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The first video terminals were nothing more than "glass teletypes".  That is, they simply replaced the paper with a video screen.  They often had the same restrictions as teletypes including uppercase only display.  However, free of mechanical constraints, they could operate at higher speeds than teletypes.  Obviously, there was no paper record of the output and so these devices were not appropriate for all applications.  Video terminals typically provided a 24 line by 80 column screen.  Each column position on each line is called a '''character cell''', which meant that each character took the same space on the screen, as opposed to proportional spacing. In place of a print head, a cursor was provided to indicate the location where the next output would show.  Cursors typically were inverse blocks or underscores, blinking or solid.  Each character was represented by a dot matrix (called a raster font) similar to dot-matrix print heads.

The first video terminals were nothing more than "glass teletypes".  That is, they simply replaced the paper with a video screen.  They often had the same restrictions as teletypes including uppercase only display.  However, free of mechanical constraints, they could operate at higher speeds than teletypes.  Obviously, there was no paper record of the output and so these devices were not appropriate for all applications.  Video terminals typically provided a 24 line by 80 column screen.  Each column position on each line is called a '''character cell''', which meant that each character took the same space on the screen, as opposed to proportional spacing. In place of a print head, a cursor was provided to indicate the location where the next output would show.  Cursors typically were inverse blocks or underscores, blinking or solid.  Each character was represented by a dot matrix (called a raster font) similar to dot-matrix print heads.

Second generation video terminals provided the ability to position the cursor at arbitrary locations on the screen, to change the characteristics of individual characters, such as blinking, bold, underlined, etc.  With each successive generation of video terminal, more features were added, including a choice of fonts, graphics symbols, changing screen resolution, and colors.  These features were selected by the output of special sequences of characters to the terminal.  The most common mechanism was to start the sequence with the ASCII escape code (ASCII value 27), hence they were called "escape sequences" or "escape codes".  If followed by properly formatted pre-defined codes, the terminal would interpret the characters as a command rather than as characters to display on the screen.

Second generation video terminals provided the ability to position the cursor at arbitrary locations on the screen, to change the characteristics of individual characters, such as blinking, bold, underlined, etc.  With each successive generation of video terminal, more features were added, including a choice of fonts, graphics symbols, changing screen resolution, and colors.  These features were selected by the output of special sequences of characters to the terminal.  The most common mechanism was to start the sequence with the [[ASCII]] escape code (ASCII value 27), hence they were called "escape sequences" or "escape codes".  If followed by properly formatted pre-defined codes, the terminal would interpret the characters as a command rather than as characters to display on the screen.

Video terminals supported maximum speeds of 19,200 baud (about 1,920 characters per second).  The most popular terminal model was the VT100 from [[Digital Equipment Corporation]], whose escape sequences became somewhat of a standard in the early days of personal computing.

Video terminals supported maximum speeds of 19,200 baud (about 1,920 characters per second).  The most popular terminal model was the VT100 from [[Digital Equipment Corporation]], whose escape sequences became somewhat of a standard in the early days of personal computing.