Editing LINC (section)

== Text display ==
[[Image:Lincm.png|right|thumb|130px|The capital letter M as it was displayed in a 4 by 6 character cell on the LINC screen]]
The LINC hardware allowed a 12-bit word to be rapidly and automatically displayed on the screen as a 4-wide by 6-high matrix of pixels, making it possible to display full screens of flicker-free text with a minimum of dedicated hardware. The standard display routines generated 4 by 6 character cells, giving the LINC one of the coarsest character sets ever designed.

The display screen was a CRT about 5&nbsp;inches square which was actually a standard [[Tektronix]] oscilloscope with special plug-in amplifiers. The special plug-ins could be replaced with standard oscilloscope plug-ins for use in diagnostic maintenance of the computer. Many LINCs were supplied as kits to be assembled by the end user, so the oscilloscope came in handy.

The CRT used a very-long-persistence white or yellow phosphor, so that lines and curves drawn point-by-point at a relatively slow speed would remain visible throughout programmed drawing loops that frequently lasted half a second or more. The y-axis displayed both plus and minus zero as different values, unnecessarily reflecting the fact that the LINC used [[ones' complement]] arithmetic. Programmers quickly learned to move any negative displayed data up one point to hide the artifact that otherwise tended to appear at y=0.

Notoriously, a tight loop that displayed points repetitively in one place on the screen would [[Screen burn-in|burn a permanent dark hole]] in the delicate phosphor in well under a minute; programmers had to be ready to hit the Stop lever fast if a very bright spot suddenly appeared because of a programming mistake.