Despite living in a world where hard disks are insanely cheap, and removable media incredibly small, the humble CD doesn't show any signs of being superseded the way it has replaced the floppy disk. Although the CD was originally a read-only medium, the development of rewritable disks has meant that the floppy disk is no longer necessary, besides the fact that its humble 1.4MB is not enough for anything but the simplest of documents anymore. Additionally, the competition in removable media has thinned, with things like ZIP, JAZ and Super Floppy disks no longer being cost-effective or as widely used as CD-ROM drives.

On the other hand, however, it is worth remembering that you can pick up an 80GB hard disk for under Rs.3000- that's equivalent to about 120 CDs. That works out to less than half a cent per megabyte, but blank CDs will still only cost you half of that and rewritables will work out about the same. Add to that the fact that a standard IDE hard disk can read and write at least 60MB per second, compared to only 5MB per second for CDs. Still, the fact remains that CDs are durable, portable, convenient, small and cheap.

Whether you are looking for a cost-effective backup solution, or you just want to share files with your friends, a CD writer is pretty much an essential ingredient of any PC these days. Whatever your reasons, there are a few key considerations to bear in mind when looking at purchasing a burner:

Advantages

• CD media are very cheap
• Recording speeds of 40x let you burn CDs in under three minutes
• Portability
• Compatibility with almost all computers and audio devices
• Long shelf life (theoretically up to 100 years)
• Buffer underrun protection means you can use your PC while you burn
• CDs are more durable than magnetic media such as hard disks

Disadvantages

• May require you to stop using your PC while you burn CDs
• Rewritable disks are slower and more expensive than write-once CDs
• Slow capacity compared to DVD writers, which are becoming more affordable

How CDs work

All three CD disc types (CD-ROM, CD-R, CD-RW) store information in grooves that are 1.6 microns wide (a micron is one one-thousandth of a millimetre; the average human hair is about 50 microns wide). Unlike magnetic storage media, such as hard disks, which store data as polarised particles on a magnetic surface, CD-Rs and CD-RWs store data as microscopic reflective and nonreflective spots along the grooves. A drive reads the disc by shining a laser onto its surface and noting how the light reflects (or doesn't) off these spots in the grooves.

Mass-produced audio CDs and CD-ROMs are stamped by small presses that create tiny bumps (called lands) and holes (known as pits) in the grooves. Pits reflect light differently than lands along a disc's aluminium or gold surface, and the laser tells the difference by measuring the brightness of the reflection. CD-Rs and CD-RWs contain light-sensitive dyes or chemicals embedded beneath layers of protective plastic. When the high-intensity recording laser hits these light-sensitive materials, they become reflective (or not).

What exactly does "24x10x40" mean? These three numbers refer to the recording, rewriting and read speeds respectively. So, if a device has the specifications "24x10x40", it would record a write-once CD at 24-speed, record to rewritable CDs at 10-speed, and read CDs at 40-speed. If this doesn't mean much to you, it may help to think of these figures in terms of playing an audio CD. Playing a CD is the same thing as "reading it at 1-speed". For a standard CD that is filled to capacity, this will take 74 minutes. Therefore, reading a CD at 40-speed will take one-fortieth of that time, which is roughly two minutes.

These speeds are usually calculated as an average, so be prepared to accept a little lower performance than claimed in the specifications, particularly when it comes to read speeds. At the time of writing, 40x write burners are the fastest available, with 12x to 24x recording being pretty standard.

These acronyms are often used loosely, and sometimes interchangeably, for the drive and the media used by the drive. A CDR or CD-R refers to a recordable CD disk, or a CD drive that can write to blank CD disk. A CDRW or CD-RW refers to a rewritable CD disk, or a drive that supports recording to rewritable disks. All CDRW drives will write to CDR media. Not all CDR drives will write to CDRW media, although this is not so much a problem as it is virtually impossible to buy a plain CDR-only drive these days! Generally speaking, the term "CD" is used as a blanket term for both CDR and CDRW disks. Some CD media can store 700MB of data or 80 minutes of audio, although 650MB and 74 minutes is the standard.

A DVD (or DVD-ROM) drive will read all CD, CDR and CDRW disks as well as DVD disks such as those used for DVD video. While DVD almost always refers to video disks, DVD media can be used for other data, as if they were high capacity CDs. These writable DVD disks are called DVD-R. A DVDR drive is a DVD writer which will read and write to CD media as well as DVDR disks. A DVDRW is the rewritable version of DVDR. DVDs can contain up to 4.7GB of data, which is almost seven times the capacity of a CD.

Internal vs External

In the majority of cases, you'd be looking at purchasing an internal drive. These will always be cheaper and do not require any extra desk space. Bear in mind that they will require installation, although this is a simple procedure, even if you have never delved inside your PC's casing before! Buying an internal drive also gives you the option to convert it to an external drive should the need arise- a luxury you don't get with a specialised external drive.

All this aside, there are quite a few advantages to external drives, so the extra cost might be worth it to you. Firstly, an external drive is portable. It also enables you to write CDs from any PC, so if you are printing or working on one, you can burn on another. Additionally, a removable drive will usually connect via USB or FireWire port, so it won't use up an IDE connection in your PC. This means that you won't be restricted to the four drive connections that are standard on most motherboards.

On the downside, you need extra desk space for the box, and all your PCs will need compatible connectors- be it USB, USB2, FireWire etc. If you're not sure about getting an external drive, there is always the option to buy an external case sometime down the track. This will let you use an internal writer as an external writer- and possibly free up an IDE connector, as many external units available will convert the IDE interface on the drive to FireWire or USB

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