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2 Control Switch
3 Control Switch
4 Control Switch
The Communicator must be installed in all tape controls to be switched. Using a
combination of the Communicator and the 2, 3, or 4 Control Switch special
features, two, three, or four interconnected tape controls can address a maximum
of 16 tape units. Figure 5 shows some possible switching configurations.
The 2 Control Switch is a 2 x 8 configuration of hardware switching logic. Tape
Units 0-7 (attached to Tape Control 1 in part 1 of Figure 5) can be accessed by
the Communicator in Tape Control 2 as well as the Communicator in Tape
Control 1. A 2 x 16 configuration is obtained by installing a 2 Control Switch in
Tape Controls 1 and 2, allowing the Communicators in each tape control to
access its own eight 3420s as well as the 3420s of the other tape controL (See
part 2 of Figure 5).
A 3 x 16 configuration is obtained by installing a 3 Control Switch in Tape
Controls 1 and 2. A third tape control must be added to the configuration. Tape
Control 3 does not contain any switch hardware or attach any tape units, but
does contain a Communicator (see part 2 of Figure 5).
A 4 x 16 configuration is obtained by installing a 4 Control Switch in Tape
Controls 1 and 2. Two more tape controls must be added to the configuratjon.
Tape Controls 3 and 4 do not contain any switch hardware or attach any tape
units, but each contains a Communicator (see part 2 of Figure 5).
The 3 Control Switch and the 4 Control Switch are expansions of the 2 Control
Switch. They allow access to the eight attached tape units by the additional
Communicators.
In all of the configurations, the device switch is logically invisible except for a
'busy' response to initial selection when the addressed tape unit is being used by
another tape control. All device switch features contain priority logic to;
systematically allocate a tape unit in the event of conflicting tape control
requests.
Section 1: Introduction
1 7
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