Editing EPICS (section)

==Architecture==
EPICS uses [[client–server]] and [[publish–subscribe]] techniques to communicate between computers.&nbsp;Servers, the “[[input/output]] controllers” (IOCs), collect experiment and control data in real time, using the measurement instruments attached to them.&nbsp;This information is then provided to clients, using the high-bandwidth Channel Access (CA)<ref name="epics-r3.14-reference-manual">{{cite web|url=http://www.aps.anl.gov/epics/base/R3-14/12-docs/CAref.html#port|title=EPICS R3.14 Channel Access Reference Manual|website=www.aps.anl.gov}}</ref> or the recently added pvAccess<ref name="epics-pvAccessCPP-specification-wiki">{{cite web|url=https://github.com/epics-base/pvAccessCPP/wiki/protocol|title=pvAccess Protocol Specification|website=github.com}}</ref><ref name="epics-pvxs-pva-network-configuration">{{cite web|url=https://epics-base.github.io/pvxs/netconfig.html|title=PVA Network Configuration|website=epics-base.github.io}}</ref> networking protocols that are designed to suit [[Real-time computing|real-time]] applications such as scientific experiments.

IOCs hold and interact with a database of "records", which represent either devices or aspects of the devices to be controlled.&nbsp;IOCs can be hosted by stock-standard servers or PCs or by [[VMEbus|VME]], [[MicroTCA]], and other standard [[embedded system]] processors.&nbsp;For "hard real-time" applications the [[RTEMS]] or [[VxWorks]] operating systems are normally used, whereas "soft real-time"&nbsp;applications typically run on [[Linux]] or [[Microsoft Windows]].

Data held in the records are represented by unique identifiers known as Process Variables (PVs).&nbsp;These PVs are accessible over the network channels provided by the CA/pvAccess protocol.

Many record types are available for various types of input and output (e.g., analog or binary) and to provide functional behaviour such as calculations.&nbsp;It is also possible to create custom record types. Each record consists of a set of fields, which hold the record's static and dynamic data and specify behaviour when various functions are requested locally or remotely. Most record types are listed in the [https://wiki-ext.aps.anl.gov/epics/index.php/RRM_3-14 EPICS record reference manual].

[[Graphical user interface]] packages are available, allowing users to view and interact with PV data through typical display widgets such as dials and text boxes.&nbsp;Examples include EDM (Extensible Display Manager), MEDM ([[Motif (software)|Motif]]/EDM), and [https://controlssoftware.sns.ornl.gov/css_phoebus CSS].

Any software that implements the CA/pvAccess protocol can read and write PV values.&nbsp;Extension packages are available to provide support for [[MATLAB]], [[LabVIEW]], [[Perl]], [[Python (programming language)|Python]], [[Tcl]], [[ActiveX#ActiveX|ActiveX]], etc. These can be used to write scripts to interact with EPICS-controlled equipment.