Hard Drive
A hard drive is a magnetic storage or solid state device for digital data. Most personal computers contain an internal hard disk that can store large amounts of data, often hundreds of Gigabytes. These are increasingly solid state devices which have no moving parts but can still be expensive for large storage capacity. Sometimes devices have a mixture of the two storage methods.
A hard disk is made up of a number of rotating platters mounted on a spindle which housed in a metal casing. On each side of a platter there is a read/write head. Digital data is written to the disk be means of the 'head' that is flying far less than a hairs' breadth above each platter. The head is fed with data from an electronic circuit also housed inside the metal casing. Digital data is read off the disk by the same head and electronics. Typical Hard disk sizes range from 40Gb to20Tb (Terabyte). They spin at about 7200rpm, sometimes more.
Hard drives are now also popular as an 'external hard drive'. The drive is housed in its own casing and is connected to the computer through an USB port. Some need an additional power supply whilst others are powered directly off the USB port. They are used for backup and archiving as even DVDs are often too small to store the vast amount of data we seem to collect these days in the form of music, films and family photos.
Solid State Devices have no moving parts, data is stored using electronics and the access speed is faster than that of a Hard Disk system. SSD drives can now hold over a Tb of data but they are more expensive.
Central Processing Unit (CPU)
A CPU (Central Processing Unit) is the core of every Personal Computer. Without it, no PC can function.
The CPU is a microchip that is installed on a motherboard and acts as the computer’s brain - performing calculations and coordinating the hardware components.
The speed of the CPU is measured in hertz and refers to the number of cycles per second that the CPU runs at. During each cycle, one instruction can be processed. A CPU with a speed of 100 Megahertz (100 Mhz) can process 100 million jobs per second. One with a speed of 5 Gigahertz (5 Ghz) can process 5 billion jobs per second. Basically, the faster the speed of the CPU, the more instructions can be processed in a given period of time.
Motherboard
The Motherboard is the main printed circuit board in the computer.
It has many sockets into which the CPU, memory (RAM and ROM), cards (sound, graphics, network interface etc) and peripheral devices are connected.
The Motherboard is essential as a means of connecting all of the computer's parts together.
Extra boards, called 'daughter boards' can be plugged into the motherboard.
Random Access Memory
Random access memory (or simply RAM) is the memory in a computer that is used to store computer programs while they are running and also any data the programs need to undertake their task.
Information in the RAM can be read and written quickly in any order - hence the words 'random access'
RAM is emptied every time the computer is turned off. It is also known as volatile memory.
Graphics Card
This is a device which fits into an expansion slot on the Motherboard and can be used to produce high quality displays for your monitor.
Many computer users don't need a high quality display and for them a low power graphics chip will suffice. However for those users who need sharp, clear and perfectly detailed displays, a graphics card is must have piece of hardware.
Graphics cards are designed to perform billions of calculations per second. The job of controlling each pixel on the screen is given over to this card whilst the main CPU just tells it when and what to update.
The graphics card computer chip may also run very hot because of all these calculations and so the card often has a cooling fan fitted.
Input Devices
MOUSE - A mouse is a hand held pointing device that is classed as a manual input device.
A mouse usually has between 1 to 3 buttons which users 'click' in order to point and select objects on the screen. The data from the mouse is transmitted to the computer.
KEYBOARD - A computer keyboard is an input device that enables the user to enter characters (letters, numbers and symbols) into a computer.
The keyboard consists of rows of keys with each key representing a different character.
There are different types of keyboards available, for example, QWERTY keyboards, ergonomic keyboards, braille keyboards.
MICROPHONE - A microphone converts sound into an electrical signal. There are many types of microphone but they all work on the same principle.
Sound is basically rapidly changing air pressure and so a microphone contains a 'diaphragm' that moves back and forth as the sound waves hit it. This movement is detected by some electronics which produces an electrical signal. This signal is then fed into a sound card or audio amplifier.
SCANNER - Scanners, or computer scanners are used to transfer images or text from paper into a digital format that the computer can use.
Once the information has been transferred, it can then be edited, printed, or uploaded to the Internet.
There are two main types of scanner:
- Flat-bed scanner
- Hand-held scanner
TOUCH-PAD - A touch-pad or track-pad is a pointing device featuring a tactile sensor, a specialized surface that can translate the motion and position of a user's fingers to a relative position on the operating system that is made output to the screen.
Output Devices
MONITORS
A monitor is an output device similar to a television screen. It receives signals from the computer and displays that information for the user to view.
There are many different types of monitors available, TFT, LCD etc.
SPEAKER
An output device for handling sound. A speaker takes audio electrical signals and converts them into actual sound that people can hear.
The audio signal may come directly from a sound card installed within a computer. For higher power, this signal may be fed through an audio amplifier before being passed on to the speakers.
Another variation of speaker provides a cable to the earphone jack on the computer to pick up the audio along with an additional USB cable to plug in to supply the power.
PRINTER
A printer is a piece of hardware, often connected to a computer directly or through a local area network (LAN).
Users can print text and pictures on to paper. A printer can also work with digital cameras to print directly without the use of a computer.
There are different types of printers. The ones that you will need to know about for your exam are:
- Laser printers
- Ink-jet printers