An electronic ballast (also known as a solid-state ballast and/or digital ballast) works in a totally different way to the old magnetic ballasts. While the old magnetic ballasts made use of induction to limit the current that can pass, the electronic ballasts switch the power on and off really quickly to achieve the same effect.
Electronic ballasts can be thought of as switching power supplies, that take mains AC and convert it to the high DC voltages needed to strike the arc. As such electronic ballasts are not tied to the mains frequency (50Hz over here), and because of this they can run at higher frequencies (usually 20,000Hz) which eliminates the flicker, hum, headaches and other issues that plagued magnetic ballasts. This coupled with the fact that electronic ballasts are smaller, lighter, programmable and more efficient than magnetic ballasts, means that they are well on their way to replacing magnetic ballasts in fluorescent lighting.
The only benefit that magnetic ballasts have is that they are cheaper (although in my "DIY electronic ballasts" article I show how you can get electronic ballasts for essentially free) and simpler to build (and more resilient, you generally can't dunk an electronic ballast into water and have it work afterwards).
As a general rule electronic ballasts fit into 3 program modes:
The typical place where home users will come across digital ballasts are in those low-energy/eco-friendly lightbulbs, which are a subset of CFLs and usually look like this:
These are known as integrated CFLs, because they have the electronic ballast integrated into the lamp as a single package. Most fluorescent systems have the ballast seperate because it offers the following advantages:
Despite the advantages, integrated CFLs are more popular for homes because of the ease of installation. Integrated CFLs will work in normal bayonet or screw sockets without any modification. Other systems require alteration of the sockets to either 2-pin or the newer 4-pin CFL sockets. I have started to see new homes built with discrete CFL systems, so eventually integrated CFL's will not be the only alternative.
As the main cause of failure on integrated CFLs is the lamp rather than the ballast, we can remove the ballasts from those CFLs and use them with seperate CFL lamps as a discrete system. For more info any my experiences recycling these ballasts have a look at my Recycle CFL Ballasts article.