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Speaker 1: Welcome to brain Stuff from how stuff works dot com

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Speaker 1: where smart happens. Join Josh and Chuck, the guys who

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Speaker 1: bring you stuff you should know, as they take a

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Speaker 1: trip around the world to help you get smarter in

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Speaker 1: a topsy turv economy. Check out the all new super

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Speaker 1: Stuff Guide to the Economy from how stuff Works dot Com,

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Speaker 1: available now exclusively on iTunes. I am Marshall Brain with

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Speaker 1: today's question, what is the churning sound I hear from

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Speaker 1: my hard drive whenever it's retrieving data. Let's say you

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Speaker 1: do something simple like you double click on the icon

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Speaker 1: for a spreadsheet file. This simple act on many computers

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Speaker 1: can take ten or twenty seconds to complete, and all

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Speaker 1: during that time, the hard disc is churning away. The

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Speaker 1: hard disc access light flickers, and the drive might make

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Speaker 1: a horroring rumbling or high pitched whinding noise. If the

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Speaker 1: mechanism in the drive is loud, you definitely know that

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Speaker 1: something is going on inside the drive. There's an arm

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Speaker 1: that holds the read write heads. This arm can move

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Speaker 1: the heads two tracks near the hub or near the

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Speaker 1: edge of the disk. A normal hard disc is five

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Speaker 1: inches or less than diameter, so this arm can move

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Speaker 1: about two inches across the face of the disk. The

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Speaker 1: speed at which this arm can move is astonishing. The

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Speaker 1: arm is very light and its actuator is powerful and precise.

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Speaker 1: The arm can slide across the face of the disc

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Speaker 1: hundreds of times per second if it needs to. If

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Speaker 1: you think about how a speaker works, this isn't much different.

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Speaker 1: A speaker is moving a lightweight cone back and forth

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Speaker 1: hundreds of times per second to generate sound. As the

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Speaker 1: hard disc arm moves back and forth rapidly, it sets

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Speaker 1: up vibrations that our ears here as sounds. Why when

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Speaker 1: you click on a simple spreadsheet file would the disks

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Speaker 1: heads have to move so much ten or twenty seconds

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Speaker 1: worth of movement. Sometimes there are two things that cause

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Speaker 1: all the movement. First, to start a spreadsheet application like Excel,

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Speaker 1: the hard disc cast to load the application itself, along

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Speaker 1: with a number of libraries that support the application. The

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Speaker 1: total size of all these different files might be many megabytes,

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Speaker 1: and the files are scattered all over the disk. Loading

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Speaker 1: twenty or thirty megabytes of data takes time and requires

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Speaker 1: the disc head to move thousands of times to retrieve

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Speaker 1: all the pieces. The data file itself has to load also,

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Speaker 1: and that's the second thing. The operating system has to

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Speaker 1: move the head to the drive's directory to find the folder,

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Speaker 1: make sure that the file name exists, and then discover

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Speaker 1: the location of the file. Then the operating system needs

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Speaker 1: to read dozens of tracks scattered all over the drive

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Speaker 1: to access to the file altogether. Clicking on a single

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Speaker 1: icon may cause the disc heads to reposition themselves thousands

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Speaker 1: of times in the process. This is why you hear

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Speaker 1: the drive churning. It's doing a lot of work. Do

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Speaker 1: you have any ideas or suggestions for this podcast? If so,

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Speaker 1: please send me an email at podcast at how stuff

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Speaker 1: works dot com. For more on this and thousands of

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Speaker 1: other topics, go to how stuff works dot com. M