Stonelaw High School Computing Science BGE - Computer Systems
Contents Computer Systems... 3 Computer Systems... 3 Hardware & Software... 3 Data Representation... 3 Representing Positive Integers... 3 ASCII... 4 ASCII Table (Extract)... 5 ASCII (Continued)... 6 Bitmap... 7 Resolution... 7 Advantages of Bitmaps... 8 Disadvantages of Bitmaps... 8 Encryption & Compression... 9 Encryption... 9 File Compression... 9 Computer Structure... 10 Central Processing Unit... 10 Arithmetic & Logic Unit... 10 Control Unit... 10 Registers... 10 Memory Unit - RAM... 11 Program Execution... 11 Networks... 11 Types of Network... 12 Local Area Network (LAN)... 12 Wide Area Network (WAN)... 12 Connecting to a Network... 12 How Computers Communicate and Share Information... 13 How to study for Computer Systems... 13 Stonelaw High School Page 2
Computer Systems Computer Systems A computer system is the term used to describe the computer, its software and everything connected to it. Hardware & Software Hardware is the physical parts of the computer system the parts that you can touch and see (Monitor, Keyboard, Mouse etc.) Software is the programs or applications (apps) that can be run on a computer system (Windows 10, Microsoft Word, Google Chrome etc.) Data Representation There are different types data stored and processed in a computer system, including: numbers text graphics Regardless of the type of data being stored they are all represented inside the computer using binary (sometimes called machine code). Binary is a two-state system which uses patterns of 1s and 0s to represent data. The binary system works as follows: Binary Value Voltage Present 1 Low Voltage Present 0 Representing Positive Integers Integers are whole numbers including positive and negative values. Zero is also an integer. Examples of integers include: 113-78 0 255-126 1 Decimal numbers can be converted to binary using the following table (8-bit number conversion): 128 64 32 16 8 4 2 1 Decimal value Stonelaw High School Page 3
Decimal to binary example: Convert the decimal value of 85 to binary Put a 1in the columns that add up to 85 128 64 32 16 8 4 2 1 0 1 0 1 0 1 0 1 Starting at 128 (far left of the table): Question Answer Action 1. Can 128 be subtracted from 85? No Put a 0 in the box 2. Can 64 be subtracted from 85? Yes Put a 1 in the box (85-64 = 21 remaining) 3. Can 32 be subtracted from 21 No Put a 0 in the box 4. Can 16 be subtracted from 21 Yes Put a 1 in the box (21-16 = 5 remaining) 5. Can 8 be subtracted from 5 No Put a 0 in the box 6. Can 4 be subtracted from 5 Yes Put a 1 in the box (5-4 = 1 remaining) 7. Can 2 be subtracted from 1 No Put a 0 in the box 8. Can 1 be subtracted from 1 Yes Put a 1 in the box (1-1 = 0 remaining) Binary to decimal example: Binary numbers can be converted to decimal using the same table. Convert the binary value 10101010 to decimal Add the columns together that have a 1 in them 128 64 32 16 8 4 2 1 1 0 1 0 1 0 1 0 128 + 32 + 8 + 2 = 169 Range of numbers Using 8 bits the 256 numbers can be stored, 0 to 255: 8 bits = 2 8 = 256 or Number of bits = 2 Num ber of bits = Number of values which can be stored ASCII ASCII (American Standard Code for Information Interchange) is used to store and represent text in a computer system. Each character is assigned a unique code which identifies it. Extended ASCII uses 8-bits to store each character. This allows us to represent 256 characters. The extended ASCII table looks like this: Stonelaw High School Page 4
ASCII Table (Extract) Letter ASCII Code Letter ASCII Code a 097 A 065 b 098 B 066 c 099 C 067 d 100 D 068 e 101 E 069 f 102 F 070 g 103 G 071 h 104 H 072 i 105 I 073 j 106 J 074 k 107 K 075 l 108 L 076 m 109 M 077 n 110 N 078 o 111 O 079 p 112 P 080 q 113 Q 081 r 114 R 082 s 115 S 083 t 116 T 084 u 117 U 085 v 118 V 086 w 119 W 087 x 120 X 088 y 121 Y 089 z 122 Z 090 Space 032, 044! 033 _ 045 034. 046
ASCII (Continued) The first 32 characters in the ASCII table are known as control characters. Control characters are non-printable, that is, they don t appear on the screen or on your print outs. The most common control characters are: Delete Escape Return Tab Advantages of ASCII Each character only takes up 8-bits (1 Byte) of storage Universally recognised Disadvantages of ASCII Not all the worlds languages can be represented using ASCII
16 bits Bitmap Bitmap images are stored on computers using the bitmap format. An uncompressed bitmap contains data about each pixel that makes up the image on the screen. A pixel (short for picture element) are small dots that make up an image. In its simplest form a bitmap of a black and white image, is a grid of pixels where each pixel would be represented by a single bit which would be set to a 1 or 0. 0 0 1 0 0 0 1 0 0 0 1 0 0 0 0 0 Is 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 stored 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 as 0 0 1 1 1 1 1 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0 1 0 0 Bitmap 16 bits Resolution The quality of a graphic is determined by the number of pixels used. The larger the number of the pixels used within a fixed space then the better the quality of the graphic. The first photograph of the car is taken at a higher resolution than the second photograph. 300 dpi (188K) 72 dpi (11K) For example; a bitmap image with a resolution of 3840x2160 will be better quality than a bitmap image with a resolution of 1280x720. Stonelaw High School Page 7
Advantages of Bitmaps Images can be realistic (photographic). Images can be edited at pixel level. Disadvantages of Bitmaps File size can be large. Scaling causes pixelization. Individual objects can t be edited (must be done at pixel level). Stonelaw High School Page 8
