Upgrade Units can be used for player's convenience and help with current tasks at hand:

Near the northmost entrance to the Escape Pods (at the bottom of the ladder) is a Tech Upgrade Unit.

Far to the south of the Escape Pods lies a Weapons Upgrade Unit.

From the main Elevator: through the door to the south and around the bend is a dead-end with a broken Replicator and Stats and Psi Upgrade Units.

In the Security room past the Theater and Casino, Weapons and Psi Upgrade Units can be found.

The Mall's first floor has two Stats and two Tech Upgrade Units (for some reason they're doubled) close to the nearby O/S Upgrade Machine.

All four types of Upgrade Units will be on a wall opposite a desk.

From the Elevator or Med Annex, head towards Athletics.

Upgrade Units of all four varieties are in a small chamber with a corpse in it.

In Sector D (through Bulkhead 43), head west before Fluid Ops and proceed down the hall past the Barracks.

The Lounge in Sector C (through Bulkhead 42) also has all four types of Upgrade Units, two on lower, two on higher floor.

All four types of Upgrade Units can be found on the second floor of the Lounge outside the Crew Quarters.

In Sector A, right outside the bulkhead, Stats and Weapons Upgrade Units can be found.

Psi and Tech Upgrade Units can be found through the door to the east of the Von Braun's central Elevator.Stats and Tech Upgrade Units can be found in Command Control.Weapons and Psi Upgrade Units can be found in the Security Room near the entrance to the Cargo Bays.Just through the door to the Crew Annex, all four types of Upgrade Units are found in a lounge area, near a bulkhead leading back to the Science section.

After exiting Cryo-Recovery A, all four types of Upgrade Units can be found on the faces of the center column in the next room.

System shock 2 research descriptions