capability is the access key provided by the server.

The transition from halted to going will fail if any EG data stream is associated with a tape stream which is not in the dev_open state.
While in the going state the close file procedure is not permitted on any tape stream which is associated with a EG data stream.
In the test state all data streams are enabled and will receive data. Data flow is controlled and checked normally but the data is discarded without being written to any device. The transition from halted to test does not require the EG data streams to have any current association and is always permitted as long as the current state is halted.

This procedure is used to control the state of the Tape Server as a part of the data acquisition system.
The state may be :-
halted - That is no data should be received from the data processors and no data written to the output devices. If the state is changing to halted from going then any data already received from the data processors may be written to the output devices but the tape server should control the data flow from the data processors so as to halt further data.
going - The tape server enables receipt of data from the data processors and is prepared to write any data received to the output devices. It should check that all devices which are associated with input data streams are in the open state and thus in fact ready for writing. Any data stream for which there is an empty association list should not be enabled for receipt of data.
test - In this state all data streams are enabled and will receive data. Data flow is handled normally and all normal checking occurs but the data is then discarded without writting to tape. This is a very useful diagnostic option.