# Higher / Intermediate 2 Computer – Systems

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Higher / Intermediate 2 Computer – Systems
Mr Climie Part 1

Data Representation What you will learn here is how a computer that uses an odd number system called binary can still store all kinds of data such as numbers, text, sound or graphics.

How We Change From Binary to Decimal
Representing Numbers How We Change From Binary to Decimal

Why Computers Use Binary
Even if there is a slight drop in voltage it will still be detected as a 1 There are only four rules for addition in binary compared to 100 in decimal [0+0=0 ; 0+1=1 ; 1+0=1; 1+1=10]

Binary to Decimal We can change from our number system, decimal, to the computer number system, binary

Two’s Complement Two's complement is the most popular method of working with negative binary numbers. Do examples. H

Terms Used for Sizes 1Byte = 8 Bits 1KiloByte = 1024 bytes
1MegaByte = 1024 Kbytes 1GigaByte = 1024 Mbytes 1TeraBytes = 1024 GBytes

Representing Real Numbers
What you will learn here is how numbers with fractions, real numbers, are stored on computers. You need to know the terms mantissa and exponent.

Mantissa and Exponent A real number such as can be rewritten as x 103 The is the mantissa The power of 10, the 3, is the exponent

Real Numbers Real numbers are stored by a group of connected bytes of memory. It sets aside a few bytes for the mantissa and a few for the exponent.

Increase the Mantissa If we increase the amount of storage for the mantissa we get a more accurate number stored, but we get a smaller range of numbers.

Increase the Exponent If we increase the amount of storage for the exponent, we increase the range of numbers, but we decrease the accuracy.

Representing Text

Text Representation In this section, you will find out how text is stored on computers and how we can guarantee that what you type is exactly what is printed out or sent to someone else.

Coding Text When we type text into the computer, a numeric code is used to store it as a number.

ASCII This was developed in the 1960’s
Due to peripherals being made by many different makers they needed a common code. American Standard Code for Information Interchange became the common code.

ASCII Control Codes Control codes can be used for device control such as cursor movement, page eject, or changing colours

Character Set This is the set of characters that can be displayed.
If a different language is being used then a different character set may be used. Examples could be Latin set for English Cyrillic for Russian Chinese character set.

Problems With ASCII It is American. There is no code for the £.
There is not a code for European languages and the characters they use.

Unicode This was designed to replace ASCII and have a unique numeric code for every written language. H

Advantage of Unicode The advantage is guaranteed correct communication between Countries Peripherals H

ASCII or Unicode ASCII files are smaller than Unicode files
Unicode has every possible character ASCII is an 8-bit code Unicode is a 16-bit code H

Representing Graphics

Representing Graphics
In this section you will find out how graphics are stored on computers. There are a couple of methods in use and we discuss them.

Graphics Representation
The computer uses two methods to store a graphic on the computer. Bit mapped Records ever single dot or pixel used and stores the pixels directly in the computers memory. Vector Records how the diagram is made up by recording how we would draw the lines and shapes used in the diagram. H

Bit Mapped Graphics The screen is drawn using dots called PIXELS.
Each pixel is connected directly to a set (map) of memory locations.

Bit Map Graphics and Colour
If we use colour, we need more than one bit of memory to record the pixel. This is called bmp graphics. A drawback is the very large size of file that can be produced by some pictures. An advantage is we can edit individual pixels.

Bit Depth or Number of Colours
2n is the amount of colours we can display when we use n bits to store the colours. Sometime said as n-bit depth. 8 – bit depth or 8 bit colour= 256 colours 24 – bit colour (sometimes called true colour) H

Vector Graphics This records ‘how’ to draw the shape by recording the ‘attributes’ of the shape. A big advantage is it takes up very little space to record the picture. H

Example - Circle A circle is drawn knowing the centre co-ordinates, the radius, and the colour of the circumference. Circle1, 200,400, 15, red. H

Bit Mapped Picture Vector Graphic Picture

Graphic File Formats

Graphic File Formats In this section you will find out the different ways graphic programs save their files. No single program or format is the best, they all have different advantages, disadvantages and uses.