Encryption & Compression Encryption Encryption is used to prevent unauthorised access to sensitive electronic data. The electronic information is converted into a coded message so that when it is communicated it can t be intercepted and read by a third party. Encryption is achieved by using a key (or code) to convert the information into an unreadable code. The recipient of the information then decrypts the communication back into the original information. Encrypted Message Original Message Original Message File Compression File compression is the process used to reduce the size of files, there are two types of file compression: Lossy Compression The lossy method of compression is a method in which some of the data is discarded. There is generally a trade-off between file size and quality when using lossy compression. Original Image 75% Compression 50% Compression Lossless Compression The lossless method of compression is a method in which the file size is reduced but none of the original data is lost or discarded. Original Image Compressed Image No noticeable difference in quality File compression is used on multimedia files to reduce storage space and speed up download and transfer times. However, compressing files can be time consuming and often some of the original data is lost. Stonelaw High School Page 9
Computer Structure The basic structure of a computer system can be shown using the von Neumann architecture: Backing Storage Central Processing Unit Control Unit Input Devices Arithmetic Logic Unit Registers Output Devices Memory Unit Central Processing Unit The Central Processing Unit (sometimes called the CPU or Processor) is a silicon chip within the computer which is the brain of the computer. The processors can carry out billions of instructions per second. The processor can be split into three components: Arithmetic & Logic Unit The Arithmetic & Logic unit (ALU) is responsible for: Performing arithmetic calculations Carrying out logical comparisons (AND, OR, NOT) Control Unit The Control Unit (CU) is responsible for: Controlling the order of instructions and operations for the entire computer system Registers The registers are storage locations which are in the processor. They are used for: Storing instructions which are being carried out. Stores data being processed Stores memory addresses being accessed Stonelaw High School Page 10
Memory Unit - RAM Random Access Memory (RAM) is where all the programs and data that you are currently using are stored. Data and instructions are only stored in RAM temporarily if you close the program or power the computer off data and instructions will be lost. Memory in a computer is split up into storage locations. Each memory location has a unique address. Program Execution A program is a set of instructions which the computer executes (runs). Examples of some of programs we have used include: Microsoft Word Google Chrome Microsoft PowerPoint The instructions to run these programs are stored in the computer s memory using binary. All programs are run (or executed) by the computer using the fetch execute method: 1. Repeat until all the instructions have been executed. 2. The Central Processing Unit (CPU) receives an instruction from the computer s memory. 3. The instruction is then decoded by the CPU and executed. 4. The next instruction is retrieved from memory for execution. Networks A computer network is a set of computer systems linked together so that they can send messages, and share programs and data with each other. These networks can have any number of devices connected to them, such as computers and printers. For example, a home network might have a handful of devices connected while a school network could have several hundred. Computers that are not connected to any network are called stand-alone computers. Stonelaw High School Page 11
Types of Network There are two main types of networks, the differences between them depends on the physical distance between the computer systems connected. Local Area Network (LAN) A LAN covers a small physical area such as a room or building. In a LAN all of the connected computer systems are usually owned by a single company of an organisation such as a school. Home networks and school networks are likely to be a LANs. Wide Area Network (WAN) A WAN covers a much larger physical area such as a city, country and international regions such as Europe. The most well-known and well-used WAN is the Internet, where millions of computer systems are connected. Some companies, especially those that work in many different countries, might have their own WAN for their computers. Connecting to a Network Computers can connect to a network either physically or through wireless, depending on the network card installed in the machine. A Network Interface Card (NIC) allows the computer to connect to the network physically using Ethernet cables. A Wireless Network Interface Card (WNIC) allows the computer to connect to the network using wireless radio signals. + Network Interface Card (NIC) Ethernet Cable Wireless Network Interface Card (WNIC) Stonelaw High School Page 12
How Computers Communicate and Share Information Computers on a network communicate with each other by splitting the data into smaller packets of data. The packets of data are sent from one computer to the other. Each packet contains the data to be sent as well as the addresses of the computers on the network that it is communicating with. This way the packet knows the network address of the computer that sent it, known as the sender, and the address of the computer it needs to go to, known as the receiver. Streaming services such as Netflix use this method to allow users to download and watch films and TV shows. Data: Email Sender Address: 192.0.0.1 Receiver Address: 192.0.0.2 Address: 192.0.0.1 Address: 192.0.0.2 How to study for Computer Systems To help you to study for Computer Systems and learn the technical terms and their meanings the following studying techniques can be used: Pay attention in class Read your notes at home Summarise notes in your own words Write keywords or technical terms on labels and stick them around your house Teach the topic area to someone else Choose a topic and write down as much information about it as you can Create a mind map Create a study PowerPoint Ask your teacher questions when you don t understand Complete all homework tasks ask your teacher for help if required Make flash cards up of topics or terms you are struggling to remember Get someone else to ask you questions (you could use homework questions or questions used in class) Read some topics out loud Create a set of cards with questions on one side and answers on the other. Look over homework tasks Use the IT rooms at lunchtime for studying Stonelaw High School Page 13