What is the data access method used to retrieve data by a hard disk?

Answer 1

The hard drive is truly a remarkable piece of engineering. It could be compared to a cross between a record player and a tape recorder.

Metal platters, coated with magnetic material, spin at up to 10,000 RPM's beneath magnetic heads. The heads actually "float" over the platter when the drive is running so as not to scrape the magnetic coating off.

The information is arranged on the hard drive in Tracks and Sectors. A track is one concentric circle, where a sector is a "pie slice".

When you save something to the hard drive, the computer looks at a special area of the drive called the FAT (File Allocation Table), and determines what sectors are currently available to save the data. The heads then are moved over the appropriate sectors, and the information is "Recorded" onto the spinning magnetic platter.

When you read something from the hard drive, the computer first looks at the FAT to see where it is saved, and then moves the heads to read the information spinning on the platters below it.

Since the hard drive is spinning so fast, care must be taken not to submit the drive to shocks or bumps. If you've ever played with a gyroscope, and seen how it reacts (kind of "wobbling" when it is bumped), the same thing can happen with a hard drive. However, that wobbling could cause the heads to make contact with the platters and scrape the magnetic coating. That can lead to the loss of data where it has been scraped off, or even worse, a head "crash", where that scraped material gets caught between the head and the platter, causing a LOT of damage and data loss.

* Note: I know that the simple track/sector analogy goes way back to MFM drives and so forth, but for the sake of simplicity, I wasn't going to get into heavy technical details about interleaving, flexible sectors per track, RLL, IDE, etc. etc. Without going into a crazy level of details, this explanation is valid.

Answer 2

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