Wikijunior:How Things Work/Hard Drive

When was it invented?
Hard disks were first invented in the 1950s and were initially called fixed disks or 'Winchesters' (the name of a popular IBM offering introduced in 1972.) The first magnetic hard disc for storage was the IBM 305 RAMAC which appeared in 1956. RAMAC (Random Access Method of Accounting and Control) quickly became the industry standard. For years hard drives were confined to mainframes and servers.

How does it get power?
The hard disk gets its power from one of the variable electrical output leads of the SMPS (switch mode power supply) of the computer.

How does it work?
First take a close look at the hard drive image here. This will give you a great idea of how each part is working together inside a hard drive.

Imagine a bunch of bar magnets all in a row, with the ends sticking towards you. Imagine that the first one has the north side sticking up, then the next 2 have south sticking up, and then 5 have north sticking up again. If you place a bunch of magnets together like this, you can start creating a code. A code created out of only north and south signals. In fact, computers are based on a very simple code based on only 0s and 1s called binary. North and South can be translated into 0 and 1 very easily.

A hard disk turns this line of magnets into a disk. Imagine spinning the long line of magnets like a thread around, like rolling up a piece of paper. To read the hard disk, all you have to do is spin the disk, and place another very small detection magnet close to it. The detection magnet is called a magneto-resistive read sensor. From the pattern of north and south, you can translate the code from "North and South" into everything on a computer.

The hard disk is also able to flip the magnets any time, so it can turn a magnet from "north" into "south" very easily. This allows it to not only read the disk, but write to it. Basically, it can change the "code" of north-south any time the computer wants it to.

When computers do this, they spin the disk very fast. They can read the code millions of times a second. Much work has been done to help make the disk spin faster and faster.

How dangerous is it?
Not very dangerous unless you open one up while attached to a power supply. A big mistake!

What does it do?
It is a mass storage device which can be used to store operating systems and a number of pieces of software. It is one of the main components of Desktop and Laptop computers. One hard disk can be partitioned to create a number of different virtual disks. Each such virtual disk can store (and work) a different operating system. The newer hard disks are much smaller than the original ones, but can store much much more than their ancestors. Not forgetting about their speeds. The newer hard disks can fetch data (stored in them) at the wink of an eye.... sometimes even faster.

How does it vary?
Not that many hard drives vary, except for the amount of data that they hold. There are different types of hard drives, like external hard drives and internal hard drives. Some types of hard drives are explained below.

Parallel Advanced Technology Attachment (PATA)
These types of drives are also known as Integrated Drive Electronics (IDE) and Enhanced Integrated Drive Electronics (EIDE) drives. These hard drives are very slow.

Serial ATA (SATA)
SATA drives are more efficient, and use less power than PATA drives. They are also faster than the PATA drives.

Solid State Drives (SSD)
These hard disks, unlike the other types, don't consist of moving components. The other hard drives explained above comprise of a spinning magnetic disk that performs the function of storing data, but SSDs use semi-conductors for this purpose. Since there are no moving components, these hard disks are much faster than the other drives.

How has it changed the world?
Hard drives enable computers and other electronic devices such as MP3 players to store massive amounts of information for use later.

Hard drives have allowed computer programmers to build enormously complex programs and store them for use on computers. Complex programs such as the one you are using to read this would not have been available prior to the introduction of hard drives.

Before hard drives were used in computers, popular storage mediums included cardboard cards, paper tape (with holes punched in it), magnetic tape, and magnetic tape formed into disks called floppy disks.

As computer programs have increased in size, hard drives have had to also increase in size to store the data.

What idea(s) and/or inventions had to be developed before it could be created?

 * The computer
 * Magnetic data storage