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 of printing, punched cards, or pen plotting, by the user's issuing appropriate delayed output commands. The output files must be stored by the user on the disk in appropriate formats. The delayed output commands initially will cause appropriate disk editor control cards to be generated by the supervisor and automatically inserted in the disk editing procedure; thus the delayed output occurs at disk editing time. The user can also by appropriate commands or supervisor calls generate other disk editor control cards to be entered into the disk editing process.

Disk Editing Control Cards
Periodically, requests will be processed by the Center Staff for input to the disk from cards and for output from the disk, either printed or punched. Control cards are submitted to the Center Dispatching Area which specify these requests. A variety of operations, specified by control cards, may be performed at disk-editing time, including, in addition to off-line input and output: editing of a binary program onto the disk; deletion of a file, with or without punched-card dumping; changing the mode of files (in particular of "read-only class 2" files); copying a user's file for another user; and linking several users (i.e., giving them access) to a particular user's file.

Disk Reliability, Malfunctions and Recovery
The 1301 disk memory is expected to be quite reliable - more so, for example, than tape - but to date enough information has not been gathered to offer any definite appraisal of its reliability.

During times when CTSS is not in operation, the disk may on occasion be used by other systems. For this reason, as well as to protect information from loss due to malfunction of the disk, the contents of the disk are dumped onto magnetic tapes as needed and at least once a day. These tapes are used to reload the disk at the same time that any requests for new input to the disk are being processed. Disk dump tapes are written in duplicate to safeguard against tape errors. Dump tapes will be kept for backup purposes for several days, and a set of dump tapes will also be preserved from certain fixed points 26