Today we're going to take a look at what is a surprisingly complicated area for earthlings ? that of CD-drives and all that surrounds them.

CD-Drives, at their outset in the 1980s, represented a huge step forward for computing. They were the first non-magnetic recording media available, and therefore rumoured to be nearly indestructible, and inordinately inexpensive to produce.

We know today that, of course, CDs aren't indestructible, and in fact, can be particularly fragile in the wrong circumstances. It DID however turn out to be true that CDs were very inexpensive.

So what are they? A CD is simply a sheet of light reactive metal coated in clear plastic. It contains the zeroes and ones that represent computer data, as we've discussed previously, only instead of being represented by the magnetic poles as in magnetic devices, they are simply represented by different burn "marks" on the light reactive metallic sheet. The data is retrieved and written to and from the surface of the CD by a class-3 laser built-in to the CD-drive.

In the late eighties, class-3 laser CD-drives started to be introduced into PCs, by the mid nineties they were commonplace, and now they are recognised as the main delivery mechanism for software and applications, media products and games.

There is much confusion over the different types of CD-Drive available, so here to clarify is the list, and a short explanation of each:

1. CD-ROM Drive (Compact Disc - Read Only Memory). Can read CDs, but not DVDs and has no CD writing capability;

2. CD-RW Drive (Compact Disc - ReWritable). Can read CDs, but not DVDs, and has the capability to "burn" (ie write) CDs with data and/or music directly from your PC Hard-Drive or another CD;

3. DVD-ROM Drive (Digital Versatile Disc-Read Only Memory). Can read CDs and DVDs, but has no write capability for either technology;

4. DVD+/-RW (Digital Versatile Disc Plus/Minus ReWritable). Can read CDs and DVDs and has the capability to "burn" (ie write) CDs and DVDs with data, music and DVD movies directly from your PC Hard-Drive, another CD or another DVD;

To confuse us here on earth even more, there are "combination" drives that mix some of the capabilities (i.e. you can get a DVD-ROM/CD-RW drive that reads DVDs, but cannot write them, but can read and write CDs). The good news is that these capabilities are usually clearly spelled out when you buy your PC, in the specification, though they may only use the acronyms shown above.

Over the next couple of weeks, I'm going to explore the whole re-writable capability and try and spell out what this means to us as earthlings. For now though, let's take a look at some common problems, and some definite do's and don't with CDs and CD-Drives in general.

Firstly, let's deal with health and safety. There are few components on a PC that can cause you any lasting physical harm. One of the few that can is the class-3 laser in your CD-drive. It is likely that you won't be able to gain access to the actual laser anyway, but it is as well you know that, though classified as class-3, which is the highest "safe" class of laser, and there are probably readers who know more about this than me who would say they are completely safe, nevertheless I would still advise that you steer clear of looking directly at it should the possibility present itself.

If the casing gets damaged around the actual module (highly unlikely, but possible), then the module should be destroyed immediately, and replaced.

CDs themselves, though robust, are not as indestructible as first thought. In fact, they can be quite easily damaged if not cared for. Always keep them in some kind of cover, and, though the underside is the one that's read by the laser, writing or scratching the top, can ? and frequently does ? damage the data content. Therefore be extremely careful.

You should never try and force a CD-drawer closed or open, as this will damage the motorised mechanism and render the CD-drive unuseable.

Next up: CD-RWs, and the whole CD burning capabilities.