A Study On Hard Disk Drive Computer Science Essay


Every desktop computer, laptop and netbook contains a hard-disk drive. The hard-disk drive, better known as the hard drive, is one of the most vital components in a computer. The hard drive stores information for the computer in a non-volatile way, meaning that when the user shuts off the computer, all the information he saved will still be there when he turns the computer back on. Today, hard drives can store an enormous amount of information. We will take a look at how a hard drive operates and saves information. Figure 1 is a picture of a typical hard drive (Hallock).

Figure 1: Enclosed hard drive (Hallock)

Six basic elements make up the composition of a hard drive: The enclosure, spindle motor, hard drive platters, actuator arm, interface and logic board. The enclosure is simply the outer shell that protects and holds everything together. The four largest and most important properties that will be outlined below are the interface, logic board, hard drive platters, spindle motor, and the read/write to disk. The actuator arm will be referred to and described within these outlined sections (Hallock).


A hard drive connects to your computer through a specific type of interface (Bleeping Computer). The hard drive port and the port on the computer where they connect must be the same; otherwise they will not be able to sync up together.

Logic Board

The logic board performs several significant operations. The logic board is the "brain" of the hard drive. It tells the computer what the drive is, how big it is, what cable its connected to, and how to access the drive in your operating system. Figure 2 below is a picture of a logic board (Hallock).

Another key function of the logic board is the read/write cache process, without this the hard drive would be slow in saving and retrieving files. When a computer is told to open 1,000 megabytes of information, the hard drive passes the information to you as quickly as it is able through the cache process. While the hard drive is loading the first 16MB of the file, the next chunk of data is prepared to roll and is waiting in the cache; when you open the cached chunk of data, another is fed into the cache, and so on until all the information is opened. This is the read portion of the cache process, the reverse of this process occurs to write information (Hallock). This cache process is an integral part of the read/write to disk function that is described in a section below.

Hard Drive Platters

Platters are the round plates in the Figure 4 below (Bleeping Computer). Platters contain all the information stored on the hard drive. The platters themselves are the most important and complicated component included in a hard drive. Today's platters are thin disks (thus the "hard disk" name) of glass or aluminum, coated with an ultra-thin layer of a cobalt alloy, which is naturally magnetic. Data is written to sectors which are organized into concentric rings outwards from the spindle called tracks, and all of those are managed into clusters by the file system you've chosen. To write the data, the actuator arm aligns the magnetization of the platter in a pattern recognizable to the hard drive's logic board (Hallock). In other words, the actuator arm swings across the platter to find information that the user desires.

The Spindle Motor

The spindle motor is the most basic moving component in a hard drive. The spindle motor is controlled by the logic board and is responsible for turning the hard disk platters, allowing the hard drive to operate. The faster the spindle spins the faster the read/write capabilities the hard drive has. Below in Figure 3 is a spindle motor stripped of its platters and all other components (PC Guide).

Figure 3: Spindle Motor (PC Guide)

Read/Write to Disk

The read process is when the user requests data from the hard drive and it is transmitted to the computer. The write process is when the user saves information on the hard drive for later use. Here are the steps in the read/write process:

  • The user requests information on the hard drive.

  • The operating system accesses the files and locations via the motherboard's hard drive controller.

  • The operating system tells the hard drive's logic board that it wants a file.

  • The logic board spins up the platters on the spindle.

  • The actuator arm is moved into position.

  • The logic board reads and amplifies the very weak, isolated magnetic fields that comprise your data.

  • The logic board begins using the actuator to read information from the sectors in the requested cluster.

  • Information is streamed into the hard drive cache.

  • The information is fed from the cache, to the hard drive controller, to you and RAM.
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The write process is almost the exact opposite, except instead of accessing the platters to find a file's location; it's accessing the file table to find free clusters for write space (Hallock).


Hard drives are the main component in many computer-driven technologies today. There are seven basic parts to a hard drive; the enclosure, spindle, platter, motor, actuator arm, interface and logic board. A hard drive in where all the information is stored on a computer. Hard drives have been a key innovative technology in saving and storing data that has become such an integral part of our society.

Works Cited

Hallock, Robert. "How Hard Drives Work."Icrontic. N.p., 5 June 2007. Web.

         10 Mar. 2010.

"Hard Disk Spindle Motor."The PC Guide. N.p., 17 April 2001. Web.

         12 Mar. 2010.

"How Hard Drives Work."Bleeping Computer. Bleeping Computer ,

         12 Nov. 2005. Web. 10 Mar., 2010.