Base
This is the main core of EPICS, comprising the build system and tools, common and OS-interface libraries, network protocol client and server libraries, static and run-time database access routines, the database processing code, and standard record, device and driver support.
Modules
A multitude of device and record support software has been written at various EPICS sites to interface to different kinds of hardware. These modules cannot all be managed and distributed centrally as part of Base but are managed as modules instead.
Extensions
Access to individual pages for most of the standard EPICS user interface packages, host tools and network protocol clients.
Distributions
EPICS distributions are collections of EPICS software configurations that have been proven to work together. It is much quicker to download and install a pre-configured distribution than it would be to download, build, install and configure components separately.