File Protection; Program Protection; File Protection Ring - Control Data 1700 Reference Manual

File Protection
Program Protection
The back of a tape reel has a slot near the hub for a plastic file protection
ring (Figure 4). Writing on a tape is possible only when the reel contains a
file protection ring. Reading from the tape is possible with or without the
ring. Removal of the file protection ring after writing avoids loss of valu-
able records due to accidental rewriting.
Figure 4. File Protection Ring
The 1700 I/O system has a program protect feature which reserves pro-
tected equipment for use by protected programs. A 608 or 609 Tape Trans-
port is protected by setting the PROGRAM PROTECT switch on the 1732
controller chassis which corresponds to the setting of its Unit Select switch.
When its PROGRAM PROTECT switch is set, all instructions for that tape
transport (except the two status requests) are rejected if their Program
Protect bit is not set or the 1704 protect system is not enabled. To explain
in more detail:
1) A protected program may select any unit that is physically in the
system, loaded, under external control, and Not Busy.
2)
An unprotected program cannot select a tape unit whose switch is
in the protected position.
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