Editing Tektronix 4010 (section)

===Text display===
In ''alpha mode'', the 4010 displayed 35 lines of 74 characters. The terminal was "dumb" by standards of the day, lacking various [[Block-oriented terminal|smart terminal]] features like addressable cursor positioning. The terminal also lacked any significant data buffering, and many slower operations could lead to data loss. For example, the carriage return took about 100 to 200 μs, and a screen clear operation much longer than that, on the order of a second. It was up to the host computer to delay further data to avoid it being lost during these refractory periods.{{sfn|Tektronix|1974|p=2-9}}

One peculiar feature was a second margin at the 35th character, allowing lines to be limited between the left side of the screen and that midpoint for margin 0, or that midpoint and the right side of the screen for margin 1. This was useful for mixing graphics and text, or displaying two columns of text.  Switching between the columns was accomplished by moving to the very last line in any given column and pressing line feed on the keyboard. The cursor would then reappear at the top of the next column. There was no attempt to limit drawing to within these borders, so it was up to the host software to ensure that lines remained within the margins by inserting CR/LF characters at appropriate points. Text lines writing to margin 0 would extend the full length of the screen if CR/LF was not sent to wrap before the 35th character, although any data in the margin 1 area on the same line, being written later, would be drawn on top.

The terminals also optionally supported a second character set via plug-in [[circuit board]]s, selecting between them with the ASCII {{keypress|SI}} and {{keypress|SO}} characters.{{sfn|Tektronix|1974|p=2-7}} This was required for the [[APL (programming language)|APL]] language, which used a large number of special characters.