Thread: Construction and Operation of the Hard Disk Drive

To many people, a hard disk is a sealed black box of sorts-it is thought of as just a small device that somehow stores data. There is nothing wrong with this approach of course, as long as all you care about is that it stores data. If you use your hard disk as more than just a place to data and information, then you want to know more about your hard disk. It is hard to really understand the factors that affect performance, reliability and interfacing without knowing how the drive works internally. Fortunately, most hard disks are basically the same on the inside. While the technology evolves, many of the basics are unchanged from the first PC hard disks in the early 1980s.

A hard disk uses round, flat disks called platters, coated on both sides with a special media material designed to store information in the form of magnetic patterns. The platters are mounted by cutting a hole in the center and stacking them onto a spindle. The platters rotate at high speed, driven by a special spindle motor connected to the spindle. Special electromagnetic read/write devices called heads• are mounted onto sliders and used to either record information onto the disk or read information from it. The sliders are mounted onto arms, all of which are mechanically CGnnected into a single assembly and positioned ove'r the surface of the disk by a device called an actuator. A logic board controls the activity of the other components and communicates with the rest of the Pc.



Each surface of each platter on the disk can hold tens of billions of individual bits of data. These are organized into larger "chunks" for convenience, and to allow for easier and faster access to information. Each platter has two heads, one on the top of the platter and one on the bottom, so a hard disk with three platters (normally) has six surfaces and six total heads. Each platter has its information recorded in concentric circles called tracks. Each track is further broken down into smaller pieces called sectors, each of which holds 512 bytes of information.

The entire hard disk must be manufactured to a high degree of precision due to importance of the hard disk's role in the Pc. The main part of the disk is isolated from outside air to ensure that no contaminants ge~ onto the platters, which could cause damage to the read/write heads.