we show a display control unit (DCU) in figure 8-30. Remote units are also available to provide initial startupjust like the operator and display control units. Control,data entry, and data display man/machine interfaces ofmainframes are your primary means of operating andmaintaining a mainframe computer. You can control alloperations from this man/machine interface. Newermainframes, in addition to controls, switches, andpushbutton indicators, use displays and keyboards todisplay status and to address the contents of registers. EXECUTE INTERNAL DIAGNOSTICS. Onmainframes, internal diagnostics are also availableusing built-in tests (BITs) or tests available on anNDRO. They are designed to test the computerhardware (CPU, IOCs, and any optional circuits) andreturn pass/fail results to the operator. Pass/fail resultsare displayed on the control, data entry, and data displayman/machine interface shown on figure 8-30. Similarto minicomputers, the BIT itself can consist of severallevels of tests and subtests controlled from thecomputers front panel. Some internal diagnostics aredesigned to test all or selected sections of the computer. Errors can be displayed on the front panel using the datadisplay man/machine interface. The computerstechnical manuals will enable you to decipher the errorFigure 8-30.Example of a display control unit.