Graphic File Formats Use the Internet to research the following graphic file formats BMP JPEG Gif Tiff What it stands for An advantage A disadvantage A likely use of each H

BMP Bit Mapped Pictures
The standard format for Windows based computers. It is a resolution-dependent file format. A picture drawn on a screen of 800x600 pixel will look poor on a screen 1280x768 pixel A drawback is the large file size An advantage is being able to work at individual pixel level H

JPEG JPEG is a format that uses compression.
This can lose data from an image. If you save the compressed file again and again using the compression feature, you will lose detail over time. JPEG files have the extension .Jpeg or .jpg A major advantage is the file size, it is usually far smaller than BMP H

GIF Graphic Interchange Format
Its resolution is low, it is designed for screen only use, making it unsuitable for printing purposes. Animated GIF images are the most common method of creating a moving banner or animation for the web. H

TIFF Tagged Image File Format TIFF is a platform-independent format
The TIFF format was specifically designed for scanned images and use in DTP. Uses bitmapped images There are different versions in use, so it is not commonly used! H

Need for Compression Graphic files can be very large.
Compression is used to make the file size smaller. This may mean the picture loses some quality, but it is a more manageable size.

Memory Used By A Picture
In this section you will find out, by calculation, how much storage is required to store pictures.

Memory Used Calculation
We can calculate how much memory a picture will take up when stored. There are two methods employed, it depends on whether it is displayed on a Screen Or As a photograph

Photograph When we scan a photo we need to know the scan resolution in dots per inch (dpi) and the number of colours or bit depth. We can calculate the memory required to hold it as Area of photo x dpi x dpi x bit depth

Monitor Screen A computer screen uses resolution and bit depth only.
We need to know the screen size in pixels and the bit depth used. Width in pixels times height in pixels times bit depth.

Examples

NOW WE LOOK AT SOFTWARE DEVELOPMENT

Computer Structure

Computer Structure In this section you will find out some detail about the physical parts that make up a computer system. The first part is the main central chip of the computer called the CPU.

Simple Diagram Input Processor Output Main Memory Backing Storage

ALU – Arithmetic Logic Unit
This is the part of the CPU where data is processed and manipulated. The processing consists of Arithmetical operations Logical comparisons It will also include registers to temporarily store the results of calculations.

Arithmetic Unit Most computer calculations involve adding so a specialist arithmetic unit is part of the CPU. 3 times 4 or 3x4 is 3 added together 4 times.

Logic Unit This is special circuits designed to work out comparisons such as A<B Age > 12 (Seats=‘yes’) and (number < 6)

Control Unit This is the part of the CPU that manages the execution of instructions. It fetches each instruction in sequence Decodes the instruction Synchronises the commands Then executes the command This is done by sending out control signals to the other parts of the computer.

Registers These hold Data being processed Instructions being executed
Addresses to be accessed

Internal Busses Higher Content Only

Internal Busses In this section you will find out how the various chips that make up the main section, or motherboard, of the computer can communicate between themselves.

What is a Computer Bus? A bus is a set of physical connections which are used by hardware components in order to communicate with one another. H

The Computer Busses There are three Address bus Data bus Control bus H

Address Bus This transports memory addresses which the processor wants to access in order to read or write data. The size of the address bus will determine how many memory locations can be addressed. The amount of memory accessible for a bus of width n is 2n It is a unidirectional bus. H

Data Bus The data bus is used to transfer data either way between the memory and the CPU. It is a bi-directional bus H

Control Bus It sends signals to other parts of the computer to synchronise their tasks. It also transmits response signals from the hardware. It is a bidirectional bus. H

Example Control Lines Reset - to return a device back to its original state. Interrupt - the processor has to stop doing what it was doing and deal with this new more important task. Read – to initiate the transfer of data from the memory to the processor Write - to initiate the transfer of data from the processor to the memory. H

Fetch Execute Cycle The main task a computer does
It gets an instruction that is stored in the memory of the computer, loads it into the cpu, then does the command it is set. This is called the fetch/execute cyle as it does this repeatedly many times per second.

