A TV tuner obtains a television signal from your cable box, satellite receiver, antenna, or cable connection and converts it to a signal your computer can understand. Media-based PCs that come with their own built-in TV tuners are different from commonplace computers though, and most computers don't come with TV tuners built-in. Most computers can be used to play music, watch DVDs, view pictures, browse the Internet and display email, though. Computers that come with their own media hardware can do much more. If you have a media-based PC you can display movies in HD, play music in surround sound, and show large slideshows of photographs from vacations or adventures.If you have a TV tuner, you can use it to watch and record live TV.
If you have a media center PC or a high-end Windows 7 desktop, you may have an installed TV Tuner. If you don’t, you can purchase a TV tuner from your local computer store or an online vendor. Make sure you get an actual "tv tuner" though; not just a fancy antenna! You can then use Windows Media Center to watch live TV anytime you want. You can also record, rewind, or fast forward television and TV recordings.
When you set up Media Center, you'll work through a variety of screens that help you configure your display, connection, and other data and hardware.This one, shot by the author, shows three ways this computer can connect to a display.

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If you're having trouble installing your TV tuner, refer to How to Install a TV Tuner Card.