All About...

Hard Drives

I n the early days of personal computing, pm grams and files required little storage space.

They were easily stored on 360 kilobyte (KB) and 1.2 megabyte (MB) 5.25-inch diskettes or 720KB and 1.44MB 3.5-inch diskettes. But as computing technology progressed, so did the need for storage. Hard drives entered the picture in 1982, g~vmg users a whopping 5MB of storage upon which to store files. As increasingly complex programs gobbled up more storage space, the average PC hard drive has grown to more than 2 gigabytes (GB), more than 400 times the size of the first hard drives.

As a result of this technological development, the hard drive has become one of the most important computer components. It provides the prim~uy storage space for the computer's operating system and all your programs and data files. Like the motherboard and random-access memory (RAM), a failed hard drive can render a computer useless. But unlike a motherboard and RAM, the hard drive is a mechanical device with moving parts, making it more suscepfible to damage. So knowing how a hard drive works will help you maintain it properly, gi~ng you trouble-free computing.

Most hard drives are permanently connected inside your computer. Others, however, are removable hard drives that can be safely secured or easily transferred to more than one computer without leaving copies of sensitive files behind for prying eyes Portable computers also have removable internal hard drives designed for easy replacement and for security.

Hi Hard Drive Geography. A hard drive has five main components: platters, spindle, read/write heads, head actuator, and a circuit board.

Platters, also called disks, are the part of the hard drive where data is stored. They are rigid magnetic disks made of an aluminum alloy covered with a thin layer of iron oxide. When a computer is on, these platters constantly spin on a spindle, which is driven by a motor. Each side of every platter has a readlwrite head, which writes data to and reads data from each

platter. They are attached to the head actuator, which precisely moves the read-write heads across the platters. An integrated circuit board, also called a logic board, allows the computer to move the read/write heads across the platter surfaces.

Hard drives operate much like a record player spinning a vinyl record. Just like a record player's arm that holds the needle, the hard drive has a movable arm that carries the read/write heads across the platter's magnetic surface. Instead of grooves etched into the record's vinyl surface, magnetic sectors formed by formatting the disk are placed in concentric patterns on the platter.

Picture several vinyl records (platters) stacked on top of each other with just enough room for the needle (read/write head) and arm (head actuator) to move back and forth. ?hen picture the entire device sealed inside a case. That's how a hard drive is designed.

On a vinyl record, the needle is able to translate the etchings in the grooves that were made by electrical impulses when the recording was made. The needle sends these sounds to the audio circuih·y, which translates the electrical impulses into sound waves that come from the record player's speaker system.

Computers record and "play back" data on hard drives much like a record player. Data is translated into a slies of bits. The hard drive receives these bits and uses the read/write heads to magnetically store or write the bits on one of the platters. This process involves converting the data to positive and negative magnetic fields on the platter's surface. The computer keeps track of where these bits are stored on the various platters so when you want to retrieve them, it can direct the read/write heads to the precise locations on the platters where the data is stored. The heads recognize the data stored as magnetic fields and send it to the computer's monitor within a few millionths of a second.

Although the storage area of a platter's surface is smooth and unbroken, formatting the hard drive (preparing it so it can store data) gives it textured features. The surface's magnetic coating is divided into a series of cylinders containing tracks; each track is divided into sectors. These hard drive divisions are like a map that lets a computer determine exactly where it stores data.

A cylinder is a set of tracks on a platter that can be accessed without read/write head movement. Formatting a hard drive lays down an exact pattern of tracks that are the same distance from the spindle around which the platters rotate. Each group of tracks forms the shape of a cylinder.

A track is the part of the platter's surface that passes under one read/write head while it is stationary. Tracks form concentric circles beginning with track O at the outer edge of the disk. How close together these tracks are placed on a platter determines the amount of data it can hold.

Each track is divided into sectors, which are identified by the side of the disk on which they are located, their track number, and the sector number within the track.

Computers use a file system to organize the files on a disk. Each operating system-Macintosh, DOS, Windows, Windows Y5, OS/2, and Wmdows ~i~--can only work with one or two filing systems. This is one reason why data saved to a disk formatted for one system cannot be read by another system. The File Allocation Table (FAT) is the file system developed by Microsoft Corp. for DOS and Windows. The common file systems are FAT (used by DOS, Wmdows 3.1, and early versions