Most CDs have two to four antennas fixiated to their head which are directly connected to their auditory entrance (or well, 'ears' as we would call it in human terms) which makes their antennas vital for their work and general hearing. Damaged or removed antennas may result in a CD losing their ability to hear or at least reduce it greatly.

Depending on the size of the antennas it's easy to see what purpose the CD served - long antennas are usually paired with long-range signals which put the individuals at use to distribute orders, arrange communication between ships & pods on their way to other exoplanets (when humans were still around) and to manage incoming signals from other planets & stations/outposts.

Short antennas usually indicated a more localized position for the drone in question - mainly within a singular Outpost or in ships to work directly connected to the local machinery and computers, sending orders in smaller ranged areas and storing security data.

Most CDs have secondary enhancers which work similar to a short-range antenna allowing them to switch between long and short range at will (mainly used for CDs that had flexible working places between ground & flight).

Generally, the antennas also function as "mood indicator". They can rotate around themselves and change position dependant on a fixed motion range around the head - similar to how e.g animals use their ears to indicate mood, CDs quickly took these habits from dogs that were around Copper-9 and video material of animals and copied them. Not all CDs did or do that, but alot of them do. For example if an individual is excited/attentive, the antennas would stick right up. If they're overwhelmed/annoyed/angry they'd usually be lowered down or pressed against the sides of the head.

They were expected to be very attentive and pay close attention to details. Their inner storage was designed to hold literal months and even years of auditory data that they recieved which was usually extracted every 4-6 months via the ports on their back which connected directly to the storage. Without these "clear outs" most CDs experience involuntary deletion of audio files which is out of their control and might result in them forgetting things they've heard/analyzed before.

Other than those two features their anatomy is fairly similar to that of normal Workers, height etc. as well.

After the humans disappearance alot of CDs lost their use as there... well, were no orders to share and no signals to analyze. Some of them struggled with this loss of "useability", some were fairly happy about this.

Lost/destroyed antennas cannot be restored by themselves (well, unless a CD is a Solver User like Kira) and CDs usually do not take well to losing or damaging antennas. Enhancers aren't as sensitive, but still hurt. Touching them might also cause disruption in hearing for CDs, it would be like someone rang a bell next to a humans ear for them. :'D (no touchie!)

CDs are generally connected to ECHO in the MD: Echo story (outside of that this plot point doesn't matter, just mentioning it here haha). Since Kira was the first CD Echo tried to use as host it developed an interested in them since CDs are great tools to be used for mass-ordering hosts.

Alot of CDs were destroyed while the humans were still around, especially if their warranty expired or they became damaged, to prevent sensitive information (such as orders and analyzed data) from leaking or being stolen by enemy forces/entities.