2 Data RepresentationWhat 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.
3 How We Change From Binary to Decimal Representing NumbersHow We Change From Binary to Decimal
4 Why Computers Use Binary Even if there is a slight drop in voltage it will still be detected as a 1There 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]
5 Binary to DecimalWe can change from our number system, decimal, to the computer number system, binary
6 Two’s ComplementTwo's complement is the most popular method of working with negative binary numbers.Do examples.H
14 Text RepresentationIn 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.
15 Coding TextWhen we type text into the computer, a numeric code is used to store it as a number.
16 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.
17 ASCII Control CodesControl codes can be used for device control such as cursor movement, page eject, or changing colours
18 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 beLatin set for EnglishCyrillic for RussianChinese character set.
19 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.
20 UnicodeThis was designed to replace ASCII and have a unique numeric code for every written language.H
21 Advantage of UnicodeThe advantage is guaranteed correct communication betweenCountriesPeripheralsH
22 ASCII or Unicode ASCII files are smaller than Unicode files Unicode has every possible characterASCII is an 8-bit codeUnicode is a 16-bit codeH
24 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.
25 Graphics Representation The computer uses two methods to store a graphic on the computer.Bit mappedRecords ever single dot or pixel used and stores the pixels directly in the computers memory.VectorRecords how the diagram is made up by recording how we would draw the lines and shapes used in the diagram.H
26 Bit Mapped Graphics The screen is drawn using dots called PIXELS. Each pixel is connected directly to a set (map) of memory locations.
27 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.
28 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 colours24 – bit colour (sometimes called true colour)H
29 Vector GraphicsThis 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
30 Example - CircleA circle is drawn knowing the centre co-ordinates, the radius, and the colour of the circumference.Circle1, 200,400, 15, red.H
33 Graphic File FormatsIn 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.
34 Graphic File FormatsUse the Internet to research the following graphic file formatsBMPJPEGGifTiffWhat it stands forAn advantageA disadvantageA likely use of eachH
35 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 pixelA drawback is the large file sizeAn advantage is being able to work at individual pixel levelH
36 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 .jpgA major advantage is the file size, it is usually far smaller than BMPH
37 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
38 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 imagesThere are different versions in use, so it is not commonly used!H
39 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.
40 Memory Used By A Picture In this section you will find out, by calculation, how much storage is required to store pictures.
41 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 aScreenOrAs a photograph
42 PhotographWhen 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 asArea of photo x dpi x dpi x bit depth
43 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.
49 ALU – Arithmetic Logic Unit This is the part of the CPU where data is processed and manipulated.The processing consists ofArithmetical operationsLogical comparisonsIt will also include registers to temporarily store the results of calculations.
50 Arithmetic UnitMost 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.
51 Logic UnitThis is special circuits designed to work out comparisons such asA<BAge > 12(Seats=‘yes’) and (number < 6)
52 Control UnitThis is the part of the CPU that manages the execution of instructions.It fetches each instruction in sequenceDecodes the instructionSynchronises the commandsThen executes the commandThis is done by sending out control signals to the other parts of the computer.
53 Registers These hold Data being processed Instructions being executed Addresses to be accessed
55 Internal BussesIn 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.
56 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
57 The Computer BussesThere are threeAddress busData busControl busH
58 Address BusThis 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 2nIt is a unidirectional bus.H
59 Data BusThe data bus is used to transfer data either way between the memory and the CPU.It is a bi-directional busH
60 Control BusIt 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
61 Example Control LinesReset - 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 processorWrite - to initiate the transfer of data from the processor to the memory.H
62 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.
63 Fetch Execute Cycle Setup address bus Enable read line Data transferred using data busCommand decodedCommand executedH
65 Data StorageIn 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.
66 Data StorageComputers make use of various styles of storage, they include:Main memoryCacheRegistersBacking storage
67 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 orderROMRead only memory is memory whose contents can be accessed and read but cannot be easily changed
69 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.
70 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.
71 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.
72 What comes next is mainly higher content, Int 2 pupils can investigate how RAM and ROM work.
73 Cache Memory –1Cache memory is a relatively small amount (normally less than 1MB) of high speed memory that resides on the CPUH
74 Cache Memory – 2Cache memory is designed to supply the CPU with the most frequently requested data and instructions.H
75 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
76 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
77 AddressabilityThe 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
78 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.HComparison of memory maps for different O.S.
80 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.
81 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.
82 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.
83 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.
84 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.
85 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.
86 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.
87 More InfluencesThere 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.
88 Factors That Affect System Performance Data bus widthWider the betterUse of cache memoryOn board the CPU is betterRate of data transfer to and from peripheralsModern interfaces are much faster, USB2 is 40 times faster than USB1
89 Other Methods of Increasing System Speed Increasing clock speedsNew parallel processorsIncreasing memory, 2 or 3 GbBacking storage capacity1 Tb available
91 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.
93 Practical WorkThe 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.
94 1. Typical Characteristics of KeyboardMouseMicrophoneTouchpad
95 2. Typical Characteristics of Digital cameraScannerWebcam
96 3. Typical Characteristics of MonitorLCD panelInkjet printerLaser printerLoudspeaker
97 4. Typical Characteristics of Hard disc driveMagnetic tape driveCD-rom, CD-R, CD-RWDVD-rom, DVD-R, DVD-RW
98 Choice of PeripheralsA peripheral is hardware that is added to a computer in order to expand its abilities.You can take in to accountResolutionCapacitySpeed of data transferCompatibilityCost
99 Compensating for Speed Peripherals are slow in comparison to the computerThere are methods employed to compensate for these speed differences.BuffersSpoolers
100 BUFFERSAn 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.
101 SpoolersA 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.
103 InterfacesInterfaces 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.
104 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.
105 Functions of an Interface BufferingData format conversionVoltage conversionProtocol conversionHandling of status signals
106 BufferingThis 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.
107 Digital to Analogue Converter This converts digital signals into analogue signals.
108 Parallel to Serial Parallel Serial All bytes of data sent at once in a ‘row’One cable per bit of data being sentSerialOne bit sent at a time, one after the other down the same cable.
109 Voltage ConversionThis may transform the mains AC to DC for the computer peripherals.It may convert the 240volts mains to the 5 volts the computer needs.
110 Interface ProtocolA formal description of the rules and formats used to allow computer and peripheral to work properly together.
111 Status RegistersThere will be a special register on the interface that can communicate with the CPU.The status register could holdThe printer is out of paperThe disc drive is not readyThe internet connection can not be made
112 Wireless This is becoming increasingly more and more common. There are two stylesBluetoothWi-Fi
113 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.
114 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.
115 Computer types A loose description of computer types is Embedded PalmtopLaptopDesktopMainframe
116 EmbeddedThese 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
117 PalmtopThe 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.
118 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.
119 Desktop Designed to be used by one person only. The most commonly used style of computer.Easily upgraded and extended..
120 MainframeA 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.
121 Computer Task Can you compare the types of computer on Type of processorSpeed of processorSize of main memoryBacking storageInput and out put devices