Glossary • 319
Modular I/O System
ETHERNET TCP/IP
H
Hardware
Electronic, electrical and mechanic components of a module/subassembly.
Header
A portion of the data packet, containing, among others, the address informa-
tion of the receiver.
Host computer / Subscriber
Originally used to describe a central mainframe computer accessed from
other systems. The services provided by the subscriber can be called up by
means of local and remote request. Today, this term is also used to refer to
simple computers which provide particular central Services (i.e. UNIX-
Subscribers on the Internet).
HTML
Abbreviation of hypertext markup language
HTML is the description language for documents on the World Wide Web. It
contains language elements for the design of hypertext documents.
HTTP
(Hyper Text Transfer Protocol) client server TCP/IP protocol which is used
on the Internet or Intranets for exchanging HTML documents. It normally
uses port 80.
Hub
A device which allows communication between several network users via
twisted pair cable.
Similar to a repeater, but with many outputs, a hub is used to form a star to-
pology.
Hypertext
Document format used by HTTP. Hypertext documents are text files which
allow links to other text documents via particularly highlighted keywords.
