A COMPUTER is a complex machine that is capable of performing huge computations at extraordinary speeds. Its processing power is often compared to that of a human brain. Although human intellect is the undoubted winner in this competition, the capabilities of a computer cannot be underestimated. This complex machine, influenced by the design of a human brain, consists of many parts; so let’s continue the discussion from last week.
Hard drive
One of the most essential parts of a computer is the hard drive. Besides storing digital information, the hard drive also contains all of a computer’s operating data, including the operating system (OS). It is considered to be the system’s main storage device.
In cases where multiple hard drives are accessed by the same computer, or where a single hard drive is partitioned (divided) into multiple sectors (areas), the portion that contains the operating system is known as the “start-up” disk. This is the hard drive that the computer will access when it is turned on, booting the operating system, and eventually displaying the user’s familiar desktop interface.
Some users involved in advanced computing prefer to maintain a separate hard drive that contains only the operating system. This can result in a faster start-up and better overall performance. Also, it allows users to change or upgrade their operating systems without the need to transfer other data stored in the computer on other hard drives.
In order to fully understand a hard drive, you have to know how one works physically. Basically, there are discs, one on top of the other, spaced a few millimetres apart. These discs are called platters. Polished to a high mirror shine, and incredibly smooth, they can hold vast amounts of data.
Next, we have the arm. This writes onto and reads data on the disc. It stretches out over the platter, and moves over it from centre to edge, reading and writing data to the platter through its tiny heads, which hover just over the platter. The arm on the average domestic drives can oscillate (swing back and forth with a steady, uninterrupted rhythm) around 50 times per second. Yes! That’s right! 50 times per second! On many high-end machines and those used for complex calculations, this figure can rise into the thousands!
Hard drives use magnetism to store information, just like on old cassette tapes. For that reason, copper heads are used, as they are easy to magnetise and demagnetise, using electricity.
When you save a file, the “write” head on the arm writes the data onto the platter as it spins at high revolutions per minute (RPM), often in the region of 4000 and more.
For this reason, platters are separated into different sectors and tracks. The tracks are the long, circular divisions highlighted here in yellow. They are like ‘tracks’ on music records. Then we have the different sectors, which are small sections of tracks. There are thousands of these, from centre to edge of the platter. One is highlighted blue in the picture.
In operation
When you open a file, programme, or really anything on your PC, the hard drive must find it. So let’s say that you open an image. The CPU will tell the hard drive what you’re looking for. The hard drive will spin extremely fast, and it will find the image in a nano-second (one billionth of a second (10−9 s). It will then “read” the image and send it to the CPU. The time it takes to do this is called the “read time”. Then the CPU takes over and sends the image on its way to your screen.
Let’s say you edited the image. Well now, those changes must be saved. When you click ‘Save’, all of that information is shot to the CPU, which in turn sorts it (processes it) and sends it to the hard drive for storage. The hard drive will spin up, and the arm will use its ‘write’ heads to overwrite the previous image with the new one. Job done!
Common types of hard drives
Parallel ATA (IDE) disks use 40 or 80-pin-wide ribbon cables to transfer multiple bits of data simultaneously (in parallel). They have a cable length limit of 18 inches, and they require five volts of power. Depending on your computer, there may be one or more parallel ATA (or IDE) controller chips on the motherboard. Each parallel ATA channel on a computer motherboard supports two channels, so you can connect two disk drives. However, when both disk drives are connected, they must share the data bandwidth of the connection, so the data rate can potentially be reduced.
Serial ATA (SATA) disks are newer than parallel ATA disk drives. The disk drive mechanisms may be similar, but the interface is significantly different. The SATA hard drive is much faster than the IDE. It also helps with better cooling within the system box by the usage of it much thinner cable, compared to the broad IDE.
Mobile hard drives have become common. These make the transfer of large data possible by allowing users to simply transport the hard drive from one computer to another, where it can be copied to the computer’s internal hard drive, or accessed from the portable hard drive itself. Some portable hard drives consume a small enough level of power to allow them to be powered through their USB connection, which is also their means of connecting to the computer. Such devices are known as “bus powered.”
Other external hard drives may connect to a computer through an IEEE 1394 interface, also known as a “fire-wire” connection. Such high-speed connections can make the performance of an external hard drive nearly as responsive as that of an internal drive that is connected directly to the motherboard.
Hard drives in other devices
One of the major trends in hard drives in recent years involves the integration of hard drives into all manner of electronic devices. Portable music players rarely use traditional recording media, and instead store their music, pictures and other data on hard drives. Cell phones also use hard drives to store phone numbers, call data, music, pictures, and their operating systems.
Hard drives come in different sizes and capacities. One of 100 Gigabytes is capable of holding an average of 15,000 songs. Who knows? You may just have a hard drive lying around somewhere.
