The X1 designation refers to several different cable boxes issued to customers of Comcast's Xfinity home services. These boxes are produced by a number of manufacturers and may or may not include digital video recording capabilities.
Comcast uses the X1 Entertainment Operating System name to refer to its user interface for On Demand and in-home recording and streaming system. The primary models used by Comcast to run the X1 system are the Arris XG1, Pace XG1, Pace RNG150N P2 and Samsung RNG150N. Of the four cable boxes, the XG1 models have DVR capability while the other two do not. Comcast has also released the Pace Xi3 cable box in some test markets that has no DVR capability and can only output signals through HDMI.
The primary difference between the DVR-capable X1 cable boxes and other boxes is that the DVR-capable boxes can record live video. In addition to allowing them to record programming for later viewing, this allows the DVR-capable boxes to pause live programs during viewing. While the RNG150N and Xi3 cable boxes can schedule a recording and stream recorded programs from a DVR-capable box, they cannot be used to pause live television. Some other features of the X1 platform are also only available when using a DVR-capable cable box, including several of the X1 apps.