1-14 COMPUTER TERMINOLOGY

Minor Cycle. In a storage device which provides serial access to storage positions, the time interval between the appearance of corre-sponding parts of succes~ive words.

Mistake. See Error.

Modified Binary Code. See Chaps. 11 and 20.

Modifier. A quantity, sometimes the cycle index, used to alter the address of an operand.

Modify. (1) To alter in an instruction the address of the operand.

(2) To alter a subroutine according to a defined parameter.

Multiple-Address Code. See Instruction Code.

Multiplier. A device which has two or more inputs and whose output is a representation of the product of the quantities represented by the input signals. (See Chap. lS.)

NRZ, Non-Return to Zero Recording. See Chap. 19, Sect. 2.

NRZI, Non-Return to Zero, Invert Recording. See Chap. 19, Sect. 2.

Number. (1) Formally, an abstract mathematical entity which is a generalization of a concept used to indicate quantity, direction, etc. In this sense a number is independent of the manner of its representation.

(2) Commonly, a representation of a number as defined above (e.g., the binary number "10110," the decimal number "3695," or a sequence of pulses). (3) A word composed wholly or partly of digits, and per-haps a sign, which does not necessarily represent the abstract entity mentioned in the first meaning. Note. Whenever there is a possibility of confusion between meaning (1) and meaning (2) or (3), it is usually possible to make an unambiguous statement by using "number" for meaning (1) and "numerical expression" for meaning (2) or (3). See also Positional Notation.

Number, Double-Length. A number having twice as many digits as are ordinarily used in a particular computer.

Number System. See Positional Notation.

Octal. See Positional Notation.

Octonary. See Positional Notation.

One-Address Code. See Instruction Code.

On-Line Operations. See Real- Time Operation.

Operation Code. (1) The list of operation parts occurring in an instruction code, together with the names of the corresponding opera-tions (e.g., "add," "unconditional transfer," and "add and clear"). (2) Synonym for operation part of an instruction.

Arithmetical operations, operations in which numerical quantities form the elements of the calculation (e.g., addition, subtraction, mul-tiplication, division).

COMPUTER TERMINOLOGY AND SYMBOLS 1.15 Complete operation, an operation which includes (a) obtaining all operands from storage, (b) performing the operation, (c) returning resulting operands to storage, and (d) obtaining the next instruction.

Computer operation, the electronic operation of hardware result-ing from an instruction.

Logical operations, operations in which logical (yes-or-no) quan-tities form the elements being operated on (e.g., comparison, extrac-tion). A usual requirement is that the value appearing in a given column of the result shall not depend on the values appearing in more than one given column of each of the arguments.

Red tape operations, operations which do not directly contribute to the result; i.e., arithmetical, logical, and transfer operations used in modifying the address section of other instructions, in counting cycles, and in rearranging data.

Transfer operations (storage operations), operations which move information from one storage location or one storage medium to another (e.g., read, record, copy, transmit, exchange). Transfer is sometimes taken to refer specifically to movement between different media; storage to movement within the same medium.

Although many operations fit the above definitions of two or more of the terms arithmetical, logical, transfer, and red tape, these terms are frequently used loosely to divide the operations of a given routine or of a given instruction code into four mutually distinct classes depending on the primary function intended for the given operation in the case at hand.

Operation Part. In an instruction, the part that usually specifies the kind of operation to be performed, but not the location of the oper-ands. See also Instruction Code.

Or Circuit. Synonym for or gate.

Order. (1) Synonym for instruction. (2) Synonym for command.

(3) Loosely, synonym for operation part. Note. The use of "order" in the computer field as a synonym for terms similar to those above is losing favor owing to the ambiguity between these meanings and the more common meanings in mathematics and business.

Or Gate. A gate whose output is energized when anyone ^.01' more of the inputs is in its prescribed state. Thus, this gate performs the function of the logical inclusive-or.

Overflow. (1) The condition which arises when the result of an arithmetic operation exceeds the capacity of the number representation in a digital computer. (2) The carry digit arising from this condition.

