Comcast Corp. will be the first cable TV operator in the US to unlock online access to a great lineup of valuable cable shows and movies, in an attempt to replicate what's available on television through video on demand. By the end of the year, subscribers will be able to watch popular shows such as AMC's "Mad Men" and HBO's "Entourage" online without paying extra through the "On Demand Online" service.

Other cable companies, including Time Warner Cable Inc., plan to follow in their footsteps.

Access to the online content will be very carefully guarded. At first, Comcast subscribers will only be able to watch the shows and movies on their home computers after being verified by the cable system. It will also be restricted to only those customers who also get their Internet service through Comcast, and not through a phone company or other competitor.

Realizing that this is quite a few hoops to jump through in order to watch content online, Comcast is also working on providing access over competing home broadband systems and well as on the go.

The cable networks themselves, such as HBO, will decide how much they will put online. Some may only put up the current season's episodes, while others could also include archives of past seasons.

Broadcast television networks have been offering full online episodes for awhile now, on both their own sites and sites like Hulu.com. Cable networks have resisted joining in, and are only just now jumping on board.

Comcast subscribers will be able to access the shows and movies through Comcast.net and Fancast.com, and eventually on the websites of the cable networks.