November 2002 COMPUTER Help's Q&A The Internet

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November 2002 How Hard Disks Work

Nearly every desktop computer and server in use today contains one or more hard disk drives.

These hard disks do one thing well -- they store changing digital information in a relatively permanent form. They give computers the ability to remember things when the power goes out.

Hard Disk Basics

Hard disks were invented in the 1950s. They started as large disks up to 20 inches in diameter holding just a few megabytes.

They were originally called "fixed disks" or "Winchesters" (a code name used for a popular IBM product). They later became known as "hard disks" to distinguish them from "floppy disks".

Hard disks have a hard platter that holds the magnetic medium, as opposed to the flexible plastic film found in tapes and floppies.

A typical desktop machine will have a hard disk with a capacity of between 10 and 40 gigabytes. Data is stored onto the disk in the form of files.

A file is simply a named collection of bytes. The bytes might be the ASCII codes for the characters of a text file, or they could be the instructions of a software application for the computer to execute, or they could be the records of a database, or they could be the pixel colors for a GIF image.

No matter what it contains, however, a file is simply a string of bytes.

When a program running on the computer requests a file, the hard disk retrieves its bytes and sends them to the CPU one at a time.

There are two ways to measure the performance of a hard disk:

Data Rate

The data rate is the number of bytes per second that the drive can deliver to the CPU. Rates between 5 and 40 megabytes per second are common.

Seek Time

The seek time is the amount of time between when the CPU requests a file and when the first byte of the file is sent to the CPU. Times between 10 and 20 milliseconds are common.

The other important parameter is the capacity of the drive, which is the number of bytes it can hold.

Typically we now see terms like 30 Gig or 40 Gig Hard Drives. (Short for Gigabytes)

Data storage is measured in (KB) kilobytes (1,024 bytes), (Meg) megabytes (1,024 kilobytes), (Gig) gigabytes (1,024 megabytes), and terabytes (1,024 gigabytes). Data storage is not to be confused with "memory", which refers to temporary storage areas within a computer.

Data is stored on the surface of a platter in sectors and tracks. Tracks are concentric circles, and sectors are pie-shaped wedges on a track.

A sector contains a fixed number of bytes -- for example, 256 or 512.

Either at the drive or the operating system level, sectors are often grouped together into clusters.

Partition Size (4. 8, 16 or 32 KB) determines cluster size.

What does all this mean to you?

To be as efficient as possible with your data storage you should understand cluster size. You might have a file that is 1 KB in size.

So with a cluster size of 32 KB then that file actually occupies 32 KB not 1 KB.

Therefore, a large number of small files like Temporary Internet Files that typically take up less than 1 KB per file occupy more of your Hard Drive than you realize. In future columns we may discuss how to maximize your Hard Drive usage.

Thanks to Marshall Brian's How Stuff Works Web Site at: www.howstuffworks.com/ for most of this article.

Read more about Hard Drives in detail with pictures, visit www.pctechguide.com/04disks.htm

Send your Internet and E-mail questions to: Q&AComputerClub@comphelp2000.com

Dale Wiley :)

(#1 Rated MS Word Expert at www.Askme.com)