Parallel. Pertaining to simultaneous transmission of, storage of, or logical operations on the parts of a word, character, or other subdivision of a word, using separate facilities for the various parts.

1-16 COMPUTER TERMINOLOGY

Parallel Digital Computer. One in which the digits are handled in parallel. Mixed serial and parallel machines are frequently called serial or parallel according to the way arithmetic processes are performed.

An example of a parallel digital computer is one which handles decimal digits in parallel, although it might handle the bits which comprise a digit either serially or in parallel.

Parity Check. See Check, Forbidden Combination.

Partial Carry. See Carry.

Place. In positional notation, a position corresponding to a given power of the base. A digit located in any particular place is a coefficient of a corresponding power of the base.

Point. In positional notation, the location or symbol which separates the integral part of a numerical expression from its fractional part.

For example, it is called the binary point in binary notation and the decimal point in decimal notation. If the location of the point is assumed to remain fixed with respect to one end of the numerical ex-pressions, a fixed-point system is being used. If the location of the point does not remain fixed with respect to one end of the numerical expressions, but is regularly recalculated, then a floating-point system is being used. Note. A fixed-point system usually locates the point by some convention, while the floating-point system usually locates the point by expressing a power of the base.

Positional Notation. One of the schemes for representing numbers, characterized by the arrangement of digits in sequence, with the under-standing that successive digits are to be interpreted as coefficients of successive powers of an integer called the base or radix of the number system. In the binary number system the successive digits are inter-preted as coefficients of the successive powers of the base two just as in the decimal number system they relate to successive powers of the base ten. In the ordinary number systems each digit is a character which stands for zero or for a positive integer smaller than the base.

The names of the number systems with bases from 2 to 20 are: binary, ternary, quaternary, quinary, senary, septenary, octonary (also octal), novenary, decimal, unidecimal, duodecimal, terdenary, quaterdenary, quindenary, sexadecimal (also hexadecimal), septendecimal, octodenary, novendenary, and vicenary. The sexagenary number system has a base of 60. The commonly used alternative of saying "base 3," "base 4," etc., in place of ternary, quaternary, etc., has the advantage of uniformity and clarity. Note. In the most common form of positional notation the expression

COMPUTER TERMINOLOGY AND SYMBOLS 1-17 is an abbreviation for the sum

n

±

L:

i= -m

where the point separates the positive powers from the negative powers, the ai are integers (0 < ai < r - 1) called "digits," and r is an integer, greater than one, called the base. Note 1. The base of a number is usually indicated by a vertical line following the number with the base, r, as a subscript. The decimal number 12 in octal and binary codes is written 12ho = 1418 = 110012. Note 2. For some purposes special rules are followed. In one such usage, the value of the base r is not constant.

In this case, the digits are coefficients of successive products of a non-constant sequence of integers.

Precision. The quality of being exactly or sharply defined or stated.

A measure of the precision of a representation is the number of dis-tinguishable alternatives from which it was selected, which is sometimes indicated by the number of significant digits it contains. See also Accuracy.

Program. (1) A plan for the solution of a problem. (2) Loosely, a synonym for routine. (3) To prepare a program.

Automatic programming, any technique in which the computer is used to help plan as well as to help code a problem. See Coding.

Optimum programming, improper terminology for minimal latency

.•• I coding, i.e., for producing a minimal latency routine. See Routine.

Programmed Check. See Check, Programmed.

Pseudo-Code. An arbitrary code, independent of the hardware of a computer, which must be translated into computer code if it is to direct the computer.

Radix. See Positional Notation.

Random Access. 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.

Read. To acquire information, usually by observing some form of storage. Note. Usually a process which can be called reading can also be called writing, depending on the point of view of the observer.

Real-Time Operation, On-Line Operation, Simulation. Processing data in synchronism with a physical process in such a fashion that the results of data processing are useful to the physical operation.

Redundancy Check. See Check, Forbidden Combination.

Reflected Binary Code. See Chaps. 11 and 20.