CAT (phototypesetter)
The GSI C/A/T (Computer Assisted Typesetter) is a phototypesetter developed by Graphic Systems in 1972. This phototypesetter, along with troff software for UNIX, revolutionized the typesetting and document printing industry. Phototypesetting is most often used with offset printing technology. The GSI C/A/T phototypesetter was marketed by Singer Corporation in 1974 before the company was purchased by Wang Laboratories in 1978. Graphic Systems designed a simple computer front end to print basic text as display type. Full-scale page-composition computing was designed at Bell Laboratories as part of the UNIX project. Features. The C /A/T phototypesetter features: C/A/T optics consist of a rotating wheel to which are attached film strips of master font characters. The wheel's periphery has four such replaceable font film strip sections. A xenon strobe inside the wheel is programmed to flash the characters from the font films through magnification optics to a fiber-optic bundle. The programmable location of the fiber-optic bundle determines the horizontal position of the character image on a scroll of photographic paper or film. C/A/T is a highly addressable phototypesetter with full optics control from computer-generated data. This  precise control of optics and image position made the interface to computer programs reasonably simple. Data is normally transmitted to the C/A/T by paper tape. Some companies created electronic replacements for the paper-tape interface to accommodate direct connection to computer systems. C/A/T has no page layout and pagination capability. It is only a high-resolution printer that puts high-resolution character images onto a photographic medium. Page layout is determined by the typesetting software used to generate the paper tape. History. Bell Labs purchased a C/A/T phototypesetter in 1973 for their engineers who  were developing the UNIX operating system. C/A/T became the de facto standard for UNIX-based typesetting. The early typesetting programs on general-purpose computers displaced special-purpose photocomposition systems. Noteworthy typesetting software created for C/A/T includes troff (1973), which was developed by Joe F. Ossanna at Bell Labs. Brian Kernighan later developed ditroff (typesetter independent troff), which supported the C/A/T and other publishing systems. C/A/T was the workhorse of UNIX printing through the 1980s for shops that could not afford hot lead typography equipment or expensive and proprietary document typesetting systems. High -resolution laser printing, now common in desktop publishing, was not yet available. Graphic Systems did not have the marketing capability to dominate the phototypesetting business. Singer Manufacturing Company around 1975 acquired the rights to market the hardware, including placing the Singer C/A/T logo on the products. Singer continued to support C/A/T systems until 1979. Wang Laboratories bought Graphic Systems in 1978. The phototypesetter was then known as Wang Graphic Systems C/A/T with continued support through the 1980s. Advances in electronic typesetting programs such as ditroff (1979), TeX (1979), and LaTeX (1981–1983) obsoleted the C /A/T phototypesetter. C/A/T continued to be prevalent in many UNIX-based documentation shops until high-quality laser printers became prevalent. Standard error. The output stream standard error (stderr), a standard on many systems for over 40 years, was first created because of this device. Initially, error messages from typesetting software were also sent to the typesetter, wasting time and materials. This prompted the creation of a separate output channel for error messages.