Introduction

The Hall A base equipment for experiments consists of two general purpose, similar, superconducting spectrometers and their associated detector packages as well as several specific function systems (i.e. cryogenic targets, $\vec{\rm ^3He}$ target, beam current monitors, ARC energy measurement system, e-p energy measurement systems and so on). Each of these major systems is, typically, composed of several sub-system levels which need to be interlocked for protection of human life and/or equipment, monitored for operational status and commanded to perform various operations so that the system as a whole is able to perform the desired measurement or function. Most of these sub-systems have an infrastructure role; they are essential for the correct operation of the major system of which they are part but, in themselves, are irrelevant for the experimental physics data being acquired. An example could be the cryogenics of one of the spectrometer magnets; proper cryogenics filling of the magnets is absolutely essential for the magnets to operate but, for a given experiment, the relevant quantities are the spectrometer momentum and optics produced by the various active magnets and not the cryogenics levels of each magnet. The task of monitoring and commanding the infrastructure of the various Hall A systems falls on a distributed computer system loosely referred to as ``slow controls'' or ``Hall A Controls (HAC)''.