Drawing instead of printing
The first computers produced numbers and text, often as printed lines or punched cards. Many problems in engineering and science, though, are naturally pictures: a curve, a map contour, a building plan. A plotter solved this by moving a pen across paper under computer control. For a time it was the main way to get a precise drawing out of a computer, and it came before the screen-based graphics most people know now.
How a pen plotter works
A plotter receives commands from the computer, such as move to a point, lower the pen, draw to another point, and lift the pen. Motors move the pen or the paper, or both, along two axes. Two main designs became common.
A drum plotter wraps the paper around a rotating cylinder. The cylinder moves the paper back and forth for one axis, while the pen carriage slides along the drum for the other. This allows long drawings on a roll of paper in a compact machine. A flatbed plotter holds the paper flat on a table, and an arm carries the pen across it. Flatbeds suit large or special drawings, and could hold different pens for different colors or line widths.
Because the pen draws lines between points, the output is made of straight segments and, with many short segments, apparent curves. This differs from a modern printer, which fills a grid of dots. Plotters were therefore good at lines and poor at shaded areas.
Early machines
Plotters appeared in the 1950s as laboratory instruments for recording results, for example plotting a measured signal against time. Computer-controlled plotters followed. California Computer Products, known as Calcomp, introduced a digital drum plotter in 1959 and became a major supplier. Other companies, including Benson-Lehner, also sold plotters for use with early computers. Exactly which machine was the first plotter driven by a digital computer is hard to state with certainty, and descriptions vary.
In the 1970s, companies such as Hewlett-Packard introduced smaller, less expensive desktop plotters, which put the technology within reach of small firms and university departments.
Engineering and architecture
The most valuable use was technical drawing. Engineers designing aircraft, ships and machines had long drawn parts by hand on paper, and computer-aided design tools in the 1960s and 1970s could generate drawings automatically. A plotter turned the computer’s stored geometry into a drawing the shop floor could read. Architects, surveyors and map makers used plotters for plans, site drawings and contour maps. Electronics designers plotted layouts for circuit boards and chips, which were then used to make masks for manufacturing.
The ability to redraw a design at a different scale, or with a changed dimension, made computer drawing attractive. A drawing could be stored, edited and reproduced without starting again, which saved time even though early software was expensive and awkward.
Plotters and early computer art
Plotters also attracted artists and mathematicians who saw the drawings as a new medium. In the mid-1960s, several people produced abstract images with programs and plotters. A. Michael Noll at Bell Labs created computer-generated pictures in the early to mid-1960s. Frieder Nake and Georg Nees in Germany exhibited plotter drawings in 1965, and are often named among the first computer artists, alongside others such as Vera Molnar in France, who began working with algorithmic ideas around the same time. Exhibitions of computer art took place in the United States and Europe in 1965 and after.
The images typically used lines, repeated shapes and controlled randomness. They were limited by the technology, but they showed that programs could make drawings with a visual character of their own. Opinion was divided at the time on whether this was art at all, and debates about that question continue in a different form with image-making by artificial intelligence.
Other early graphics
Plotters were one road to computer graphics. Another was the screen display built on cathode ray tubes. MIT’s Whirlwind computer and the SAGE air defense system used screens in the 1950s, and Ivan Sutherland’s Sketchpad in 1963 showed interactive drawing on a screen. Screens were fast and interactive, but they had low resolution and left no permanent copy. A plotter produced a durable, accurate drawing, so the two methods complemented each other for years.
Decline
Several developments reduced plotter use. Laser printers and large-format inkjet printers could produce complex drawings quickly, with shading and color, and they needed fewer moving parts. Software improved to the point where drawings were shared as files and viewed on screen. By the 1990s and 2000s, wide-format inkjet devices took over most tasks, though pen plotters survive in some niches, such as art and cutting vinyl with a blade instead of a pen. Some hobbyists build their own plotters, finding value in the look of ink lines on paper.
Why the plotter matters
The pen plotter was the first practical bridge between computer calculation and a physical drawing. It set expectations for accurate computer-generated drawings, and its output helped establish that computers could produce images, not just numbers. The later machines that print graphics, from laser printers to image scanners that capture them, built on that foundation.