After WW II the telecommunication in the US where operative. Of this reason they where able to develop the first color-tv system in the 1940's. England and West Germany wanted a system with better quality and made PAL. Because of the rebuilding of Europe after World War II this system where not operative before the 1950's. At the same time french engineers worked on developing their own system: SECAM. Most european countries and the british colonies used PAL. France, french colonies and the Sovjet union used SECAM. USA, Japan, the Philipines and Taiwan used NTSC.

NTSC: NTSC is an acronym for National Televisjon Systems Committee, and this system mainly is used in Japan and USA. The system where developed during the 1940's. The intentions where that this should be a black/white system. The engineers discovered a method to add color with the method Chrominence signal. A beam is used to enlighten phosphor on the rear side of the screen. A picture consists of two parts (od an even lines) where each second line is displayed at the time, first the od and then the even lines. When this is done twice (both lines are filled) a still-image is created. This is done 30 times a second. Because two lines are refreshed 30 times a second the refresh rate for this system is 60 Hz.
Data:
30 pictures per second
525 vertical lines (480 visible)
60 Hz refresh rate


PAL: PAL is an acronym for Phase Alternating Line and is used in civilized areas, such as Europe and China. The PAL system is using the same technique as NTSC. The main difference is a bit slower refresh rate of the screen with a much better picture-quality. Developed in England and West Germany in the 50's.
Data:
25 pictures per second
625 vertical lines (585*240 visible)
50 Hz refresh rate


HDTV: HDTV is an acronym for High Definition Television, and is capable of showing up to 5-6 times as much details as modern tv-systems. This system is supposed to give the same picture-quality as a 35 mm film. NTSC is using 525 vertical lines while HDTV is supposed to have up to 1000 lines. This will give a larger area which the signals are shown and a much better quality.