Glossary A - O

Glossary

A-O

ASCII (American Standard Code for Information Interchange)

A popular character set using one of 256 byte values to represent printable and non-printable characters. For example, a value of 65 represents an uppercase "A," and a value of 122 represents a lowercase "z." The ASCII character set includes upper-and lower-case English letters, the digits 0 through 9, common punctuation symbols, and a variety of non-printable control characters.

BACKUP SAVESET

A file produced by the OpenVMS BACKUP utility containing the data and metadata for one or more files. Used to archive backup copies of files, directory trees, or entire disk devices to be used in the event of data loss or hardware failure.

BOOT or BOOTSTRAP

The process of loading and starting an operating system. If the system has just been powered on, this is referred to as a "cold boot." If the system had previously been running an operating system, it is a "warm boot" or "reboot." In OpenVMS terminology, "reboot" is not synonymous with "restart." "Restart" refers to resuming an interrupted operating system already in memory.

BROADCAST MESSAGE

A message sent to one or more terminals. It may be sent by OpenVMS or by an appropriately privileged user.

CHARACTER

One element in an array (string) of text or other information. In the context of OpenVMS, the term usually refers to a member of the ASCII character set. A character is a single letter, digit, punctuation mark, or control character.

See also ASCII (American Standard Code for Information Interchange).

CLI (Command Line Interpreter or Interface)

That part of computer software that accepts user commands, either typed at a keyboard or read from a file, and causes them to be carried out. The default CLI under OpenVMS is the Digital command language (DCL).

COMPILED PROGRAM

A program produced by a language compiler from one or more language source files. OpenVMS compilers produce object files, which are then linked, creating executable programs.

CONSOLE SUBSYSTEM

Software that, among other things, assists with loading or bootstrapping an operating system, diagnostic functions, and updating CPU microcode. It may run on a dedicated processor, or on the main CPU of the system. It usually has control of the hardware when an operating system is not running.

See also SRM.

CONSOLE TERMINAL

A special terminal that receives system messages and security alarms, whose device name is OPA0:. For security reasons it is often located in a physically secure location.

CPU (Central Processing Unit)

A component in a computer that executes operating system and program instructions. A given computer system may have more than one CPU.

DCL (Digital Command Language)

The default command line interpreter of OpenVMS.

ENVIRONMENT VARIABLE

A setting stored in the nonvolatile memory of the computer, used to customize the actions of the console subsystem. Used to store such settings as the default boot device and what action to take when the computer is powered on.

EXTENT

One portion of a file stored on disk—also known as a fragment. A given file may be stored as one or more discontiguous extents.

FILE FRAGMENTATION

The occurrence of files being broken apart and stored at discontiguous locations on a disk. This is a normal by-product of file system activity. Utility programs exist to gather file fragments back together periodically to aid performance.

FILE HEADER

A 512-byte block in the reserved file INDEXF.SYS used to describe another file on the disk. Nearly all file attributes (name, owner, protection, size, etc.) are stored in the header.

HIBERNATE

The act of a process voluntarily entering a wait state until explicitly awakened by another process or by a scheduled wake-up request—also the name of the associated process-scheduling state.

LEXICAL FUNCTIONS

A set of function provided by the Digital command language providing a variety of services, including returning information about files and converting time formats.

MIPS (Millions of Instructions Per Second)

One measure of CPU performance. Used alone, it is not necessarily a reliable way to compare CPUs of different architectures.

ODS-2 (On-Disk Structure Version 2)

The primary on-disk file system layout used by OpenVMS.

ODS-5 (On-Disk Structure Version 5)

A newer file system layout providing for better compatibility with other file systems, such as those used with UNIX or Windows.