Changes

===Flow Control===

===Flow Control===

Because computers could output data faster than even the fastest terminal could accept, a means of pausing the I/O was needed.  This was needed in both directions since a computer with numerous ports taking input from terminals could sometimes not keep up with all of the input.  Mechanical connections usually had control lines that indicated when either end of the line could accept more data.  In the use of dialup lines, there are no individual control lines for flow control.  In such cases, an XON/XOFF protocol is used.  XON and XOFF are ASCII control codes which are reserved to indicate resuming and pausing (respectively) data transfer.

Because computers could output data faster than even the fastest terminal could accept, a means of pausing the I/O was needed.  This was needed in both directions since a computer with numerous ports taking input from terminals could sometimes not keep up with all of the input.  Mechanical connections usually had control lines that indicated when either end of the line could accept more data.  In the use of dialup lines, there are no individual control lines for flow control.  In such cases, an XON/XOFF protocol is used.  XON and XOFF are [[ASCII]] control codes which are reserved to indicate resuming and pausing (respectively) data transfer.

===Echo===

===Echo===

Terminals typically only sent data when a key on the keyboard was pressed.  The computer received the data and then sent the character back to the terminal for display.  The process is called "echo" and provided the ability to hide characters by not echoing characters when the computer software was asking for a password, for instance.  However, the travel time for the characters in both directions, plus pauses when the computer was busy, could tend to make typing more difficult.  Thus, many terminals also included a "local echo" ability where the terminal would both send a character when a key was pressed, but also displayed the character at the cursor position itself.  In this case, the computer had to know about the local echo or else it would still output the character to the terminal after the terminal already displayed it, resulting in duplicating each character.

Terminals typically only sent data when a key on the keyboard was pressed.  The computer received the data and then sent the character back to the terminal for display.  The process is called "echo" and provided the ability to hide characters by not echoing characters when the computer software was asking for a password, for instance.  However, the travel time for the characters in both directions, plus pauses when the computer was busy, could tend to make typing more difficult.  Thus, many terminals also included a "local echo" ability where the terminal would both send a character when a key was pressed, but also displayed the character at the cursor position itself.  In this case, the computer had to know about the local echo or else it would still output the character to the terminal after the terminal already displayed it, resulting in duplicating each character.