By now you probably have noticed that the and the Pro have the same features and capabilities. They differ in only one area; the amount of storage space. The TiVo Roamio Plus has a 1 TB (terabyte) hard disk drive which can store 150 hours of HD broadcasts or 1,000 hours at standard definition. The Pro features a 3 TB hard disk which can record 450 hours of HD programming and 3,000 hours of shows at standard definition.
The storage of the TiVo Roamio can be increased by adding an external hard drive. The external drive must have an eSATA connection in order to plug into the back of the unit. One word of caution about expanding the TiVo Roamio. The external drive is not a portable hard drive and cannot be used to carry programs for viewing on other TiVo systems. Shows are equally divided between internal and external storage. When the external drive is first plugged into a TiVo, the drive is formatted and all previously contained content will be erased.
The TiVo Roamio Plus DVR and Streaming Media Player has a standard F-type coax connector used for attaching the cable TV feed. This connection is also used for a MoCA (multimedia over coax alliance) network if you will be using that feature. More on that later. Remember, the cable TV connection is only for digital cable TV. No analog signals or antenna broadcasts are supported.
Also for networking is the RJ45 Ethernet connector. While all TiVo Roamio models also have built-in wireless networking, a wired network connection is recommend for streaming video to other TVs in the house or streaming content outside the home. Wireless networking may be able to support one stream but a wired connection is definitely needed if more video content will be streamed.
Here is the WeaKnees TiVo Roamio Comparison Guide.