Analog TV systems global map, with System M in red.
CCIR System M,[1][2][3] sometimes called 525–line, monochrome NTSC, NTSC-M, or CCIR-M,[4][5] is the analog broadcast television system approved by the FCC (upon recommendation by the National Television Systems Committee - NTSC)[6] for use in the United States since July 1, 1941,[7][8] replacing the 441-line TV system introduced in 1938.[8] System M comprises a total of 525 interlaced lines of video, of which 486 contain the image information, at 30 frames per second. Video is amplitude modulated and audio is frequency modulated, with a total bandwidth of 6 MHz for each channel, including a guard band.[9]
Strictly speaking, System M does not designate how color is transmitted. However, in nearly every System M country NTSC is used for color television. This combination is called NTSC-M, but usually simply referred to as "NTSC", because of the relative lack of importance of black-and-white television. In NTSC-M and Japan's NTSC-J, the frame rate is offset slightly, becoming 30⁄1.001 frames per second, usually labeled as the rounded number 29.97.
The main exception to System M's being paired with NTSC color is Brazil, where PAL color is used instead, resulting in the PAL-M combination unique to that country. It is monochrome-compatible with other System M countries, but not compatible with other PAL countries, which use 625-line based systems.
Between 1970 and 1991 a variation of the SECAM color system, known as SECAM-M, was used in Cambodia,[13] Laos, and Vietnam (Hanoi and other northern cities).
NTSC — dominant color system used with System M, so much so that System M is often referred to as "NTSC". Much of the information in the NTSC article is actually about System M.
