checksum: Simple error detection method. A value derived by using the output of a mathematical computation performed on a block of data to determine if any of the data has been corrupted. Normally found in the header of a data message.

chfn: Change finger. Command used to change the data in the /etc/passwd file that is read by the finger command.

dmesg: Display messages. Command used to turn on and off the writing of messages to the console.

Ethernet: Local area network developed by Xerox, Intel and DEC in 2973. Ethernet is a passive system connected by either thicker shielded coaxial cable of thinner non-shielded coaxial cable or thinner non-shielded cable with a 10 megabits-per-second standard.

flicker: Disruptive flashing light coming from a monitor, resulting in eye fatigue. Caused by a refresh rate that is too slow for the brightness of the screen.

interlacing: Process of scanning video images on a screen by alternating between odd and even lines, allowing low-resolution monitors to display at higher resolution. Normally, use of interlacing results in flicker.

ISDN: Integrated services digital network is a set of specifications for end-to-end integrated voice, video, digital data and packet switch data network. There are two ISDN configurations: basic rate interface (BRI), which provides two B-channels and one D-channel; and primary rate interface (PRI), which offers 23 B-channels and one D-channel.

network layer: The network layer is responsible for routing, or determining the links necessary to get data from the sending to the receiving host. It is the third layer of the Open Systems Interconnection model or the second layer of the Transmission Control Protocol and Internet Protocol.

router: Intelligent bridge between networks and computers that is limited to passing data packets between systems running the same protocol. Operates at the network layer (layer3) of the Open Systems Interconnection model.

routing table: Table maintained on a router that is used to determine what the router is to do with incoming and outgoing packets of information.

shmop: Shared memory operations. System call used to set up and manage interprocess communications to manage shared memory.

swplo: Swap low. Kernel parameter used to specify the starting block number for the swap partition when the root partition and swap partition are mounted on the same disk device. Swap functions are now managed by swapctl.

UIMS: User interface management system. Also called graphical user interface builder. A set of tools used to help developers more easily create and test interfaces between the X Window System and an application being developed.

Copyright 1994 William H. Holt. Reprinted with permission from Unix: An Open Systems Dictionary, by William H. Holt & Rockie J. Morgan, published by Resolution Business Press.