PUBLISHED : Sunday, 09 September, 2007, 12:00am
UPDATED : Sunday, 09 September, 2007, 12:00am

I have heard a lot about fingerprint readers being built into devices such as notebook computers and PDAs. Do you know if the same technology is available in a mobile phone?

Name and address supplied

DQ: There is such a mobile phone - the Pantech GI100, which you can investigate at www.gsmarena.com/pantech_gi100-806.php. But it is unlikely to interest anybody because it is old and does not include many features we now take for granted, such as Bluetooth.

More interestingly, Japanese electronics manufacturer Sharp is including new technologies that will enable fingerprint-reading on the screens of its mobile phones. Have a look at gizmodo.com/gadgets/cellphones/sharps-next-gen-mobiles-to-pack-fingerprint-reading-touchscreens-239614.php.

Before you get too excited about that development, I suggest caution. Some people have complained a fingerprint reader on a mobile phone should not be on its screen; it will get filthy if a user is constantly touching it.

Just to throw a spanner in the works, have a look at this rather sobering video at www.youtube.com/watch?v=E20lHqbWqN4. Although it takes some effort, it is not impossible to 'steal' somebody's fingerprint, make a latex copy of it then open any lock that depends on that digit's impression. Little is truly safe in this world.

I used to have a Windows personal computer, but I have started using a Mac. Do I need to defrag my hard disk? I used to do it all the time on my PC but I heard somewhere that I won't need to now.

John, Causeway Bay

DQ: According to Apple, you are right: it is no longer necessary to subject a Mac to defragmentation.

Hard drives easily get cluttered with bits of information - including files created, modified and deleted - that are scattered all over the device. This situation forces the PC to search through different parts of the disk to assemble a single file, slowing data recall in much the same way as storing different components of a toaster in different parts of a factory would slow an assembly line. Defrag corrects that condition by putting the information in order, making the computer faster. An article about disk optimisation and fragmentation on the Apple website explains why: docs.info.apple.com/article.html?artnum=25668.

The greatest problem in the old days was the more you added to an existing file, the more fragmented the data became. A file might begin on one sector but subsequent writes to the disk would not be sequential because other files might have been created in between.

Current hard disks are faster and bigger, which allows the Mac operating system to handle files more effectively, says Apple. Better read-ahead, write-behind caching in present hard drives means files are often completely written to disk as if they were new. This, of course, means they use consecutive sectors of the hard disk. Still, utilities for defragging disks on Mac computers are available. I wonder if they are really worthwhile.