What's a 'software update' or 'software upgrade'?
DTT decoders are more like PCs than TVs, in that the technology in them is generally much less stable, and the software they contain is in a constant state of evolution. Just as you can download software updates over the Internet to upgrade software on a PC and fix 'bugs', you can do the same with a DTT decoder - except that the required software is broadcast over the air alongside the digital TV signals.

The ideal, of course, would be for all this to take place in the background, without owners of DTT decoders needing to know anything about it (this is certainly what happens on Sky Digital, for instance). Unfortunately, matters aren't that simple in the Freeview world, because only a limited amount of capacity is available to transmit such signals, and the manufacturers of set-top boxes have to share that capacity between them. This in turn means that they only broadcast updates for a particular box at a particular time, and if you miss that broadcast, you may have missed out on being able to update your box (at least until the next upgrade is scheduled).

Most of the latest boxes will alert their owners to the availability of a broadcast update with an on-screen message - in which case, you just need to follow the onscreen instructions - or simply automatically update themselves. However, there are some (generally older) boxes that do neither: instead, you need to look up the details on the manufacturer's web-site, phone up the dealer or manufacturer's help-line, or consult this schedule on the DTG site. However, the DTG schedule is not complete, since - for reasons that idtv.co.uk has never understood - some manufacturers regard information about their software upgrade schedule as commercially confidential.

This situation is clearly unsatisfactory, because in some cases, it puts the burden on the consumer to find out about upgrades rather than on the manufacturer. It's certainly worth checking when you buy a DTT receiver that it has an 'alert' facility to let you know when to upgrade, or does so automatically.