Introduction

Nearly all personal computers require a method for storing large amounts of data quickly, efficiently, and safely. A device called the hard disk drive commonly provides this function. This device is based on the idea of storing binary data on magnetic platters, much like a floppy disk drive; however, the hard disk drive is a very different product. It contains multiple data platters, which allows for a much greater amount of storage. In addition, the hard disk drive performs more quickly than many other methods of storage.

Description

Externally, the drive is simply a metallic case, featured only with two interface connectors and typically, a jumper block. Internally, the drive contains a number of platters, separated by actuator arms and read/write heads. The read/write heads read information from the platters and transfer it out through the interface connector.

Major Parts

The hard drive consists of 8 major parts; the case, platters, actuator arm, read/write head, CPU (Central Processing Unit), interface connector, power connector and jumper block (fig 1).

Fig 1; Overview of hard drive assembly

Source: Quantum storage

External Overview

On the outside, the hard disk drive appears to be little more than a solid metal case weighing slightly more than 1 pound (1.2lbs). Typically, a drive measures 5 ½” long, 4” wide, and 1” deep and contains very few notable features, none of which are moveable.

The backside of a drive features an I/O (Input/Output) interface for connecting with a computer, a jumper block for configuring the drive, and a power connector (fig 2).

fig 2; Rear view of a hard disk drive

Case

The case is constructed of solid aluminum and it is used to shield the sensitive internal components from the outside air. The case is airtight and provides no obvious point of entry. A good portion of the weight of the drive is in the case.

Interface Connector

The interface connector is a standardized connector providing a method for interacting with the internal components of the hard drive. It size, depending on the interface standard (IDE, SCSI, MFM), varies between 3” and 3 ½” wide and ¼” tall.

Power Connector

The power connector provides power to the electronic components inside the hard disk drive. Four wires provide current. The connector is 1” x ¼” in size.

Jumper Block

The jumper block is an array of short metal pins. Two consecutive pins (in the horizontal or vertical direction) may be shorted out by placing a small plastic sleeve on top of them. The sleeve contains a metallic bridge made of an electrically conductive material.

Internal Overview

Internally, the drive is much more complex. There are a number of circular platters stacked atop one another. These platters provide storage for all the data in the system. In-between each of the platters is an actuator arm. At the tip of the actuator arm is a read/write head (fig 3)

fig 3; Internal view of a hard disk drive

Platter

The platters are 3” in diameter and constructed of a rigid aluminum alloy, giving them a silver color. Although wide, the platters are extremely thin, less than 1/10” thick. The platters are coated with a film of magnetic particles, which are able to maintain their state of magnetic polarity. The platters spin around the center at a rate up to 10,000-RPM (rotations per minute).

Actuator Arms

The actuator arms are positioned in-between each pair of platters. They are slightly longer than the radius of the platter (1 ½”). The actuator arms are able to position themselves at any point, moving linearly from the center of the platter to the outer edge of the drive. At each the ends of each arm are two Read/Write heads.

Read/Write head

The read/write heads are microscopic electrical devices at the end of each actuator arm. The read/write heads detect the polarity of the magnetic particles on the platters. There is a read/write head on the top and the bottom of each actuator arm and the corresponding read/write head handles the nearest platter. As the platters rotate past the read/write heads, the pattern of polarities are converted into an electrical signal which is transmitted to the CPU.

CPU

The CPU for the hard disk drive controls the positioning of the actuator arms, the spinning of the magnetic platters, and the interface to the computer via the interface connector. The CPU receives requests for services from the computer through the interface connector. Next it translates the commands into a series of operations performed upon the internal assembly. If the service was a request for data, the CPU translates the electrical signals returned by the read/write heads into a format, which may be transmitted back through the interface connector.

Summary

The hard disk drive is a very complex interdependent electronic component. If any one of the hard disk drive’s components fail, the device would be completely unable to perform its job. Together, these components provide a robust method for storing vast amounts of data—Speedily, securely, and most important of all, in a way that is transparent to the user.