Fetch Execute Cycle Setup address bus Enable read line
Data transferred using data bus Command decoded Command executed H

Data Storage

Data Storage In this section you will get more details of how a computer stores the data it is using and storing. Also there is a common method used to speed up the access to that data.

Data Storage Computers make use of various styles of storage, they include: Main memory Cache Registers Backing storage

Main Memory There are two styles of memory in use RAM ROM
Random access memory is a type of computer storage whose contents can be accessed in any order ROM Read only memory is memory whose contents can be accessed and read but cannot be easily changed

Use of each type RAM holds the program and data in use at this moment.
ROM will hold parts of the operating system we need when we start the computer.

RAM Random access memory
The contents are lost when the power is off, this means it is volatile. It uses a system of unique memory locations to record where the data is stored.

ROM Read Only Memory ROM cannot be altered.
Any software held in ROM is fixed during manufacture. Typical use is to store a basic set of operating system commands.

What comes next is mainly higher content, Int 2 pupils can investigate how RAM and ROM work.

Cache Memory –1 Cache memory is a relatively small amount (normally less than 1MB) of high speed memory that resides on the CPU H

Cache Memory – 2 Cache memory is designed to supply the CPU with the most frequently requested data and instructions. H

Backing Store Usually magnetic disks, storing data and programs.
Backing store is cheaper but RAM is faster. Can also be re-writeable DVD’s or CD’s, called optical storage. H

Solid State Storage Device
These devices are now very common, this is due to the capacity, physical size and robustness. They can store much more than cd’s and can match DVD’s capacity of 5 Gbytes. H

Addressability The computer assigns numbers or addresses to physical memory locations on boot-up to keep track of the information that the CPU has access to. H

Comparison of memory maps for different O.S.
The O.S. Places into RAM a list of all the known, important locations. This is known as a memory map. H Comparison of memory maps for different O.S.

System Performance

How Fast Is That Computer?
In this section you will find out how we can compare computers in terms of overall speed. We use terms such as powerful and fast but how do we compare them properly.

Clock Speed A computer's system clock resides on the motherboard.
It sends out a signal to all other computer components in sync. Every action in the computer is timed by these clock cycles and takes a certain number of cycles to perform.

Clock Speed as System Performance
This is only a basic measure. We can only compare them if they are made by the same company. Even then they must be from the same ‘family’ of processors.

MIPS Millions of instructions per second.
This measures how many simple instructions can be performed by the CPU in one second. MIPS measures CPU performance only, not the overall system performance.

Flops Floating point operations per second.
This is similar to Mips but it uses real numbers with fractions in the calculations. Is still in use for modern computers.

How Do We Compare Computer Systems?
Mips and Flops look at the processor on its own, but that does not take into account that some disc drives are much faster than others, so we need to be careful how we measure a computers speed. For a full comparison we use application tests which test many different programs and aspects of the whole system.

Application Based Tests
A test that serves as a standard by which computer systems may be compared. This takes into account the complete computer system as well as software. Also known as benchmarks.

More Influences There are more methods of influencing how fast a computer works. These are in the way the computer is designed. On the next page you will learn of some of the ways this can be designed.

Factors That Affect System Performance
Data bus width Wider the better Use of cache memory On board the CPU is better Rate of data transfer to and from peripherals Modern interfaces are much faster, USB2 is 40 times faster than USB1

Other Methods of Increasing System Speed
Increasing clock speeds New parallel processors Increasing memory, 2 or 3 Gb Backing storage capacity1 Tb available

Peripherals

What Is a Peripheral? Peripherals may be internal or external.
Examples of peripherals include printers, monitors, disk drives, scanners and so on. You will find out how we compensate for the difference in speed of the fast computer and the slow peripheral.

