What is a Set-Top Box (STB)?
A digital set-top box may be needed for receiving digital TV broadcasts, because most older TV sets don't have a digital tuner.
An STB is a device that receives and decodes digital television (DTV) broadcasts so they can be displayed on analogue television sets or other display devices, such as computer monitors or projection screens. These can be SD or HD broadcasts, depending on the type of STB you use. In the most straightforward configuration, you simply plug the STB into your existing aerial and TV set, using either a composite, S-Video or component video cable. It will usually scan and find any available channels. The STB then receives the digital stream being broadcast and decodes it so your existing analogue TV can understand it. You can, of course, also connect it to your sound system and VCR.
Basic SD-STBs can cost as little as $100 or so, while HD-STBs usually cost a few hundred dollars more. The price of both types of STB can vary widely, depending on their feature set. As mentioned previously however, there is no point getting an HD-STB unless you have a high-resolution screen to use with it, and even if you do, the lack of HD content means that a lot of the time you will be viewing programs in standard-definition.
Don't let that put you off, though. If you want the ultimate in quality, more HD content is gradually being made available and quite simply, nothing else compares (there are also a number of SDTV and HDTV tuner cards available for PCs and even external USB-based Digital TV receivers for notebook computers).
Inside the box
A typical STB has one or more microprocessors for running the operating system (OS), possibly Linux or Windows CE, PowerTV, JavaOS or any one of a number of small "embedded applications". To the end user, it doesn't really matter what OS is used and usually it is not able to be accessed by the user. A set-top box also includes RAM, an MPEG decoder chip, and more chips for audio decoding and processing. Again, they include everything required and are usually not upgradeable.