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Appendix A: Glossary
A-2
AIX. The IBM variation of UNIX that runs on IBM computers.
Anonymous FTP. A method by which any user on a network can access certain files on a given
host computer by logging in under the name anonymous after connecting to that computer with
the FTP protocol.
AppleTalk. A protocol developed by Apple Computer for file sharing and print sharing.
AppleTalk runs over Ethernet, LocalTalk, and Token Ring.
ARP Address Resolution Protocol is a protocol for mapping an IP address to a physical ma-
chine address (the physical machine address is also known as a Media Access Control or MAC
address.) that is recognized in the local network. For example, in IP Version 4, the most common
level of IP in use today, an address is 32 bits long. In an Ethernet local area network, however,
addresses for attached devices are 48 bits long. A table, usually called the ARP cache, is used to
maintain a correlation between each MAC address and its corresponding IP address. ARP pro-
vides the protocol rules for making this correlation and providing address conversion in both di-
rections.
ASCII. American National Standard Code for Information Interchange. ASCII represents the
western character sets based on the ANSI X3.XX standard. There are many variants of this
standard, typically to allow different code pages for language encoding, but they all basically fol-
low the same format. ASCII is essentially a 7-bit code which allows the 8th most significant bit
(MSB) to be used for error checking, however most modern computer systems tend to use
ASCII values of 128 and above for extended character sets.
AT&T UNIX. One of two major variants of UNIX on which operating systems like HP/UX,
Solaris, and SCO UNIX are based. Originally developed by AT&T.
AUI. Attachment Unit Interface; the 15-pin Ethernet connector that is used to connect to a
transceiver. Also called a DIX connector or a thick Ethernet port. See also 10base5.
Batch File. A file containing a number of system-level commands. When this file is run, each of
the commands in the file are executed, thereby eliminating the need to type in each command indi-
vidually.
Berkeley UNIX. One of two major variants of UNIX on which operating systems like Digital
UNIX and SunOS are based. Originally developed by the University of California-Berkeley.
Bidirectional. Capable of communications in two directions. With printers, this usually means
that the printer is capable of receiving data and sending back status information to the host com-
puter.