Physical aspects of the hard disk
First, let us look at the construction of the hard disk.
Read/write heads
All hard disks consist of thin platters with a magnetic coating. They rotate quite fast inside a metal container. Their design causes them to ride on a microscopic cushion of air, without touching the platter.
Data are written and read by read/write heads. They register bits from the magnetic coating, which races
past them. On the illustration below, you see a hard disk with three platters. It has 6 read/write heads, which move synchronously. The arms, which guide the movement of the read/write heads, move in and out almost like the pick-up arm
in an old fashioned phonograph. As illustrated below, there will typically be 6 arms, each with read/write
heads. The synchronous movement of the these arms is performed by an electro-mechanical system
called head actuator. The hard disk data can only be attained via one head at a time.
The read/write head consists of a tiny electromagnet. The shape of the head end acts like an air foil, lifting the read/write read slightly above the spinning disk below.
When the disk rotates under the read/write head, it can either read existing data or write new ones: If a current is applied to the coil, the head will become magnetic. This magnetism will orient the micro
magnets in the track. This is write mode. If the head moves along the track without current applied to the coil, it will sense the micro magnets in the track. This magnetism will induce a current in the coil. These flashes of current represent the
data on the disk. This is read mode. he read/write heads are by far the most expensive parts of the hard disk. They are incredibly tiny. In modern hard disks they float between 5 and 1 micro inches (millionths of an inch) above the disk. When the PC is shut down, they are auto parked on a designated area of the disk, so they will not be damaged during transport.
First, let us look at the construction of the hard disk.
Read/write heads
All hard disks consist of thin platters with a magnetic coating. They rotate quite fast inside a metal container. Their design causes them to ride on a microscopic cushion of air, without touching the platter.
Data are written and read by read/write heads. They register bits from the magnetic coating, which races
past them. On the illustration below, you see a hard disk with three platters. It has 6 read/write heads, which move synchronously. The arms, which guide the movement of the read/write heads, move in and out almost like the pick-up arm
in an old fashioned phonograph. As illustrated below, there will typically be 6 arms, each with read/write
heads. The synchronous movement of the these arms is performed by an electro-mechanical system
called head actuator. The hard disk data can only be attained via one head at a time.
The read/write head consists of a tiny electromagnet. The shape of the head end acts like an air foil, lifting the read/write read slightly above the spinning disk below.
When the disk rotates under the read/write head, it can either read existing data or write new ones: If a current is applied to the coil, the head will become magnetic. This magnetism will orient the micro
magnets in the track. This is write mode. If the head moves along the track without current applied to the coil, it will sense the micro magnets in the track. This magnetism will induce a current in the coil. These flashes of current represent the
data on the disk. This is read mode. he read/write heads are by far the most expensive parts of the hard disk. They are incredibly tiny. In modern hard disks they float between 5 and 1 micro inches (millionths of an inch) above the disk. When the PC is shut down, they are auto parked on a designated area of the disk, so they will not be damaged during transport.
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