Command and Data Subsystem. The "Master Computer" of the
spacecraft. The CDS provides the interface between the ground and the spacecraft.
All commands are either directed to the CDS, passed by the CDS to other
subsystems (eg AACS), or control relays directly. The CDS also collects
data from all the subsystems and science instruments and formats them for
transmission to the ground.
The CDS has two strings also. In addition, complete copies of the
flight software are in the normal and extended (spare) memory on each string,
to enable rapid switching in case of a memory failure on one string.
More information on the CDS.