Client identifier identifies the device for the client and capability is the corresponding access key provided by the server for the device.
volume name specifies the name of the volume be to loaded onto the allocated device.
The current stream state for the stream must be dev_alloc otherwise the request will fail.

If procedure status = accepted the current value of the stream status for this stream changes to dev_mounting.

When the mount operation has been completed successfully (which could take some time) then stream state for the stream changes to dev_mount.

Should the mount operation fail (for example the requested volume cannot be found) then stream state reverts to dev_alloc and procedure status is set appropriately.

See also procedure 14 - identify volume.

Two procedures are provided (Mount Volume and Identify Volume) which supply the volume name to the server which is used when writing file labels. For tape devices either can be used. For the special devices FILE and SINK however only the Mount Volume procedure should be used. For the device SINK it is permitted that a null string be supplied as the volume name.
The server records the volume name supplied in the control table for the drive. In most cases no further action is required and the drive state changes to the mounted state. It is assumed that the user has inserted the correct tape cassette into the drive (this is checked later during the Open procedure). However for magnetic tape devices allocated as a result of the client supplying a generic name in the Allocate procedure the server will request confirmation that the correct tape cassette has been loaded into the required drive and the drive state will be mounting until this confirmation is received. This option is intended for remote operation of the system and assumes that system operators are available to load the requested tape cassette rather in the manner of batch mainframe computer systems. Currently the Eurogam control software does not use this option.