Requests a list of the device names available which may be specified in the allocate device procedure.

There are no procedure specific parameters.

This procedure returns a list of the data storage devices available to the server. Since this is a read-only procedure it is available to any client and no access key is needed. The actual information returned is system dependant. Each entry consists of a device status, a real device name and a generic device name.
For the Eurogam server the generic device name MTH is used for magnetic tape drives (Exabytes) and there are a number of real devices using the names MTH0, MTH1 etc. In addition to the magnetic tape devices for which there is one entry in the device list for each real device there are two special entries (SINK and FILE) which have these names as both the generic and real names. These special entries in fact imply a number of available devices limited by server implementation. FILE is a device in which the data is stored in the filestore and SINK is a device similar to /dev/null which can emulate the performance of any real tape drive by using a controlled time delay before discarding the data block.
Where the tape server has available tape drives of different capability (for example Exabyte, DAT and DLT) then each drive type can be assigned a different generic device name while using simple names of the form MTHx (where x is 0 => 9 and A => Z) to physical identify the real drives.
For each entry the status indicates if the real device is free (that is currently not in use) or allocated (see Claim procedure) and in use by this server.The Eurogam tape server is implemented within a multi-user real-time system which allows interactive user sessions to claim tape drives and so those available for use by the tape server may change with time. It also permits multiple copies of the tape server program to be run (connected to different experiments) which share a pool of tape drives and this also causes the list of free devices to change as drives are allocated to another server. Finally a system command interface allows the drive resource table to be dynamically modified. This is useful if a drive develops a fault and becomes unavailable for further use.