What is the basic difference between Unit and Devices?

What is the basic difference between Unit and Devices?

Devices are components / equipment/ products or services which together enter into a functional relationship and enable the final product / UNIT to be formed.

UNIT is a collection of devices working in a synchronised way to achieve a designated level of performance.

Unit could become a device for another larger unit and often devices include smaller basic components that enable a device to be readied