operation and maintenance of a microcomputer can be accomplished. Keyboards come in many shapes and sizes, have different numbers and arrangements of keys, differ in respect to touch, and have special keys to allow you to communicate  specific  software  commands.  Most manufacturers  have  designed  their  keyboards  as separate devices so you can place them wherever it is convenient  (even  in  your  lap).  Other  manufacturers have designed their keyboards into the display/monitor device or system unit. Refer to figure 3-9 for an illustration of a typical keyboard used with a PC. The important things you need to know about keyboards are the types of keys and the function and the placement  of  each  key.  All  keyboards  have  the alphabetic characters (upper and lower case), numbers, and  some  special  characters.  In  addition,  keyboards have special function keys and control keys that are defined by the operating. system or the program. It is important to remember that any key or combination of keys can be assigned special meaning by a program. Therefore, the keys may have different meanings and functions  depending  on  the  program  you  are  using. Once  again,  we  remind  you,  read  all  the  documentation that comes with each program and with the computer system. The keyboard has the following three levels of controls and indications: Initiate computer operations Control  computer  operations Testing In addition to a keyboard, a microcomputer may have a mouse. The  mouse can be used with the monitor as  a  controlling  device  after  the  computer  has  been booted and the operating program has been initialized. The operational program must be specially designed to interface with a mouse. TELETYPES Teletypes can be used as input/output communica- tions  consoles  (IOCCs).  They  are  used  primarily  as means of inputting information to the computer and receiving information from the computer. Teletypes have  a  keyboard  for  inputting  and  a  printer  for outputting. Once you have loaded the programs/ software   (operational   or   maintenance)   into   the computer, an IOCC or terminal of control (TOC) is used to initialize the programs and communicate with the computer   when   operating   during   operations   or maintenance. You  use  the  keyboard  to  give  the computer commands and parameters and the printer portion to repeat back commands and parameters and provide  status  of  equipment  or  software  and  test completions. The commands used to communicate with the computer are specific to the operating system and the operational  or  maintenance  programs.  You  can  find  the Figure 3-9.—Example of a typical keyboard used with a PC. 3-12