Component and composite audio-visual connection cables both transmit video via an analog signal. That's where the similarities between the two formats end, though, because old-style composite cables are no longer supported by most devices. The newer component cable format was designed to work with modern high-definition devices. However, even component cables have had their day -- high-resolution HDMI is now typically the connection of choice for the latest generation of audio-visual equipment.
A composite video cable -- also known as an RCA or "yellow plug" cable -- is an old standard that transfers a video signal through one cable and connector. It doesn't support HD content or progressive scan images. Because the video signal is forced to travel through a single cable it is heavily compressed, losing much of its resolution and picture clarity. The cables also suffer from radio frequency interference, which further degrades picture quality.
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Component video splits the video signals into three cables -- green, blue and red -- with each transmitting a specific component of the video signal. The green cable (also called Y) transmits the brightness information of the signal. The blue and red cables (called Pb and Pr, respectively) transmit the blue and red components of the picture's color. Green components are inferred by a combination of all three signals. Since component video is spread across three separate cables, it does not need to be as compressed as composite video, allowing support for HD resolutions as high as 1080, as well as progressive scan images that create smoother images with more defined edges.
Composite video is a dying technology, because it can't support HD video signals. When given the option, go for component over composite every time times, because this connection will always provide a better picture at higher resolutions. The only practical use for composite video today is when using older equipment, such as older video game systems or VCRs, which do not support the component video format. Because of this, some new HDTVs include at least one composite video input to make them compatible with old equipment.
Component cables initially replaced composite as the de facto analog video cable, thanks to its improved picture quality and HD support. Nearly all HDTVs made today have at least one set of component inputs. Component video is also supported by most video game consoles, DVD players, digital video recorders, cable set-top boxes and Blu-ray players.
Component video cables are analog, just like composite cables. And also like composite cables they have inherit limitations that are tied to the analog format. Analog cables transmit their signals via waveforms, digital cables transmit their signals the same way a computer transmits data -- through binary code that is decoded by the display device into a viewable picture. Because they travel via waveform, analog signals are susceptible to interference from radio waves and other electronic signals from nearby equipment. Analog signals also have less bandwidth than digital signals, which means increased compression that can negatively affect picture quality. Although less noticeable with component than composite, signals transmitted via component cable will not be as clear as signals transmitted digitally via cables like HDMI and DVI.