It was a very wise person who once said that digital data is not real until it exists in at least two places. Craig Anderton looks at the obvious, and sometimes not so obvious procedures involved in backing up data.

The importance of backing up all essential data is beyond question, but it isn't as simple as it was in the days of 20Meg hard drives, where all you needed was 20 or 30 floppies to do the job - so here are some practical tips on backing up data before you're backed into a corner.

• Incremental Backups: Several computer programs can back up a hard disk incrementally (after creating the first backup, subsequent backups save only the changes that occurred since the previous backup). With some programs, the backup disk(s) contain a directory of files that must be updated after backing up. If you back up to two or more Syquest (or equivalent) removable cartridge-based hard drives, try using a floppy for the first disk of a backup set. This will usually contain the directory, and it's easier to mount and unmount a floppy to update the directory than wait for a cartridge to spin down and spin up to speed.

By the way, every now and then I back up my hard disk to a second set of Syquests the old-fashioned way — dragging files over manually. If you encounter problems during the incremental backup process (which can happen), you're left with a corrupted backup disk in some proprietary format; you usually cannot recover individual files. Having the other set of conventional backups provides a last resort.

• Sloppy floppies: I don't trust high-density (1.4Meg) disks for long-term storage; I've had too many bad experiences, even with brand-name, high-priced disks. Double-sided, double density disks seem to be much less fussy.

• Data compression works: I use Stuffit for the Macintosh because it has never failed me, saves loads of space and is a de facto standard. It's essential for archival storage to floppies.

Incidentally, saving a sequencer file as a Standard MIDI File can also compress data, typically by 30 to 40%. However, you will lose data not specified in MIDI, such as MIDI Time Piece interface assignments and 'notepad' notes.

• The TC Solution: Some telecommunications (TC) networks allow each user a certain amount of free storage each month. If you're working on something whose loss would be catastrophic, save it to the network as a tertiary backup source. This works well as insurance for works in progress and is great for work done 'on the road.'

• Battery Assault: Beware of the batteries in memory cartridges. Many cartridges (like the kind that store synth patches) contain internal batteries and these can fail. Keep some small, removable labels handy and mark down the date when a cartridge went into service (or when a battery was replaced), and affix it directly to the cartridge. This helps keep track of when batteries need to be replaced. Of course, you might have saved the cartridge contents to a SysEx storage device or program, just in case the battery fails unexpectedly, or the cartridge is damaged...

• SysEx storage: Decide on one SysEx storage medium and stick with it. These days, just about anything with a disk drive seems to offer the option of saving SysEx data. However, these non-dedicated machines may have limits on the file size they can accept, and with SysEx files taking up more and more space, you might be better off springing the extra bucks for a dedicated unit with lots of storage capacity. Various computer programs can also store and send SysEx, but having a dedicated device 'on-line' at all times may be preferable.

• Multitrack digital recorders for storage: If you do a lot of sampling, you probably have a collection of DATs or other tape sources of raw sounds that you've edited and shoved into a sampler. With a machine like ADAT, you can record sound sources into one track of the machine (two for stereo). With eight 40-minute tracks, that works out to over five hours of mono archives.

• Giving it away — the ultimate backup: This solution isn't for everybody, but often when I come up with some really cool samples, I see if anybody's interested in distributing them commercially or at least send a bunch of copies to friends. Once the samples go into the hands of lots of musicians, you have the ultimate in off-site backup.

Speaking of which... no-one likes to contemplate the possibility that everything they own (including data) could be wiped out in seconds from fire or other disaster. See about arranging a 'data exchange' program with a friend or two, where you'll look after some of their disks if they'll look after yours. Another option is a safe deposit box (although if it's important to get at the data in case of your death, bear in mind that sometimes safe deposit boxes are then sealed and require legal measures to be opened).

• Managing dual floppy backups: When backing up data from a sampler to floppies, I use two sets of floppies and alternate saves to each set. Sometimes it's confusing as to which is the current set, but here's a ridiculously simple solution (which I mention just in case some of you are as slow as I am sometimes): write-protect the current set as soon as you've made the backup, then write-enable the previous set. Next time, you'll know which set to use.

• How much backup is enough? People often ask how often they should back up. The answer is simple: back up whenever you've done something you don't want to lose. I always keep a temporary backup floppy around so that if the time isn't right to go through the incremental process, I can at least save to something until I do the official backup.

• The big hard disk: A lot of you have a 40 to 100MB internal drive for your computer and an outboard, gigantic gigabyte disk drive for digital audio. Create a backup partition in your big drive and back up the internal drive contents to it. With a 1.2 gigabyte hard drive, you probably won't miss a 60 or even 100MB partition.

• Beware of tape: DAT tape drives are becoming affordable and are a great way to back up huge piles of data like digital audio files. But remember that tape is tape, and no-one really knows exactly how long data will stick to a DAT or remain in a floppy. Every five years or so it's probably a good idea to re-back up data to a new DAT or floppy.

• Be kind to your data: Remember that removable cartridges, floppies, backup tapes and even magneto-optical cartridges are fragile. Treat them with care and caution.

That's all for now. Until we meet again, may a successful backup be the last thing that happened before your hard disk crashed!