An EPICS Dictionary

Many technical terms are used in the EPICS community. For most of them the meaning is not clear for non-specialists. The following table will explain some of the terms.

Channel	This is only another term for Process Variable.

Channel Access	Channel Access is the communication protocol used by EPICS to transfer information through the network.

Channel Access Server	Software which implements Process Variables for the use with Channel Access. Simplified: Software which implements records. An IOC is also a Channel Access Server.

Channel Access Client	Software which allows access to Process Variables using Channel Access. For example `medm` is a Channel Access Client.

EPICS	Stands for Experimental Physics and Industrial Control System.

Input	Inside an EPICS environment, input means that information comes from the hardware to the user (or more technicaly: from the Channel Access Server to the Channel Access Client).

Input Output Controller (IOC)	An IOC is a computer running iocCore, a software package from the EPICS base release. It defines records to implement Process Variables. An IOC is as well an Channel Access Server as a Channel Access Client. This implies that IOCs can communicate with each other.

Output	Inside an EPICS environment, output means that information goes from the user to the hardware (or more technicaly: from the Channel Access Client to the Channel Access Server).

Process Variable (PV)	A PV is a piece of data which can be accessed by its unique name. Often the PV name consists of a record name and the name of a record field, connected by a dot. For example `AIRDI-PCT:CURRENT.EGU`. A PV is the basic data set of the Channel Access protocol.

Table:

Record	A Record is a collection of Process Variables which is implemented on an IOC. Dozens of Record Types exist, each with its own set of fields and functionality. The most common types are included in the EPICS base distribution. Be aware, that sometimes the terms Record, Channel and Process Variable are used synonymously. This is not correct!

Soft IOC	A computer (most often a PC) which is running iocCore not exclusively. Often, there is no hardware attached to the computer. At the SLS, VME computers are called IOC and PCs are called SoftIOC if they run EPICS.

VME	VME is not an EPICS term. It stands for VERSA Module Eurocard, which is a computer architecture. Unlike a PC, all cards are on a common bus.

If you find a term which is not mentioned here and which should be, please send me a mail to elke.zimochpsi.ch