M (videocassette format)
M is the name of a professional analog videocassette format created around 1982 by Matsushita and RCA. Developed as a competitor to Sony's Betacam format, M used the same videocassette (and the same oxide-formulated magnetic tape stock) as VHS, much the same way that Betacam was designed to take advantage of cheap and readily available Betamax videocassettes, Like Betacam, M recorded component video and used a much faster linear tape speed. A cassette that would yield 120 minutes on a VHS VCR at SP speed would only yield 20 minutes on a M VCR. The  format was called "M" due to the shape of the threading path of the tape around the helical scan video head drum, which resembles a letter M. (This is also how the U-matic format got its name, for its U-shaped tape path in the VCR.) The M-shaped tape path was retained from VHS. An example M VCR is the Panasonic AU-300. M had a similar 4-head recording system to Betacam, but the chrominance signals were recorded as two FM subcarriers of the main chrominance track FM carrier. M was also marketed by Panasonic (a division of  Matsushita) and Ampex under the Recam (REcording CAMera) name. M was succeeded in 1986 by the MII format developed by Panasonic, using a similar-sized cassette with completely different signal processing and a metal-particle tape formulation.