Central Processing Unit
The CPU is the brains within your computer. It performs most of the calculations within the computer and is responsible for the smooth running of your operating system (Microsoft Windows) as well as your application programs, such as word-processors, spreadsheets and databases. There is a small amount of memory associated with the CPU, which it uses to perform these operations. It also accesses and uses the main memory (RAM - Random Access Memory) within your computer. In many ways, the CPU is the single most important item within your computer which governs the overall speed of your computer. The CPU's speed is measured in MHz of GHz. This relates to the frequency at which the CPU runs and the higher the MHz (or GHz) rating of your CPU the faster your computer will run. To give you some indication of how PCs have advanced over the years, the original IBM PC released in 1981 ran at less than 5 MHz while modern PCs can run at speeds well in excess of 2000 MHz (2 GHz). Note that 1000 MHz is the same a 1 GHz
You can store data on your hard disk, while data which is being processed is stored in RAM (Random Access Memory). Data which is stored on a hard disk can be permanent, while data in RAM is only temporary. Normally when people talk about memory in relation to a PC, they are talking about RAM
Random Access Memory (RAM) is the main 'working' memory used by the computer. When the operating system loads from disk when you first switch on the computer, it is copied into RAM Microsoft Windows based computer will operate faster if you install more RAM Data and programs stored in RAM are volatile (i.e. the information is lost when you switch off the computer)
What is ROM
Read Only Memory (ROM) as the name suggests is a special type of memory chip which holds software which can be read but not written to. A good example is the ROM-BIOS chip, which contains read-only software. Often network cards and video cards also contain ROM chips
The 'Read Only Memory Basic Input Output System' chip is a chip located on the computer's system (mother) board, which contains software. This software performs a variety of tasks. When you first switch on the computer the ROM-BIOS software performs a self-diagnostic to check that the computer is working OK. This software then loads your operating system from the disk into the RAM
Most modern computers are actually supplied with flash BIOS rather than ROM-BIOS. This chip contains exactly the same type of in-built software, but has the advantage that the software on the chip can be upgraded. This upgrade is achieved by simply running a small program supplied by the computer manufacturer
Video (graphics) memory
The picture which you see on your screen is a form of data and this data has to be stored somewhere. The on-screen pictures are held in special memory chips called video memory chips; these chips are usually located on the video card. A modern computer will be supplied with several Megabytes of video memory
How computer memory is measured
The simplest unit of memory is the bit. A single bit is equal to either a numerical 1 or 0 at any given time. Each bit of memory is like a tiny switch that the computer can turn on or off: on equals 1 and off equals 0. This system is called the binary system of counting.
Modern computers contain many bits of memory, referred to in increasingly large units:
A byte is 8 bits.
A kilobyte (KB) is 1,024 bytes. Computers use binary arithmetic, which makes 1,024 a "round" number in computing terms.
A megabyte (MB) is 1,024KB, or roughly 1 million bytes.
A gigabyte (GB) is 1,024MB, or roughly 1 billion bytes.
A terabyte (TB) is 1,024GB, or roughly 1 trillion bytes.
A byte will hold a single character of the alphabet; each letter is represented by a particular code of 1s and 0s. (For example, the letter "A" is usually stored as 01000001 in "computer language.")
A page of text will take about 5KB to store.
This entire book takes up about 5MB of RAM.
A GB of text would come to about 2,000 books, a good-sized personal library.
The Library of Congress holds nearly 25 million books. That's about 12.5TB of text.
