accumulator with carry to memory, multiply (producing a 22 bit signed product), skip if equal, skip and rotate, bit clear, bit set, and bit complement. Another instruction in this group was to display a bit map, to represent a character or other data, on the built-in CRT display screen. Half-word class - instructions operating on the lower or upper six bits of a word. These included load half, store half, skip if halves are different, Set - moves data from any memory location to one of the locations 1 through 15. Sample - reads one of the sixteen 8-bit analog to digital converters and places the signed value in the accumulator. The first eight A/D channels were dedicated to control panel knobs to allow interaction with a running program by the user. The instruction could either hold the computer till a conversion result was ready, or allow more instructions to be executed provided they didn't rely on the contents of the accumulator, which would be overwritten by the A/D conversion value. Display - draws a pixel on one of the CRT displays at a specified location, optionally indexing a register. Index and skip - adds one to one of the memory locations 1 through 15, and skips if a 10-bit overflow occurs. Operate class, used for input/output operations. These included set a bit on one of 14 output lines, read the keyboard, or read the left or right switch bank. Tape class, with opcodes to position the tape, read or write to the tape, and to check the tape against memory. Control panel The LINC control panel was used for single-stepping through programs and for program debugging. Execution could be stopped when the program counter matched a set of switches. Another function allowed execution to be stopped when a particular address was accessed. The single-step and the resume functions could be automatically repeated. The repetition rate could be varied over four orders of magnitude by means of an analog knob and a four-position decade switch, from about one step per second to about half of the full speed. Running a program at one step per second and gradually accelerating it to full speed provided an extremely dramatic way to experience and appreciate the speed of the computer. LINCtape A noteworthy feature of the LINC was the LINCtape. It was a fundamental part of the machine design, not an optional peripheral,