Has anyone ever wondered what set top boxes do?

In most households and apartments today, whether they be on cable or broadcast, you most likely have a set top box.  Everyone knows we switched to DTV for broadcast television a few years back. Why did we switch, and what does the box do?  During the summer of '09, you had to start using a converter box to get signal over the air if you had an older TV.  Those boxes cost money. Who is paying for this stuff?
Up until the summer of '09, we were using a broadcasting system as it was developed in the 40's and 50's. Back then, there were plans for many more stations in both VHF (very high frequency) and UHF (ultra high frequency). Each station got 6 MHz of bandwidth to broadcast programing.  Back then, the regulators picked prime bandwidth for broadcasting so you could have more people served per station.  Fast forward to modern times. Things did not work out as well as they had hoped. There were far fewer broadcast stations than they had planned, and therefore, there was a lot of wasted air waves.  Other companies wanted to use the wasted bandwidth for other purposes.  So they came up with a plan. They were going to move all of the tv broadcasts to digital, rearrange the tv stations so they were closer together on the EM spectrum, and then use the cleared up space for other technologies, which would pay for the transition.

Old televisions, of course, would not be able to pick up a digital signal, and it did not know where the stations were because they changed location in the EM spectrum.  They fixed the problem by making a box that had a  digital tuner for the new TV broadcast, that would piggy back on the analogue tuner inside a tv.  Also, if you think this DTV conversion is only a USA thing, then I've got news for you.  Below is a map of the world with an overlay of DTV transition. As you can see, most of the world is still switching to the new standard. I borrowed this image from wiki commons.