IMLAC Corporation was an American electronics company in Needham, Massachusetts, that manufactured graphical display systems, mainly the PDS-1 and PDS-4, in the late 1960s and 1970s.

The electronics included a simple 16-bit minicomputer, 8-16 kilobytes of magnetic-core memory, and a display processor for driving CRT beam movements.

This automatically gave it a much bigger set of programming tools, but it too was usually driven by applications running on larger PDP systems.

The CRT electron beam moved freely in X and Y position and angle under program control to draw individual sloped lines and letter forms, much like the pen-on-paper motions of a pen plotter.

Vector displays were good for showing data charts, modifying line drawings and CAD diagrams, tumbling 3-D wire-frame shapes, editing text, laying out printed pages, and playing simple games.

But they did not handle colors, images, filled-in areas, black-on-white screens, or WYSIWYG fidelity to the fonts of professionally printed text.

The competing lower cost Tektronix 4010 graphics terminal used an alternative storage tube CRT technology which required no continual refresh and hence no local computer display memory at all.

But like an Etch A Sketch, the accumulated image could be modified or moved only by flash-erasing the entire screen and then slowing redrawing everything with data resent from some large computer.

This scheme handled arbitrary fonts, extended character sets, and even cursive right-to-left languages like Arabic.

If the system was to be used mainly for graphics, the monitor could be installed with an unstretched grid leaving ends of the screen permanently unused.

Code for line drawings and overall layout was generated on the fly, by programs running on the local minicomputer or on a large remote computer.

The PDS-1's built-in minicomputer[26] was needed for responding to user keyboard and light pen interactions quickly, without delays in talking to a remote timeshared large computer for help.

The PDS-1 electronics were built from 7400 series low-density TTL integrated circuits, with only a dozen logic gates or 4 register bits per DIP chip.

The software used a quick Bresenham method to compute intermediate points for sloped lines without doing multiplies or divides.

If a long vector program was mistakenly run on a basic machine without that option, the display processor could go wild and potentially burn the monitor phosphor or deflection amplifiers.

The DNLS was used on several PDS-1s at several ARPANET locations, and was the main inspiration for the Xerox Alto's overlapping window system.

[29] Imlac display systems were bundled into various larger commercial products involving visual design and specialized software.

[30] Some simple applications such as text editors were entirely coded in Imlac assembler and could run without much involvement with a larger computer.

But most graphics applications required strong floating point support, compilers, and a file system.

PDS-1 use was held back for several years by not having a standard program library supporting animation or interactive drawing and dragging of objects.

Freeway Crossing, an early predecessor of the popular arcade game Frogger, was created on a PDS-1 as part of a psychology experiment in 1971.

Later, up to 8 players ran on PDS-1 stations or other terminals networked to the MIT host PDP-10 computer running the Mazewar AI program.

The density, capacity, and price of computer memory have improved steadily and exponentially for decades, an engineering trend called Moore's Law.

[35][36] And by easily programmed personal workstations with raster graphics such as the Terak 8510/a UCSD Pascal machine and the high performance PERQ Unix system.

[37] An update version of this emulator can be obtained from the GitHub repository of the Seattle-based Living Computers: Museum + Labs.