encode the character and another slot that caught a locking bar, which locked all the keys in one mechanical movement of the locking solenoid. When the user pressed a key, the pressed key was locked in its down position, and all the other keys were locked in the up position. When the running program read the keyboard, the lock was released, and the pressed key would pop back up. This could have the effect of slowing down typing and preventing even 2-key rollover. This exotic keyboard was abandoned in favor of Teletype keyboards, such as the Model 35 KSR and Model 37 KSR, in the LINC-8 and PDP-12 follow-on computers. Knobs The LINC included a set of eight three-turn potentiometers (numbered 0-7) that could be each be read by a computer instruction. The dial box was a convenient user input device at a time before general adoption of the mouse. For example, one knob could control the scaling of a displayed graph, and another might be used as a cursor to display the actual data value at a point. Text display 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 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 burn a permanent