Computer Basics, Part 2: The Hard Drive

The hard drive is a highly sensitive and complicated device that most of us tend to take for granted. Just what it is and -- how it works -- is the subject of this second article on computer hardware [read part 1 here].

If you were to remove the sealed cover on the drive, what you would see is a number of platters attached to a fairly thick shaft that contains a type of motor known as a servo motor. The servo motor has the characteristic of being easily controlled and stable when considering the speed of rotation. The platters are spun by the motor at a rate of speed designated by the manufacturer.

Click here to see the inside of a hard drive.

The platters themselves are actually metal disks that are highly polished and coated with a compound that is actually finely ground iron. The fineness of the compound determines the amount of data that can be stored on the surface of the platter.

You will also see an arm that extends across the surface of the platter. In fact, the arm is actually doubled because there is an arm for each of the two sides of each platter. On the end of those arm is a 'head' that is similar to the record and playback heads in a tape recorder.

When in operation, the head on the end of the arm actually 'flies' due to something called 'ground effect'. The head moves less than a thousandth of an inch above the surface. In fact, the head is so close that a fingerprint on the platter -- or even a particle of smoke -- would touch the head, causing it to 'crash' into the surface of the platter.

The drives are put together in a 'clean room' at the manufacturer to prevent the contamination of dirt, dust, and hair. The people that work in such places wear hooded coveralls, face masks, and gloves to keep the drive interior clean.

Before we go further, there are a few things we need to discuss. One of those is the data that is recorded on the platters. Just like the tape cassette used in tape recorders, the information is recorded on the coated platters. But before the platter can be used, it needs to be 'partitioned' and 'formatted'.

You can think of partitioning a drive synonymous to plotting out a town by setting the boundaries and dividing it up into neighborhoods. Partitioning determines the type of use a section of the drive will be used for, whether it be for 'swap' space or data.

Once the drive has been partitioned, it must be formatted. Think of it as drawing in of the streets in a town. With the streets in place each lot on the streets is given a number. 327 Sunshine Street is a specific location in a town that tells you where you live, where to send mail, and routes the various services.

Another thing is that a hard drive, in fact any drive, is a 'binary' device in that the addressing method used is based on the binary numbering system. The reason for this is because the computer operates in binary. We'll go into this in detail in a later article.

The term that applies to the result of the format is 'sectoring'. Each sector contains spaces for 512 bytes or characters, each character consisting of 8 bits. It gets stranger!

Using our previous example, each sector is like a street block in our little town. Each block has a group of addresses for the lots on it. So does the sector, except the sector actually has 512 places for data to be recorded. There is yet another form of describing the drive and that is the 'cluster'. All the cluster defines is the specific group of sectors the operating system can efficiently use.

If you haven't encountered this stuff before, your head would be spinning. But don't worry, the GOOD thing about all this is the computer knows how to deal with it so you don't have to! ;-)