Parts of a Hard Drive Component

A hard drive stores data on metal discs.

The hard drive is responsible for most of the storage needs of the computer. Entry-level hard drives store hundreds of gigabytes of data, and the largest hard drives store thousands. Though computer hard drives have made one quantum leap after another over the years in terms of storage capacity, the basic design of the hard drive has changed less than one might think. Though hard drives operate in much the same fashion as they did in the 1980s, they are faster, larger and more reliable than ever before.

Metal Platters

The data in a hard drive is stored on one or more rigid metal platters, similar in shape to a compact disc. The platters are coated with a thin medium that responds to magnetic impulses. When a particle is oriented in one direction, it represents a zero, and in the other direction, a one. The technology is similar to that used for diskettes or audio cassettes, but on a much finer scale due to the vast amount of data.

Head and Actuator

The read/write head in a hard drive is responsible for changing the alignment of the magnetic particles on the surface of the platters when you want to write data, or detecting the existing alignment of particles to read data. The actuator changes the position of the read/write head when needed. The read/write head is similar in appearance to the stylus of a record player. The head remains so close to the platters as they spin that a speck of dust would be large enough to send the head colliding off of its path. Hard drives are assembled in dust-free clean rooms for this reason.

Motor

The hard drive motor is responsible for spinning the platters at breakneck speeds. In a typical desktop hard drive, the motor spins at 7,200 revolutions per minute (RPM). The fastest hard drive motors spin at 15,000 RPM, while the tiny hard drive in an iPod spins at 4,200 RPM. Because the motor is the hardest-working part of a hard drive, mechanically speaking, it is often the cause of hard drive failure.

Printed Circuit Board (PCB)

The hard drive printed circuit board (PCB) contains the computer circuitry needed to control the drive. The functions of the PCB include locating data on the physical platters when you need to read a file, and finding free space when you need to write data. Additionally, the components on the PCB are responsible for interpreting the alignment of the particles on the platters and converting it to data that your computer understands.

Cache

The hard drive cache is a memory chip on the PCB. The cache serves as a buffer when you write data on the drive. When you send data to the hard drive, it goes to the cache before being committed to the platters. When the data is stored in the cache, the hard drive reports to the operating system that the write operation is complete, then moves the data to the platters. This system of writing data makes the computer feel faster. Because the cache is faster than the platters, the write operation appears to finish instantly, though in fact additional fractions of a second may pass before the data moves from the cache to the platters.

Data and Power Connectors

The data and power connectors are on the back of the hard drive. The data connector connects to the motherboard of the computer, and the power connector connects to the power supply. In laptop computers, these connectors are generally combined. The data connector sends information between the hard drive and the rest of the computer.

References

• PCGuide: Construction and Operation of the Hard Disk
• The Linux System Administrator's Guide: Hard Disks
• Dux Computer Digest: How a Hard Disk Drive Works