There are certain sayings that always ring true. Never walk away from a computer without saving all open files. Always buy more memory than you think you will need, and the same for disk size. Anyone who has used a computer for more than five minutes would disagree. But there was a time - not all that long ago - when machines crashed once or twice an hour. Those days are, for the most part, behind us, but it is not good to assume computers will work without a problem for ever. The question of backup is simple: What would it mean to you if you lost all your work? There is little hope for you if you look at that frivolously. Backup today is a particularly difficult problem because we keep getting bigger hard disks. They come with the computers and then we go out and buy more. How do you backup gigabytes and gigabytes of data? You can only do it on to more disks. You may want to put it on tape, but that is more of an enterprise solution where keeping records is more important than immediate access. Prosoft Engineering's Data Backup, for the Macintosh operating system, is about as good as it gets. It is simple to use, although you may want to be careful how you set it up. There are a lot of really useful options and you need to understand what they are. The options are 'simple copy', 'clone', 'versioned', 'full', 'incremental' and 'synchronise'. Each one of these does something slightly different and you need to know what you want. If all you want is to make copies of important files, the option 'simply copy' will do. If you want to copy an entire bootable system, then you need to set it up for 'clone'. The company just released an upgrade that allows it to run with Apple's latest Mac OS upgrade called Tiger. The interface is wonderfully simple and easy to use. You may want to give the whole idea of backup some thought, of course. You should plan to get all the disks named and in the right places. It can take a long time to make a backup, particularly the first time. It will run in the background, however, so it should not interfere with what you are doing too much. It amazes me that people still trust computers not to fail. When was that ever true? Backup is necessary and this software costs nothing compared with what you will pay if you lose everything. Think about it.