Hard disks, sometimes also called hard drives, are storage devices for the computer. Unlike the computer's memory, hard drives are not within the circuitry of the computer and are not on the motherboard itself. There is at least one hard disk within every single modern desktop computer! They are used to store large amounts of information. The data stored in a hard disk will not be erased when the computer is turned off, like the data stored in the computer's random-access memory (RAM). When the central processing unit of a computer needs to use information stored on the hard disk, the data will be copied from the hard disk to the computer's RAM. This is so a computer can permanently store large amounts of information and operate at fast speeds at the same time!
Modern hard disks can store anywhere between 10 and 40 gigabytes. One gigabyte is 1 billion bytes, and one byte is 8 bits. Bits are a single binary digit-a 1 or a 0. Eight of these bits combined equal one byte, and one byte is used to represent a single letter, number, punctuation mark, or another special character. Hard disks can be used to store any kind of information from text files to graphics to the instructions in a software application!
All hard disks pretty much have the same basic parts:
The head disk assembly is the aluminum case in which the hard drive is contained. It is a chamber that holds all of a hard disk's components. In the inside, you can find platters, a spindle motor, heads, and a head actuator, while on the outside there is a logic board.
Courtesy of The PC Tech Guide.
Copyright (c) Dave
Anderson.
Hard disk drives range in size, but are usually 5.25 inches or 3.5 inches. This size usually depends on the size of the platters in the disk.
Platters:
Platters are rigid disks where the information is actually stored. Most hard disk drives have at least two platters. The size of the platter determines how much information the hard disk can store. When the hard disk is operating, a platter can make up to 7,200 revolutions per minute.
Originally, platters were made out of an aluminum material, but now there are new platters that are made out of a mixture of glass and cement. Glass platters are thinner than aluminum ones, and they can also resist heat better.
Platters are all coated with a magnetic oxide material. This mixture is the reason why some platters may seem to have an orange-y color. These are the materials responsible for allowing the platters to record and store data.
Data is stored on the platters in a pattern of tracks and sectors. Tracks are concentric circles, like a bulls eye, while sectors are similar to pizza slices. Each sector contains a certain number of bytes.
Read/Write Heads:
The read/write heads are mechanisms that allow the hard disk to read and write information and data. There is one head on every side of a platter. The heads are rested on the platter when the disk is not in use, but when the hard disk is in use, the spinning of the platters cause the heads to lift slightly up, making them seem as if they are floating in the air. However, the heads lift up so little that even a particle of dust lying in the space they lift up would cause a problem!
Head Actuators:
Head actuators are devices to which the read/write heads are attached. They are responsible for moving the heads around on the platters to different tracks and sectors.
There are two different types of head actuators. First, there is the stepper motor actuator. There are stop positions on the read/write heads, and the stepper motor actuators have motors that move from one stop position to another. Unfortunately, it is very slow.
The second kind of head actuators is the servo motor actuators. These are found in almost all modern hard disks. They use a special form of the binary system to position the read/write head over the right portion of the platter
Spindle Motors:
Spindle motors are the devices that spin the platters. They can spin these disks at a set rate, ranging anywhere from 5400 RPM to 7200 RPM! Some spindle motors are located in a position below the head disk assembly, while others are built into the hub of the platters. The modern ones are usually all built into the hub because this takes up less space and thus allows for more platters to be built in. More platters equal more storage space!
Logic Board:
The logic board is located blow the
HDA. It consists of a bunch of chips that control the spindle motors and
the head actuators and that also translates data so that it is usable by
the rest of the computer.
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