we show a display control unit (DCU) in figure 8-30.
Remote units are also available to provide initial startup
just like the operator and display control units. Control,
data entry, and data display man/machine interfaces of
mainframes are your primary means of operating and
maintaining a mainframe computer. You can control all
operations from this man/machine interface. Newer
mainframes, in addition to controls, switches, and
pushbutton indicators, use displays and keyboards to
display status and to address the contents of registers.
EXECUTE INTERNAL DIAGNOSTICS.— On
mainframes, internal diagnostics are also available
using built-in tests (BITs) or tests available on an
NDRO. They are designed to test the computer
hardware (CPU, IOCs, and any optional circuits) and
return pass/fail results to the operator. Pass/fail results
are displayed on the control, data entry, and data display
man/machine interface shown on figure 8-30. Similar
to minicomputers, the BIT itself can consist of several
levels of tests and subtests controlled from the
computer’s front panel. Some internal diagnostics are
designed to test all or selected sections of the computer.
Errors can be displayed on the front panel using the data
display man/machine interface. The computer’s
technical manuals will enable you to decipher the error
Figure 8-30.—Example of a display control unit.
8-24