Of course, not all the information stored on your computer is in the form of text. Programs, graphics, sounds, movies, drawings, and other forms of information all take up RAM when they're current in your computer. A typical application might occupy anywhere from 100KB to 100MB of RAM while it's running
The mouse came into common use on a PC with the introduction of the Microsoft Windows operating system. Before this, the operating system (DOS) would normally be controlled via the keyboard. These days it is vital to be a competent mouse user. There are many different types of mice, a commonly used model now has a small wheel on it which when combined with the correct software allows additional functionality and fine control over the use of your applications
The keyboard is still the commonest way of entering information into a computer. There are a number of different types, including those specially designed for use with Microsoft Windows. The quality of the keyboard is often overlooked when buying a PC; it should be robust and easy to use
A tracker ball is an alternative to the traditional mouse and favored by graphic designers. Tracker balls often give much finer control over the movement of the items on the screen. They may take a while to get used to if you are used to the traditional mouse, but offer a lot in terms of added flexibility
A scanner allows you to scan printed material and convert it into a file format which may be used within the PC. You can scan pictures and then manipulate these inside the PC using a graphics application of your choice. In addition, you can scan printed text and convert this not just to a picture of the text but also to, actual text which can be manipulated and edited as text within your word-processor. There are a number of specialist programs, generically called OCR (Optical Character Recognition) programs which are specifically designed for converting printed text into editable text within your applications
A touch pad is a desktop device and responds to pressure. Used in conjunction with a special pen they can be used by graphic artists wishing to create original, digital artwork
A light pen is used to allow users to point to areas on a screen and is often used to select menu choices
Joysticks many games require a joystick for the proper playing of the game. There are many different types
Voice input for PCs (microphones) Early voice recognition systems offered very poor results, due to the limitations of the software combined with hardware limitations. It takes an awful lot of CPU processing power to convert the spoken word into text which appears on the screen. Things are changing rapidly however and recent systems allow you to talk to a PC and see text appear on the screen. Most of these systems require an initial training period, where you train the software to respond to your particular voice. Whilst still not perfect this is a key technology of the future
Web Cams You can now use a small digital movie camera (a Web cam) mounted on the PC monitor to allow two-way communication involving not just text communication but sound and video communication as well
A digital camera can be used in the same way a traditional camera can, but instead of storing images on rolls of film which require developing, the images are stored digitally in memory housed within the camera. These pictures can easily be transferred to your computer and then manipulated within any graphics programs which you have installed on your computer. Currently they are limited by the quality of the image recorded and the number of pictures which you may store within the camera
The VDU (Visual Display Unit) is the computer screen used for outputting information in an understandable format for humans. Remember that at the end of the day the computer works in binary code (a series of on/off impulses). It is hard to realize that the original electronic computers did not have a screen
Flat screen monitors Traditional computer monitors are based on the same sort of technology which is used within a television screen. More recently, flat screen computer monitors have become available. These take up a lot less room on a desk and use less energy than the traditional, more bulky monitors
Computer presentation projection devices These are projection devices which can be attached to your computer and are useful for displaying presentations to a group of people. They are best used in combination with presentation programs, such as Microsoft PowerPoint. They are used within education and are also very popular for sales presentations. The price of these devices has dropped dramatically recently. When purchasing one of these devices the two things to look out for are the resolution (go for a minimum of XGA) and the brightness of the lamp (the brighter the better). Other factors to be aware of are the quietness (or otherwise) of the device, as well as the cost of replacement bulbs
Laser printers produce high print quality at high speed. They are called "laser printers" due to the fact that they contain a small laser within them. There is a wide range of laser printer manufacturers
Color laser printers originally, most laser printers would only print in black and white (mono). More recently color laser printers have dropped in price and are entering wide spread use. While many of these produce excellent results, you should be aware of the fact that the "price per page", especially if you are using a lot of color on a page can be very high compared to the cost of printing in black and white
Inkjet printers work by using tiny jets to spray ink onto the paper. Inkjet printers are very quiet in operation and produce print quality comparable to that of laser printers, though laser printers still have the edge in terms of speed. Inkjet printers are ideal for low volume printing where high quality print is required and speed is not a high priority, e.g. printing letters in a small office or in the home
Dot matrix printers work by firing a row of pins through an ink ribbon onto the paper. The more pins the print head has the higher the quality of the print, most modern dot matrix printers have 24 pins. Unfortunately, dot matrix printers can generate a lot of noise and do not produce a very high quality of print, especially when printing graphics. As a result, the inkjet printer has now largely replaced the dot matrix printer. Dot matrix printers are used for high volume / low quality printing, e.g. printing company pay slips
A plotter is an output device similar to a printer, but normally allows you to print larger images. Their use is common in the design and research sector
Speakers Most computers are sold with the capability to add a pair of speakers to your system unit. In fact, in some cases, the monitor may have speakers built directly into the unit. This enhances the value of educational and presentation products and can now be considered a standard PC component
Some devices are both input and output devices. A modem can be used for downloading information from web sites and receiving emails. It can also be used for uploading and sending emails. A touch screen can display a menu system (output device), and accept input when people touch the menus displayed on the screen