Computer Systems Structure of the CPU

Why do computers use binary ? Life would be easy for us if computers used base 10. The symbols 0 to 9 could be represented, for example, by 0 volts through to 9 volts. There would be no need for us to translate between number bases. However, there are a number of disadvantages.

1. Simpler rules for arithmetic to be built into CPU The rules for adding, subtracting, multiplying and dividing that need to be built into the ALU would consist of over 400 instructions, compared to the 10 instructions (approximately) required when binary is used.

2. Voltage fluctuations In decimal any drop in signal would cause a change in the information. For example, if the number 9 is stored in the computer as 9 volts and the voltage drops slightly to 8 volts then the 9 will be changed to an 8. In binary a 0 can be represented by 0 volts and a 1 can be represented by any voltage over 2 volts (usually between 2 to 5 volts).

3. Simplicity of electronic circuitry The circuitry required for binary is simpler as there is either a voltage (1) or no voltage (0). This requires simple electronic circuits which can be only 1 of 2 states (on or off)

4. Easy to represent O’s and 1’s Backing storage medium can easily represent 0’s and 1’s, eg Pits and lands on a CD Positive and Negative magnetic forces on a floppy disk

Categories of Computers

Types Of Computer System There are 5 types of computer system Mainframe Desktop Computer Laptop Computer Palmtop Computer Networked Computer

Mainframe Computer Large computer that can be used for many tasks simultaneously Used by organisations like ISP, SQA, Air Traffic Control May use multiple processors (ie more than 1 CPU) Shares processing time amongst Terminals which are attached to it via a network

Mainframe Terminals These terminals would only be a simple VDU with a keyboard Data would be input and stored at the terminal and then sent to mainframe for processing

Desktop Computer So called because they fit onto a desk Each computer uses a standard QWERTY keyboard along with its own CPU and backing store (normally a hard disc drive) Traditionally CRT monitor now being replaced with TFT or LCD monitor Keyboard and mouse may now be wireless

Other peripherals such as a CDROM drive, soundcard and speakers are used to make the machine fully multimedia Desktop computers usually use a GUI (graphical user interface) such as Windows 98 or Windows XP The processor speed of a desktop is typically 300 MHz or above with 256 Mb RAM

Laptop Computer Laptop computers normally have all the same functions of a desktop computer but use different peripherals for power consumption and weight. Each computer has it’s own Hard disc and processor.

The display for a laptop is normally LCD (liquid crystal display) or TFT(Thin Film Transistor). These displays are very light but are not as easy to see as CRT. The laptop uses specialised input devices such as a touch pad or track ball The keyboard is normally a full keyboard but is shrunk in size

Laptop computers sometimes have an infra red link to allow them to attach to a network or to print. They have a trackpad as an input device

Palmtops - PDA (Personal Digital Assistants) These are small computers that can be held in the hand They have slower processors than a desktop or laptop computer (60 MHz) They have a smaller amount of memory - about 2 to 16 Mb Palmtops may use a touch screen with a stylus to input data and handwriting recognition

Sony Clie stylus

Some palmtops use a very small keyboard LCD panels are the main output of palmtops but these are normally low resolution (400 pixels by 300 pixels) Palmtops do not have backing store instead data is saved onto flash ROM

Investigation of Types of Computer Systems Create a power point presentation giving information on the following types of computers Mainframe Desktop Laptop Palmtop

8 Slides in total 1 slide to describe each type of computer and its use 1 slide to show an up to date photograph and technical specification for that type of computer Do not waste time including animation, sound or fancy backgrounds as we will only be printing the presentation.

Technical Specification Input and Output Devices Backing Storage (type and capacity) Memory (type and amount) Extras (CDWR’s / DVDWR’s, software) Cost

Network Computers A network of computers are computers that are joined together to share resources. These resources may be hardware such as a printer or it may be to share access to data or use a central backing store. The sharing of hardware and software increases the processing load of the main computer on the network (fileserver)

Network Computers Network stations are normally configured as peer to peer or client - server A peer to peer network is normally made up of computers that are joined to one another in a chain. The main use of this is to communicate and share peripherals. These computers are identical to desktop computers except they have a network interface card

Peer to Peer

Client Server Client -Server networks have all the client machines connected to a central computer known as the server. Server Clients

What does the client computer do? Each client computer can be accessed by any user Each client machine has it’s own processor and backing storage (hard disk)

Technical Specification File servers normally have a high speed CPU (533 Mhz) Large backing store (400 Gb Hard Disc) Up to 16GB RAM

Network Vocabulary Node - This is the name given to any connection point to a network. A node may be a computer or piece of hardware. Protocol - This is a set of rules for transmitting and receiving data. The rules must be decided upon before data can be sent

WAN - This is a Wide Area Network WAN - This is a Wide Area Network. It is a network over a large distance (city to city) and normally uses normal phone lines. The speed of transmission is low and the amount of errors is high. LAN - This is a network within a single room or building. The transmission speed is very high 100 Mbps and there are very few errors

Bandwidth - This can be thought of as how many bits can be sent in 1 second. A modem can send about 60,000 bps on a WAN Topology - This is the physical layout of a network Channel – This is the media (usually a cable) along which data is transmitted