TV tuner
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A TV tuner is a computer component which allows you to watch television on your computer. Most TV tuners also function as video capture cards, allowing them to record television programs onto a hard disk. Almost all TV tuners can function as FM radios: this is because the FM radio spectrum lies between television channels 6 and 7, and television sound uses the same modulation as FM.
There are two types of TV tuners available: external tuners and internal tuners. External tuners sit outside the computer and attached to the computer, usually by a USB connection. Internal tuners are generally PCI or PCI Express cards that are plugged into a computer motherboard's internal slots. Some video cards also function as tuners.
Most internal tuners do all the signal processing needed to convert a radio signal into an on-screen image; some even make use of direct links to the sound card and video card to bypass the CPU entirely. External tuners may convert the signal into either a video stream suitable for display on the screen, or to an intermediate format such as MPEG; in either case, the CPU is needed to direct the image onto the screen.
There are also TV tuners based on software radio: the tuner only provides basic radio tuning; the signal processing needed to turn the radio signal into an image is handled entirely by the CPU. These tuners are very rare.
TV tuners supporting digital television broadcasts have recently become available; a tuner displaying an HDTV image on a computer monitor is typically much cheaper than a dedicated high-definition television system, but with a smaller physical screen.