Page:CTSS programmer's guide.djvu/45

 his files, or else older files will be dumped automatically for him at disk editor time. If at shut-down time the user himself has already exceeded his quota, no further extension will be allowed; his machine status will be lost and so may his message.

Assignment of Input-Output Units
There are numerous devices such as tape units, scopes, plotters, satellite computers, etc., which are of such a nature that it is desirable to assign them to a single user for his session at his console. This assignment is done by means of an  command, where the user may receive a busy signal whenever requested units are actively engaged. Addressing conventions of input-output units will always be by logical unit numbers except when location is relevant.

The supervisor will maintain for each user an input-output assignment table in which the logical-physical unit number interconnection will be kept. When a user gives a  command at his console at the end of his session, all assigned units will be disconnected.

Magnetic Tape Usage
Although for a large number of cases the disk memory, because of its quasi-random access, is more appropriate for program data and temporary storage requirements, there are still many problems such as payrolls, bubble chamber scanner output, etc., where magnetic tapes are more appropriate. This is true partly because of the vast quantities of information.

Within CTSS, the user may use private tape reels in the following way. The user types in an  command specifying, for example, that file-protected private tape reel 103 should be mounted as logical tape 2 on logical channel 2. The computer replies "WAIT," as the command requests from the supervisor pool an available tape drive. Upon receipt of an appropriate tape drive assignment, the  command sends an interconsole message to the tape operator's console (where his program is continuously processing messages), of the form:

"mount reel 103 as tape A3, file protected."

The tape operator, on completing the action, types "ok" which causes 31