the DCU have surrounding barriers and interlocks to prevent  accidental  key  action.  The  DCU  display visually helps you to make the correct entries. The dot matrix display has six 44-character lines of status and maintenance data. You can monitor operations using the ac plasma display and the indicators. Interfacing (inspect and change and manual operations) with the CPU/IOC and memory is accomplished using the key switches.  Monitoring  capabilities  include  switch settings,  hardware  availability,  halts,  jump  stops, breakpoints, and operator input. Remember that key settings can interact with computer software. This DCU is located in the front of the frame/ cabinet. The DCU has a built-in microprocessor with five levels of controls and indications. They are as follows: Loading and initiating operations Monitoring  operations Status  indications Operator interfacing Testing (self) COMPUTER CONTROL PANELS Computer control panels are used to power up the CPU and for manual START, HALT, CLEAR, register display, and bootstrapping. The controls can initiate and monitor computer operations and load diagnostics contained  on  magnetic  tape  from  an  external  peripheral unit. Then, from a data terminal, you can perform diagnostics  on  the  computer.  Monitoring  capabilities include   switch   settings   and   display   registers. Remember that key settings can interact with computer software. Some computer control panels limit their access to authorized personnel only. A locked security cover must be removed to gain access to the panel’s switches. Figure 3-7 is an illustration of a computer control panel. This computer control panel has three levels of controls and indications. They areas follows: CPU  power Initiate   computer   operations   (includes maintenance) Monitor computer operations MAINTENANCE  CONSOLES Computer logic test sets (maintenance consoles) allow you to operate the computer set under expanded, and varied conditions, and at various speeds and various operating modes. The maintenance console’s primary purpose is to enable you to monitor instruction words and  input/output  commands  and  their  execution,  and  to view  the  contents  of  various  arithmetic  and  control registers. Monitoring capabilities include switch settings,  hardware  availability,  halts,  jump  stops, breakpoints, and operator input. Remember that switch settings can interact with computer software. The maintenance  console  can  be  divided  into  three  physical areas. They are as follows: Maintenance console control and indicator status CPU  portion IOC  portion Refer  to  figure  3-8  for  an  illustration.  This maintenance console may be located up to 15 feet from the computer set; but it is not designed to be mounted permanently   atop   the   computer’s   cabinet.   The maintenance  console  receives  its  power  from  the operator  panel  when  online.  When  the  maintenance Figure  3-7.—Example  of  a  computer  control  panel. 3-10