Screen formats are determined by the specific aspect ratio of the screen. Aspect ratio is the fractional relation of the width of a video image compared to its height. The two most common aspect ratios in home video are 4:3 (also known as 4x3, 1.33:1, or standard) and 16:9 (16x9, 1.78:1, or wide-screen). All the older TVs and computer monitors you grew up with had the squarish 4:3 shape--only 33 percent wider than it was high. On the other hand, 16:9 is the native aspect ratio of most HDTV programming; it is 78 percent wider than it is tall, or fully one-third wider than 4:3.
Also referred to as 4:3, Standard Definition, NTSC or Academy. This aspect ratio is becoming the aspect ratio of the past as 16:9 HD (High Definition) is becoming the new medium. Many classic movies were made in this aspect ratio.
The 4:3 ratio for standard television has been in use since television's origins and has been used for many computer monitors. 4:3 is the aspect ratio defined by the Academy of Motion Picture Arts and Sciences as a standard after the advent of optical sound-on-film. By having TV match this aspect ratio, films previously photographed on film could be satisfactorily viewed on TV in the early days of the medium (i.e. the '40s and the '50s). When cinema attendance dropped, Hollywood created widescreen aspect ratios (such as the 1.85:1 ratio mentioned later) in order to differentiate their industry from the TV.
Also referred to as High Definition, HDTV or Widescreen. This is the international standard format of HDTV as used in the United States, Australia, Japan and Canada as well as in Europe on satellite and non-HD widescreen television (EDTV) PALplus. The 1.78:1 aspect ratio was the compromise between the 35 mm US and UK widescreen standard (1.85:1) and the 35 mm European widescreen standard (1.66:1)
This is now a standard aspect ratio in the USA and all HD projectors (720 or 1080) natively project at this Aspect Ratio. This is also one of the most popular choices for home theaters and media rooms when sports and gaming outweighs movie watching.