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	Glossary of Computer Software Development Terminology The terms are defined, as much as possible, using available standards. The source of such definitions appears immediately following the term or phrase in parenthesis, e.g. (NIST). The source documents are listed at the bottom of this page.
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	unambiguous. (1) Not having two or more possible meanings. (2) Not susceptible to different interpretations. (3) Not obscure, not vague. (4) Clear, definite, certain. underflow. (ISO) The state in which a calculator shows a zero indicator for the most significant part of a number while the least significant part of the number is dropped. For example, if the calculator output capacity is four digits, the number .0000432 will be shown as .0000. See: arithmetic underflow. underflow exception. (IEEE) An exception that occurs when the result of an arithmetic operation is too small a fraction to be represented by the storage location designated to receive it. unit. (IEEE) (1) A separately testable element specified in the design of a computer software element. (2) A logically separable part of a computer program. Syn: component, module. UNIX. A multitasking, multiple-user (time-sharing) operating system developed at Bell Labs to create a favorable environment for programming research and development. usability. (IEEE) The ease with which a user can learn to operate, prepare inputs for, and interpret outputs of a system or component. user. (ANSI) Any person, organization, or functional unit that uses the services of an information processing system. See: end user. user's guide. (ISO) Documentation that describes how to use a functional unit, and that may include description of the rights and responsibilities of the user, the owner, and the supplier of the unit. Syn: user manual, operator manual. utility program. (ISO) A computer program in general support of the processes of a computer; e.g., a diagnostic program, a trace program, a sort program. Syn: service program. See: utility software. utility software. (IEEE) Computer programs or routines designed to perform some general support function required by other application software, by the operating system, or by the system users. They perform general functions such as formatting electronic media, making copies of files, or deleting files.

	Source Documents The New IEEE Standard Dictionary of Electrical and Electronics Terms, IEEE Std. 100-1992. IEEE Standards Collection, Software Engineering, 1994 Edition, published by the Institute of Electrical and Electronic Engineers Inc. National Bureau of Standards [NBS] Special Publication 500-75 Validation, Verification, and Testing of Computer Software, 1981. Federal Information Processing Standards [FIPS] Publication 101, Guideline For Lifecycle Validation, Verification, and Testing of Computer Software, 1983. Federal Information Processing Standards [FIPS] Publication 105, Guideline for Software Documentation Management, 1984. American National Standard for Information Systems, Dictionary for Information Systems, American National Standards Institute, 1991. FDA Technical Report, Software Development Activities, July 1987. FDA Guide to Inspection of Computerized Systems in Drug Processing, 1983. FDA Guideline on General Principles of Process Validation, May 1987. Reviewer Guidance for Computer Controlled Medical Devices Undergoing 510(k) Review, Office of Device Evaluation, CDRH, FDA, August 1991. HHS Publication FDA 90-4236, Preproduction Quality Assurance Planning. MIL-STD-882C, Military Standard System Safety Program Requirements, 19JAN1993. International Electrotechnical Commission, International Standard 1025, Fault Tree Analysis. International Electrotechnical Commission, International Standard 812, Analysis Techniques for System Reliability - Procedure for Failure Mode and Effects Analysis [FMEA]. FDA recommendations, Application of the Medical Device GMP to Computerized Devices and Manufacturing Processes, May 1992. Pressman, R., Software Engineering, A Practitioner's Approach, Third Edition, McGraw-Hill, Inc., 1992. Myers, G., The Art of Software Testing, Wiley Interscience, 1979. Beizer, B., Software Testing Techniques, Second Edition, Van Nostrand Reinhold, 1990. Additional general references used in developing some definitions are: Bohl, M., Information Processing, Fourth Edition, Science Research Associates, Inc., 1984. Freedman, A., The Computer Glossary, Sixth Edition, American Management Association, 1993. McGraw-Hill Electronics Dictionary, Fifth Edition, 1994, McGraw-Hill Inc. McGraw-Hill Dictionary of Scientific & Technical Terms, Fifth Edition, 1994, McGraw-Hill Inc.. Webster's New Universal Unabridged Dictionary, Deluxe Second Edition, 1979. The bulk of this information was obtained from FDA.gov.

BIOS. basic input/output system.

bps. bits per second.

band. Range of frequencies used for transmitting a signal. A band can be identified by the difference between its lower and upper limits, i.e. bandwidth, as well as by its actual lower and upper limits; e.g., a 10 MHz band in the 100 to 110 MHz range.

bandwidth. The transmission capacity of a computer channel, communications line or bus. It is expressed in cycles per second [Hz], and also is often stated in bits or bytes per second. See: band.

bar code. (ISO) A code representing characters by sets of parallel bars of varying thickness and separation that are read optically by transverse scanning.

baseline. (NIST) A specification or product that has been formally reviewed and agreed upon, that serves as the basis for further development, and that can be changed only through formal change control procedures.

BASIC. An acronym for Beginners All-purpose Symbolic Instruction Code, a high-level programming language intended to facilitate learning to program in an interactive environment.

basic input/output system. Firmware that activates peripheral devices in a PC. Includes routines for the keyboard, screen, disk, parallel port and serial port, and for internal services such as time and date. It accepts requests from the device drivers in the operating system as well from application programs. It also contains autostart functions that test the system on startup and prepare the computer for operation. It loads the operating system and passes control to it.

batch. (IEEE) Pertaining to a system or mode of operation in which inputs are collected and processed all at one time, rather than being processed as they arrive, and a job, once started, proceeds to completion without additional input or user interaction. Contrast with conversational, interactive, on-line, real time.

batch processing. Execution of programs serially with no interactive processing. Contrast with real time processing.

baud. The signalling rate of a line. It's the switching speed, or number of transitions [voltage or frequency change] made per second. At low speeds bauds are equal to bits per seconds; e.g., 300 baud is equal to 300 bps. However, one baud can be made to represent more than one bit per second.

benchmark. A standard against which measurements or comparisons can be made.

bias. A measure of how closely the mean value in a series of replicate measurements approaches the true value. See: accuracy, precision, calibration.

binary. The base two number system. Permissible digits are "0" and "1".

bit. A contraction of the term binary digit. The bit is the basic unit of digital data. It may be in one of two states, logic 1 or logic 0. It may be thought of as a switch which is either on or off. Bits are usually combined into computer words of various sizes, such as the byte.

bits per second. A measure of the speed of data transfer in a communications system.

black-box testing. See: testing, functional.

block. (ISO) (1) A string of records, words, or characters that for technical or logical purposes are treated as a unity. (2) A collection of contiguous records that are recorded as a unit, and the units are separated by interblock gaps. (3) A group of bits or digits that are transmitted as a unit and that may be encoded for error-control purposes. (4) In programming languages, a subdivision of a program that serves to group related statements, delimit routines, specify storage allocation, delineate the applicability of labels, or segment parts of the program for other purposes. In FORTRAN, a block may be a sequence of statements; in COBOL, it may be a physical record.


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