The cable TV box. Although impossible to rest on "top" of a flat panel TV set and often located several feet from the TV no matter what type is used, the set-top box (STB) term comes from the early days when cable boxes usually rested on top of CRT-based TVs. Satellite TV uses a similar device; however, rather than a "satellite set-top box," it is officially known as a "satellite TV receiver."

For analog service, set-top boxes descramble the premium channels and manage the higher channel numbers old TVs do not support. For digital service, they decode the MPEG-based digital signals, decrypt the premium channels and store and display the program guides with the channel numbers assigned by the cable provider. "HD set-top boxes" offer high-definition signals in addition to standard definition (SD).

Set-top boxes that convert digital signals broadcast over the air to analog for non-digital TVs are called "converter boxes" (see TV converter box). See HDTV and MPEG.

Built-In DVR
A digital set-top box may have a built-in hard drive for pausing, rewinding, recording and playing back TV programs. Stand-alone DVRs, such as the HD models from Tivo, perform the digital decrypting and decoding with plug-in CableCARD modules that move the cable company algorithms from the set-top box into their units. See CableCARD and DVR.

Internet Access
Although most cable companies offer TV and Internet service, the traditional set-top box does not provide Internet access. Where it enters the house, the cable is divided into two by a small, passive device called a "splitter." One line goes to the set-top box, and the other is fed to the cable modem. See hybrid set-top box and cable modem.