Expansion units 7104 is an optional feature that you can order for your model 9406-270. The 7104 is physically attached to the right side of the base system tower.

Model 9406-270 can use the optional external IBM® uninterruptible power supply that acts like a BBU (Backup Battery Unit). The uninterruptible power supply has power cords that connect the uninterruptible power supply to the base system, the 7104 expansion unit, and a power cord that connects the uninterruptible power supply to the power outlet.