About Field and Mode Terminals

When the terminal was introduced in the early 1970s, it replaced the teletype, a hardcopy output device. Initially, terminals were called "glass teletypes" because they literally replaced the hardcopy from a teletype with a screen display.

As computer technology became more advanced, terminal manufacturers added new display capabilities to their terminals, such as low intensity, reverse, underline and blinking options. Each terminal manufacturer implemented different methods of displaying these attributes, resulting in two standards: field and mode operation.

Field Terminals

On a field terminal, attributes (such as start and stop reverse video) occupy a position on the display with the attribute continuing until it's turned off or changed by another attribute.

For example, turning on reverse video at screen position 1,1 will "flood" the screen with reverse video because there is no other attribute to disable reverse.

The exception to the rule for field terminals is low intensity - this attribute operates using the mode paradigm.

Field terminals emulated by ZTERM 2000 are Alpha Micro AM-62A, Alpha Micro AM-62C, Contemporary Cybernetics CY-350, Wyse 50, and Wyse 350.

Field terminals are much more complex to emulate than mode terminals and therefore the performance of ZTERM 2000 will decrease slightly when emulating one of these terminals.

Mode Terminals

On mode terminals, attributes don't take up a screen position and they don't take effect until the attribute is enabled and the host system sends some characters to be displayed in the selected attribute.

Mode terminals emulated by ZTERM 2000 are ANSI and DEC VT-100.