The article How Binary Numbers are Used to Store Data describes how numbers, text, and graphics are stored using either a "1" or a "0". This article describes how each "1" or "0" may be written to or read from a Hard Disk Drive (HDD).
Hard Disk Drive Data Storage - Why Use Magnetics?
Every magnet has a "North" and "South" pole, and there is no stable state in between. This means that magnets are well suited to be used to store binary numbers, with a "North" representing a "0", and a "South" representing a "1". Hard disk drives use this method to store data. Magnetic storage is very stable compared with other methods, because magnets, once set, will stay in the orientation in which they are set, unless something makes them change.
Hard Disk Drive Data Storage - Writing to a Disk Drive
The basic principle used to write one bit (short for "binary digit") on to the surface of a disk drive is Faraday's Law of Induction. Figure 2 shows a basic electromagnet. When a voltage is applied from a battery to the wire wrapped around a nail, the iron nail becomes magnetized. The tip of the magnet becomes a "North" pole whereas the head of the nail becomes a "South" pole. The tip of the magnet then magnetizes one bit on the surface of the disk. If the contacts on the battery are switched, the tip of the nail becomes a "South" pole and the head becomes a "North".
For example, the ASCII code for the letter "A" is 65 in decimal, or 01000001 in binary. The sequence of magnets needed to store the letter "A" is therefore NSNNNNNS.
Hard Disk Drive Data Storage - Reading from a Disk Drive
Reading from the disk drive uses a different principle than writing to it. To read a particular bit, a detector is put over the top of the bit to be read. The detector uses a property called magnetoresistance to work. Certain materials, in the presence of a magnetic field, will change resistance slightly. The resistance of the detector is measured, and a change in resistance indicates a change in polarity of the bit (magnet) below the detector.
Hard Disk Drive Data Storage - Summary
Magnetic Disks encode data using the binary number system. At the most basic level, the various types of data - numerical, text, images and music - can all be represented using only the digits "0" and "1". These "bits" are arranged in groups of eight, called bytes. Disk Drives use magnetic materials to store data, and these work because they can only be in one of two states - "North" and "South". The basic use of binary numbers to store the data is the same as DVDs and CDs, as well as Solid State memory Devices.
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