Modify Termcap Files

Each terminal vendor would create a special and unique command set that was built into the terminal. Special commands, or sequences of characters, were required to produce bold, dim or otherwise highlighted characters. At the time, most terminals were monochrome with set character size, so the available options were limited. Other special commands included backwards scrolling, smooth scrolling, double height characters (which meant that you had to duplicate the line to get the bottom of the characters to line up) and limited sound, usually either a buzz or a beep

The computer system, then needed to be told what the command set of the terminal was. Large amounts of the hard drive were taken up with these tables, which described to the computer the command set of the terminal. Once the TERMinal? CAPability? or TERMCAP table was built, the computer knew what character sequence to use for the special commands of the terminal.