Hard Disks for Web Servers

Jimmy Martin

A web server needs somewhere to store all of its web pages, programs, databases, images and any other file that the webmaster needs. This mass storage device must have large capacity, excellent reliability and be as fast as possible. There is only one contender for this role: the hard disk drive.

As you can tell from the name, a hard disk contains one or more solid metal disks, called platters. These spin around at high speed: 7,200 revolutions per minute in a standard drive, but up to 15,000 rpm in the most advanced drives. They are coated with tiny magnetic particles. Just as a magnet has North and South poles, these particles can be magnetized in two directions. I'm sure you know that computers work with strings of ones and zeros. Well, in a hard disk drive, these ones and zeros are recorded as tiny areas of North and South on the hard disk platters.

To read and write data onto the platters, the hard disk drive has little devices called 'heads'. These are able to swing from side to side across the platters just like the stylus of a record player. The heads are able to detect the direction of the magnetism recorded on the platter so they can read data, and they are also able to magnetize the platters to write data. Amazingly, they ride on a cushion of air, less than a millionth of an inch above the spinning platters! A particle of dust is enormous by comparison, and if the heads hit a dust particle they would crash into the platter and the drive would fail. There is a special air filter in the drive to stop any dust entering.

A hard disk drive will usually have more than one platter to store data on, and it will have a read/write head for each side of each platter (data can be stored on both sides). This increases the amount of data stored in the drive. Modern drives have up to 4 platters and 8 heads.

Next we will look at some of the vocabulary of hard disk drives.