HP-GL

The language (Hewlett-Packard Graphics Language) appeared in 1977 and became the standard for driving pen plotters. Its commands are short and geometric: PU raises the pen, PD lowers it, PA moves to an absolute coordinate. A drawing is therefore a list of where the pen should go, not a raster of dots — perfect for engineering drawings meant to scale freely.

HP-GL outlived the plotter's heyday and still turns up in CAD export and in cutting plotters for vinyl and textile work. Its successor HP-GL/2 was later folded into PCL. Where PostScript describes a page in areas and fonts, HP-GL thinks in lines, which suits anything that is really drawn rather than printed.