I KNOW computer mice are only a small, unimportant part of today's systems, but I'd like to know more about computer mice. In the past, many of the mice I've used with my PCs have always had compatibility problems with several programs on my system. Isn'tthere a standard mice makers have to follow? And how expensive are good mice? JAY MICHAELS Discovery Bay In today's world of graphics-based intuitive computing, mice are far from ''unimportant''. The devices, made popular by the Apple Macintosh and now by Microsoft's Windows program running on PCs, have become an integral part of desktop technology. No Windows user would be able to survive long without one, and no sane Mac user would even switch on his machine if a mouse was not attached to it. If you buy an Apple Macintosh, you get a mouse as part of the deal. That is also true with many PC compatibles today. They are loaded with Windows and have a mouse. If you need a first mouse for a PC or want to replace an old one, you can expect to pay between HK$100 and HK$1,500. To make the choice, you should consider three things: the feel of the mouse; the reliability of its hardware; and the flexibility and compatibility of its ''driver'' software (the program that comes with the mouse to integrate it with your computer). Microsoft sells lots of mice, but they aren't cheap. The new Microsoft Mouse for the PC sells for more than the average mouse - US$109 (HK$850) - and claims several justifications. Firstly, compatibility. Microsoft makes the foundation software in almost all PCs - DOS and Windows, as well as many popular application programs. Microsoft has also been one of the most popular sources of mice for years. So, Microsoft's drivers have become the standard. When you buy a PC mouse, you want it to be ''Microsoft-compatible''. Secondly, the Microsoft mouse's driver offers more flexibility. There are lots of choices you can make on screen to affect how the cursor behaves: whether it is big or small, leaves a trail as it moves (to make it easier to find on a poorly lit screen),''snaps'' to the nearest Windows command choice, jumps to the middle of the screen, and the like. These are fun to experiment with, but it is not something many people make regular use of. The Microsoft mouse is also built from ''high quality components''. These are claimed to make it less likely to fail. Finally, the new Microsoft mouse, which has a ''J'' shape, is supposedly ''ergonomically correct''. That is, it has been designed to fit the hand comfortably and its use should result in fewer repetitive strain injuries. Logitech is the other big maker of mice. Many of the mice you find bundled with new PCs are from Logitech, even when you do not see the Logitech name on them. The MouseMan (US$119) competes directly with Microsoft's mouse. It is Microsoft-compatible, has drivers with flexibility like Microsoft's and also claims high quality components. Logitech offers more DOS mice software than Microsoft, with utility programs to customise the mice buttons - giving them functions such as copying information from one program to another - and to add mice menus to programs that normally do not work with a mouse. The MouseMan is designed to fit the hand naturally. In its family of mice, there have even been left-and right-handed versions. Logitech's TrackMan trackball (US$139) is curved even more than the Microsoft mouse, though it only claims to fit right hands.The US$149 MouseMan Cordless mouse feels a lot like the MouseMan, but it uses radio waves to get the movement and clicking across, so you can use it without worrying about tangling a cord. Honeywell's Mouse (US$79) is compatible with Microsoft's, has driver control of cursor speed and sensitivity, and doesn't cost as much as the leaders. Its software isn't as flexible as Microsoft's or Logitech's, nor does its plain design show any ergonomic flair. However, because it doesn't have the roller ball that most mice travel on, it doesn't pick up hairs and dust. Then there are trackballs, devices which look like an upside-down mouse. The Expert Mouse (US$149) from Kensington systems is one example. Its software is Microsoft-compatible (Kensington and Logitech are the biggest names in trackballs), even using the standard mouse driver built into Windows. The software isn't very flexible, though. Logitech's TrackMan is smaller and comes with the same software as the MouseMan. Logitech's TrackMan Portable (US$169) is a compact trackball that hooks on to the side of a portable computer's keyboard. It works well, as does Microsoft's BallPoint Mouse (US$149) - which is also a trackball. Neither is that comfortable or convenient,though - easy to knock off, hard to store, just a general pain. However, they are a necessary evil if you add Windows to a portable and don't have a built-in trackball or a facility with keyboard commands for Windows. A good choice when buying a mouse is to pick up a generic brand from a discount computer shop. If you trust computer stores such as those in Shamshuipo to stock decent products and take it back when there's trouble, you can get a Microsoft-compatible mouse, though without the full software customising and flexibility, for about HK$100, perhaps even as little as HK$80.