Welcome to brain Stuff from how stuff works dot com where smart happens. Join Josh and Chuck, the guys who bring you stuff you should know, as they take a trip around the world to help you get smarter in a topsy turv economy. Check out the all new super Stuff Guide to the Economy from how stuff Works dot Com, available now exclusively on iTunes. I am Marshall Brain with today's question, what is the churning sound I hear from
my hard drive whenever it's retrieving data. Let's say you do something simple like you double click on the icon for a spreadsheet file. This simple act on many computers can take ten or twenty seconds to complete, and all during that time, the hard disc is churning away. The hard disc access light flickers, and the drive might make a horroring rumbling or high pitched whinding noise. If the mechanism in the drive is loud, you definitely know that
something is going on inside the drive. There's an arm that holds the read write heads. This arm can move the heads two tracks near the hub or near the edge of the disk. A normal hard disc is five inches or less than diameter, so this arm can move about two inches across the face of the disk. The speed at which this arm can move is astonishing. The arm is very light and its actuator is powerful and precise. The arm can slide across the face of the disc
hundreds of times per second if it needs to. If you think about how a speaker works, this isn't much different. A speaker is moving a lightweight cone back and forth hundreds of times per second to generate sound. As the hard disc arm moves back and forth rapidly, it sets up vibrations that our ears here as sounds. Why when you click on a simple spreadsheet file would the disks heads have to move so much ten or twenty seconds worth of movement. Sometimes there are two things that cause
all the movement. First, to start a spreadsheet application like Excel, the hard disc cast to load the application itself, along with a number of libraries that support the application. The total size of all these different files might be many megabytes, and the files are scattered all over the disk. Loading twenty or thirty megabytes of data takes time and requires the disc head to move thousands of times to retrieve all the pieces. The data file itself has to load also,
and that's the second thing. The operating system has to move the head to the drive's directory to find the folder, make sure that the file name exists, and then discover the location of the file. Then the operating system needs to read dozens of tracks scattered all over the drive to access to the file altogether. Clicking on a single icon may cause the disc heads to reposition themselves thousands of times in the process. This is why you hear the drive churning. It's doing a lot of work. Do
you have any ideas or suggestions for this podcast? If so, please send me an email at podcast at how stuff works dot com. For more on this and thousands of other topics, go to how stuff works dot com. M