Peripheral list Item Mono laser Colour laser Inkjet printer DVD writer
Item Mono laser Colour laser Inkjet printer DVD writer Scanner Internal disc drive external disc drive tft monitor Details Resolution Capacity Speed Compatibility Name Cost

Practical Work The following few slides indicate the type of peripheral you are going to research. Write down the details as you find them. Note we want typical information NOT specific details of an actual peripheral.

1. Typical Characteristics of
Keyboard Mouse Microphone Touchpad

2. Typical Characteristics of
Digital camera Scanner Webcam

3. Typical Characteristics of
Monitor LCD panel Inkjet printer Laser printer Loudspeaker

4. Typical Characteristics of
Hard disc drive Magnetic tape drive CD-rom, CD-R, CD-RW DVD-rom, DVD-R, DVD-RW

Choice of Peripherals A peripheral is hardware that is added to a computer in order to expand its abilities. You can take in to account Resolution Capacity Speed of data transfer Compatibility Cost

Compensating for Speed
Peripherals are slow in comparison to the computer There are methods employed to compensate for these speed differences. Buffers Spoolers

BUFFERS An amount of RAM on the peripheral, used for temporary storage of data that is waiting to be sent to a device, typically a printer. Used to compensate for differences in the rate of flow of data between components of a computer system.

Spoolers A method by which a disc drive can store data and feed it gradually to a printer, which is operating more slowly than the computer. More commonly used in a network.

Interfaces

Interfaces Interfaces are more than just a connector, the wrong choice can slow the speed of the computer system considerably, the right choice can speed it up. Most of the times you do not realise the interface is there, as it should be.

Purpose of an Interface
Interfaces are used to pass data that are different in style but can be used by the equipment connected together by that interface.

Functions of an Interface
Buffering Data format conversion Voltage conversion Protocol conversion Handling of status signals

Buffering This is when a section of RAM is set aside to store the data being transferred. It waits until a complete block of data is created, then transfers the data completely in one block. It then creates a new block of data.

Digital to Analogue Converter
This converts digital signals into analogue signals.

Parallel to Serial Parallel Serial
All bytes of data sent at once in a ‘row’ One cable per bit of data being sent Serial One bit sent at a time, one after the other down the same cable.

Voltage Conversion This may transform the mains AC to DC for the computer peripherals. It may convert the 240volts mains to the 5 volts the computer needs.

Interface Protocol A formal description of the rules and formats used to allow computer and peripheral to work properly together.

Status Registers There will be a special register on the interface that can communicate with the CPU. The status register could hold The printer is out of paper The disc drive is not ready The internet connection can not be made

Wireless This is becoming increasingly more and more common.
There are two styles Bluetooth Wi-Fi

Wi-Fi It can let you use a printer in another room of the house.
You can use peripherals up to quite a long distance away. (30m). You can share a Wi-Fi link with other users or make it secure.

Bluetooth This is also wireless but is much less powerful.
It is designed to allow peripherals of any kind to communicate with others. It only works over about 10 metres distance or so. It is much slower than Wi-Fi.

Computer types A loose description of computer types is Embedded
Palmtop Laptop Desktop Mainframe

Embedded These are incorporated into other devices, rather than being stand alone computers. Examples include digital cameras, mobile phones, music players and almost any kind of industrial  or domestic control system

Palmtop The name for pocket computers of small size, low weight and long battery life. Its disadvantage, comparing to a PC, are reduced functions due to smaller memory and small screen. It is more intended for time planning, listing addresses and notes. Being replaced by Smart Phones such as the iPhone and similar.

Laptop A laptop is a computer that is characterized by mobility.
Its components are similar to a desktop except miniaturized and made for low power consumption. Now being called a portable or notebook.

Desktop Designed to be used by one person only.
The most commonly used style of computer. Easily upgraded and extended..

Mainframe A physically large computer which has an extensive amount of memory and disk space and is able to perform several different tasks simultaneously. It can have hundreds or even thousands of users connected to it.

Computer Task Can you compare the types of computer on
Type of processor Speed of processor Size of main memory Backing storage Input and out put devices

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