Computers: Hunt the working version: Andrew Brown offers a warning for the unwary

ONE OF THE distinctive habits of computer companies is to sell things that do not work and then charge extra for the version that does. So far as I know, this practice is unique to the computer industry: car manufacturers do not launch sporty saloons which lock the steering wheel at 73 miles an hour and then offer their surviving customers a chance to buy next year's model at a discount.

But software companies, when their products do the equivalent, just quietly release another one.

This tendency is so well-known as to have been converted into a rule of thumb: never buy version 1.0 of anything. But this does not go nearly far enough. For some upgrades are larger than others and go far beyond quiet improvement. These, too, should be shunned at first.

There is a convention in the industry that when you make a really big change in a program, then you increase the numbering by a whole point. Thus, MS-Dos 5 is a huge improvement on 4.01; and Dos 6 has many capabilities missing from Dos 5. But there is a snag. The keen-eyed reader will notice that the predecessor of Dos 5 was not Dos 4, but 4.01. The difference between these versions is that 4.01 worked.

So the rule with version numbers becomes more subtle. The number before the decimal point tells you what a program does: the little number afterwards tells you whether it actually does it. The canny buyer avoids version anything point nought.

I recently tripped over this problem painfully, but only now have calmed down enough to write about it without leaving frothing toothmarks on the desk. In common with anyone who uses communications a lot, I depend on a program called PKzip, which squeezes files to about half their original size. This makes them quicker and cheaper to send over telephone lines and conserves hard disk space too. PKzip has been around for a long time and is completely reliable.

PKzip was recently upgraded to version 2.0, which offers enormous advantages over its predecessor, except that it does not work. This was rapidly followed by version 2.04, which almost works, and versions 2.04b,c,d,e,f, none of which quite work all the time, and now 2.04g.

Version 2.04g is the one that works the way it should. But being a normal person, I do not look at the final letter three places after the decimal point in my software and I recently spent three days, on and off, trying to install a piece of software that had been compressed using 2.04g on a machine with version 2.04e installed.

It is, on reflection, unreasonable to ask software manufacturers, especially small ones, to get their immensely complicated devices working perfectly first time. But the least they could do, when they finally get everything running smoothly, is to make the difference clear in the name.