Edited sentence: Cable companies are barred from doing this to channels that are also over the airwaves broadcasts, but the Federal Communications Commission (FCC) has declined to enforce this for other channels.Expansion hard drive available from only one vendor.Like all third party devices using CableCARDs with the exception of one commissioned by the cable companies, there is no support for 2 way communication known as Tru2way needed for accessing a cable company's on demand features or switched video.Like the Series 3, the Series 4 has no support for recording analog video sources such as those from cable or satellite set top boxes.Like the Series 3, upgraded storage is possible with an external hard drive but only "My DVR Expander" from Western Digital is compatible with the Tivo.Limited ability to share videos in the home.Limited video buffer.Many cable companies including Time Warner and Comcast have marked video in such a way that the multi-room viewing and TivoToGo features will not work.No 2 way communication with cable companies.No internal wireless support.No support for analog input.Phone modem support has also been removed.Rather than use the copy method that Tivo software currently employs, multi-room viewing would be possible if the Series 4 supported the streaming video method that cable company DVRs use.Some shortcomings of the Series 3 were not addressed in the Series 4:.Such video does not have the limitation on multi-room video or TivoToGo features.The Series 2 has inputs for recording video via composite or s-video inputs.The latest Satellite and cable DVRs have 60 to 90 minute buffers so that a show can be replayed further back than the Series 4's limit of 30 minutes.This is unlike many DVRs that support external drives from a wide range of manufacturers.Two way communication could be achieved using open standards such as those of the internet, but Cable companies prefer their proprietary approach for this.User may add on Wireless G, Wireless N or phone modem adapters