CD-Rom drives these days are as fast as Porsches, but is there any advantage when your processor is more of a Reliant Robin? By Steve Homer
It is virtually impossible to buy a PC without a CD-Rom drive these days. What was once a rare plaything has become a business necessity and an entertainment must. If you don't have one or feel your old one is getting out of date, which one should you buy?

CD-Roms first went on sale in the late Eighties, they were regarded with a certain amount of awe - a disc that could store a whole 650 megabytes! The trouble was that nobody could find anything to do with them. Slowly, a market developed, and today you can find everything from brilliant games to beautifully crafted reference works on CD-Rom.

The original CD-Rom drive was based on the audio CD, meaning the first generation of CD-Rom drives delivered data into the PC at 153 kilobytes a second. Eventually, some bright engineer realised that while you obviously could not play music faster than a fixed speed, reading data off a disc was something else altogether.

In 1993, the double-speed disc was born, delivering data twice as fast as the original drives. Slowly, they took the market over. Games loaded on to your hard disc twice as fast, and faster became better. After a couple of years, quad-speed CD-Rom drives came along and dominated the market in 1995. Today, the six-speed is set to take over from the quad as the dominant force, and a few eight-speeds are becoming available. But if you are thinking of buying a replacement CD-Rom drive, don't be blinded by speed.

"Everything in computing is about hitting the bottleneck," says Guy Sneesby, editor of CD-Rom magazine. "If you buy a really fast CD-Rom drive and have a slow processor, your game or interactive title will not run any faster than if you have a slower CD-Rom drive. If you want to copy applications onto your hard disc, you will be able to copy them faster, but if you are processing information, you may well find a faster drive makes no difference. You would do much better spending your money on more RAM or a processor upgrade."

Doug Murrie, business development manager for Pioneer, is also cautious about the benefit of raw speed - despite the fact that his company will launch the industry's first 10-speed CD-Rom drive in August. "You also have to look at access time. It is all very well being able to strip data off the disc very fast, but what most applications do is look around the disc, picking up different pieces of information. If you are searching articles in an encyclopaedia, the data can be read off the disc fast with a faster drive, but you will also be jumping around all over the disc, so the access time from place to place on the disc critically affects performance." Access time is a function of the design of the CD-Rom drive - how fast the pick-up can move to a different place on the disc and read it.

This is a big problem for the industry. While it is easy for consumers to understand the differences in speed, understanding access times - measured in milliseconds - is much harder. What is needed is a standard test for CD-Rom drives that accurately reflects the different ways they are used.

As a rule of thumb, there is only a marginal benefit going faster than quad speed at the moment. "Most software titles were written with quad speed in mind," says Ian Skelton, technical marketing manager at Creative Labs, one of the biggest manufacturers of CD-Rom drives.

He points out that the CD-Rom drive is idle for most of the time when an application is being used or a game is being played. Data is read from the drive into memory and then worked upon by the application. "It is only worth buying a really fast CD-Rom drive if you have a really fast Pentium PC," he said.

But if you have a really fast Pentium and want to get the fastest possible CD-Rom, should you wait for the 16-, 30- or 50-speed CD-Rom? Probably not.

Pioneer's 10-speed CD-Rom player rotates the disc at 4,000 RPM. This is remarkably fast for a non-enclosed disc. Hard-disc drives in PCs, which are in hermetically sealed units with smaller discs, usually spin at only 7,000 RPM. "The rate of change in CD-Rom speeds is going to slow down," says Doug Murrie of Pioneer. "We might see 12 or 14 or 16 but I doubt we will ever go above that. The physics just becomes too difficult if you spin the disc much faster."

In any case, CD-Rom drives as we know them are soon to be driven out of the market. At the end of this year, or more likely the middle of next year, DVD-Rom will come to market. This is a new technology that can store up to nine gigabytes on one side of the disc; discs can be two-sided, although they need to be flipped over to read the other side. DVD-Rom players will initially play data off these discs at around nine times old CD-Rom speeds and will also play CD-Rom at around that speed - the equivalent of a nine-speed.

When they go on sale, players will cost between pounds 300 and pounds 500. But the price will fall fast; the basic technology is very close to that used in CD-Rom drives.

For the moment, however, Ian Skelton sums up the best market advice. "The wave of low-priced quad-speed drives is a wonderful opportunity for people to have a look at CD-Rom. As most software on the market does not gain any real benefit from faster drives, there could not be a better time to buy a drive." A quad-speed drive can cost as little as pounds 50. A six-speed will probably set you back pounds 130 and eight-speed around pounds 150.

If you are looking to buy a CD-Rom drive, you would probably be best advised to buy a quad-speed now, upgrade to an eight-speed in a year's time (when they will probably only cost pounds 50) and then see at how the market has developed.