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Glossary
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Host Link System One or more host computers connected to one or more PCs through Host
Link Units so that the host computer can be used to transfer data to and re-
ceive data from the PC(s). Host Link Systems enable centralized manage-
ment and control of a PC System.
Host Link Unit An interface used to connect a PC to a host computer in a Host Link System.
host computer A computer that is used to transfer data or programs to or receive data or
programs from a PC in a Host Link System. The host computer is used for
data management and overall system control. Host computers are generally
small personal or business computers.
HR area A data area used to store and manipulate data and to preserve data when
power to the PC is turned OFF.
I/O capacity The number of inputs and outputs that a PC is able to handle. This number
ranges from around one-hundred for smaller PCs to two-thousand for the
largest ones.
I/O devices The devices to which terminals on I/O Units, Special I/O Units, etc., are con-
nected. I/O devices may be either part of the Control System, if they function
to help control other devices, or they may be part of the controlled system.
I/O Link Created in an Optical Remote I/O System to enable input/output of one or
two IR words directly between PCs. The words are input/output between the
PC controlling the Master and a PC connected to the Remote I/O System
through an I/O Link Unit or an I/O Link Rack.
I/O Link Unit A Unit used with certain PCs to create an I/O Link in an Optical Remote I/O
System.
I/O point The place at which an input signal enters the PC System or an output signal
leaves the PC System. In physical terms, an I/O point corresponds to termi-
nals or connector pins on a Unit; in terms of programming, an I/O point corre-
sponds to an I/O bit in the IR area.
I/O response time The time required for an output signal to be sent from the PC in response to
and input signal received from an external device.
I/O Unit The most basic type of Unit mounted to a backplane to create a Rack. I/O
Units include Input Units and Output Units, each of which is available in a
range of specifications. I/O Units do not include Special I/O Units, Link Units,
etc.
I/O word A word in the IR area that is allocated to a Unit in the PC System.
increment Increasing a numeric value by 1.
initialization error An error that occurs either in hardware or software before the PC System
has actually begun operation, i.e., during initialization.
initialize Part of the startup process whereby some memory areas are cleared, system
setup is checked, and default values are set.
input The signal coming from an external device into the PC. Input often is used
abstractly or collectively to refer to incoming signals.