This less-publicized cable digital upgrade by some cable companies is already affecting the range of popular cable channels that typically fall between channels 20 and 90, including TV addict essentials such as AMC, CNBC, CNN Headline News, ESPN, History, MSNBC, MTV, Spike TV, TNT, and the USA Network. Depending on your cable company, these channels may be available only if you have a cable box.

Prior to the digital upgrade, such channels usually did not require viewers to rent an extra-cost cable box in order to view shows. Instead, you could plug your coaxial cable from the wall directly into any of the following:

If you now run your cable directly through any of these devices, you may be affected. .

In some cases, you'll simply be inconvenienced: You'll now need to have a cable box and in order for your device to communicate with the box to change channels, but you'll still be able to view and record analog video.

In other cases, though, you may be out of luck. You might not be able to record or even view your channels. However, companies like TiVo are working closely with Comcast--the cable provider deploying the digital upgrade most widely--to make its legacy devices as compatible as possible.