferable to the terms "command" and "order;" command is reserved for electronic signals; order is reserved for "the order of the characters" (implying sequence) or "the order of the interpolation," or "the order of the differential equation."


Expressions which define the operations of a computer, usually intelligible to the computer by means of it circuitry. It may be information recorded in a form which may be made available to a computer; coded information which can be sensed by a machine.


The science that deals with the cannons and criteria of validity in thought and demonstration; the science of the formal principles of reasoning; the basic principles and applications of truth tables, gating, interconnection, etc. required for arithmetic computation in a computer.


The term "storage" is preferred.


A millionth part of a second. Abbreviated musec.


A thousandth part of a second. Abbreviated msec.


A human blunder which results in an incorrect instruction in a program or in coding, an incorrect element of information, or an incorrect manual operation. See Error.


A numerical value written in the base-two system of notation. Usually the characters 0 and 1 are used to express numbers, although any pair of arbitrary symbols could be used.


A defined action; the action specified by a single computer instruction or pseudo-instruction; an arithmetical, logical, or transferal unit of a problem, usually executed under the direction of a subroutine.


An operation in which numerical quantities form the elements of the calculation (e.g., addition, subtraction, multiplication, division).


The processing of data in synchronism or in coincidence with a physical process in such a fashion that the results of the data-processing are useful to the physical operation.


The flow of information through a computer in time sequence, using only one digit, word, line or channel at a time. Contrasted with parallel operation.


A logical operator which has the property such that if P or Q are two statements, then the statement "P or Q" is true or false precisely according to the following table of possible combinations:

              P               Q            P or Q
          False  0        True   1        True   1
          True   1        False  0        True   1
          True   1        True   1        True   1
          False  0        False  0        False  0
The term disjunction is applied to this operator.


Information transferred from the internal storage of a computer to secondary or external storage; information transferred to any device exterior to the computer.


Handled simultaneously in separate facilities; operating on two or more parts of a word or item simultaneously; contrasted with serial.


A removable panel containing an ordered array of terminals which may be interconnected by short electrical leads according to a prescribed pattern and hence designating a specific program or machine step. The entire panel, pre- wired, may be inserted for different programs. Used to a large extent in CPC's, printers, tabulators, summary punches and some computers e.g., the Univac File Computer.


The degree of exactness with which a quantity is stated; a relative term often based on the number of significant digits in a measurement. See also Accuracy.


A person who prepares instruction sequences without necessarily converting them into the detailed codes of a particular computer. PUNCH, CARD A device which perforates or places holes in cards in specific locations designated by a program.


Access to storage under conditions in which the next position from which information is to be obtained is in no way dependent on the previous one.


To copy, usually from one form of storage to another, particularly from external or secondary storage to internal storage; to sense the meaning or arrangements of hardware; to sense the presence of information on a recording medium.


A mechanism that permits the sensing of information punched on cards by means of wire brushes, metal feelers, or a photoelectric device, converting the information into electrical pulses that are sensible to the computing system.


A device capable of restoring to a train or sequence of electrical pulses, information recorded on a magnetic tape in the form of a series of magnetized spots, usually for the purpose of transferring the information to some other storage medium.


A device capable of restoring to a train or sequence of electrical pulses, information punched on a paper tape in the form of a series of holes, usually for the purpose of transferring the information to some other storage medium.


The performance of a computation during the actual time that the related physical process transpires in order that results of the computations are useful in guiding the physical process.


A set of coded instructions arranged in proper sequence to direct the computer to perform a desired operation or series of operations.


One performance of a program on a computer; performance of one routine, or several routines automatically linked so that they form an operating unit, during which manual manipulations are not required of the computer operator.


An instrument which automatically samples or interrogates the state of various processes, conditions, or physical states and initiates action in accordance with the information obtained. SENSE To examine, particularly relative to a criterion; to determine the present arrangement of some element of hardware, especially a manually-set switch; to read holes punched in paper.


A machine which puts items of information into a particular order, e.g., it will determine whether A is greater than, equal to, or less than B, and sort or order accordingly.


Preferred to memory, any device into which units of information can be copied, which will hold this information, and from which the information can be obtained at a later time; devices, such as plugboards, which hold information in the form of arrangements of physical elements, hardware, or equipment; the erasable storage in any given computer.


Any storage system which utilizes the magnetic properties of materials to store information.


Columns of a liquid mercury medium used as a storage element by the delaying action or time of travel of sonic pulses which are circulated by having electrical amplifier, shaper, and timer circuits complete the loop.


Storage in which all bits, or characters, or (especially) words are essentially equally available in space, without time being one of the coordinates. Parallel storage contrasts with serial storage. When words are in parallel, the storage is said to be parallel by words; when characters within words (or binary digits within words or characters) are dealt with simultaneously, not one after the other, the storage is parallel by characters (or parallel by bit respectively). Contrasted with Storage, Parallel.


Storage in which time is one of the coordinates used to locate any given bit, character, or (especially) word. Storage in which words, within given groups of several words, appear one after the other in time sequence, and in which access time therefore includes a variable latency or waiting time of from zero to many-times, is said to be serial by word. Storage in which the individual bits comprising a word appear in time sequence is serial by bit. Storage for coded-decimal or other non-binary numbers in which the characters appear in time sequence is serial by character; e.g., magnetic drums are usually serial by word but may be serial by bit, or parallel by bit, or serial by character and parallel by bit etc.


The set of instructions necessary to direct the computer to carry out a well defined mathematical or logical operation; a subunit of a routine. A subroutine is often written in relative or symbolic coding even when the routine to which it belongs is not. SYSTEM An assembly of components united by some form of regulated interaction; an organized whole.


A machine which reads information from one medium, e.g., cards, paper tape, magnetic tape, etc. and produces lists, tables, and totals on separate forms or continuous paper.


A tape or ribbon of any material impregnated or coated with magnetic material on which information may be placed in the form of magnetically polarized spots.


An electronic device utilizing semi-conductor properties to control the flow of currents from one source in one circuit by currents from another circuit, e.g., a triod transistor permits the control of current in one circuit by the use of a smaller current in another circuit, with the transistor common to both circuits.


An electronic vacuum tube containing a screen on which information may be stored by means of a multigrid modulated beam of electrons from the thermionic emitter, storage effected by means of charged or uncharged spots; a storage tube; a Williams tube; an oscilloscope tube; a picture tube.


A set of characters which occupies one storage location and is treated by the computer circuits as a unit and transported as such. Ordinarily a word is treated by the control unit as an instruction, and by the arithmetic unit as a quantity. Word lengths are fixed or variable depending on the particular computer.

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