GCSE COMPUTER SCIENCE 8520/2 PAPER 2 + Mark Scheme

GCSE COMPUTER SCIENCE 8520/2 PAPER 2 + Mark Scheme A bit pattern is shown in Figure 1. Figure 1 0 1 . 1 Convert the bit pattern in Figure 1 into decimal. [1 mark] - 78 0 1 . 2 Convert the bit pattern in Figure 1 into hexadecimal. [2 marks] - 1 mark: 4; 1 mark: E; 0 1 . 3 A student's answer to the question "Why is hexadecimal often used instead of binary?" is shown in Figure 2. Figure 2 Because it uses fewer digits it will take up less space in a computer's memory. Explain why the student's answer is incorrect. [2 marks] - 1 mark: The answer is incorrect because number will be represented using binary in a computer's memory; 1 mark: so it will take up the same amount of memory space; 0 1 . 4 Explain how a binary number can be multiplied by 8 by shifting bits. [2 marks] - (Shifting the bit pattern) three places; to the left; Mark as follows: 1 mark: for correct direction of shift 1 mark: for correct number of times to shift 0 1 . 5 Shade one lozenge to indicate which character is represented by the numeric code 70. [1 mark] - 1 mark: B:F; 0 1 . 6 Unicode is an alternative to the ASCII coding system. Describe one advantage and one disadvantage of using Unicode to represent characters instead of using ASCII. [2 marks] - Advantages: Can represent a wider range of characters; Can represent characters from a wider range of languages; Can represent characters used in scientific/mathematical/technical/specialist documents; Disadvantages: (It is likely that Unicode) uses more bits to represent each character; Requires more storage space; Longer transmission time; NE Unicode uses 16/32 bits 0 1 . 7 Using the Huffman code in Figure 3, complete the table to show the Huffman coding for the characters O, SPACE and B. [3 marks] - Character Huffman coding O 111 SPACE 10 B 00110 0 1 . 8 Using Huffman coding the text ZOE SAW A ZEBRA AT THE ZOO can be stored in 83 bits. Calculate how many additional bits are needed to store the same piece of text using ASCII. Show your working. [3 marks] - 7; * 26; = 182 182 - 83; = 99 8; * 26; = 208 208 - 83; = 125 0 2 . 1 Define the term hardware. [1 mark] - Physical/electrical components/parts (of a computer system); 0 2 . 2 "Used to connect different components in the CPU" is a description of which of the following? Shade one lozenge to show the correct answer. [1 mark] - 1 mark: B: Bus; 0 2 . 3 Explain how main memory is used during the fetch-execute cycle. [4 marks] - Program instructions (for current programs) are in the main memory; The next instruction is fetched to the processor from the main memory; Data being used by the instruction being executed may also be in the main memory; To execute the instruction data may need to be fetched/read from the main memory; Data/results may need to be written to the main memory; 0 2 . 4 Increasing the amount of cache memory and changing the type of cache memory can improve the performance of a CPU. State two other ways of improving the performance of a CPU. [2 marks] - 1 mark: increase clock speed; 1 mark: increase number of cores/processors; A. increase bus width A. increase word size A. improve processor architecture A. increase amount of main memory 0 3 . 1 For each of the two statements below shade one lozenge to indicate if the statement is true or false. [2 marks] - 1 mark: 1 st statement; mark is AO1 recall; B:False 1 mark: 2 nd statement; mark is for AO1 understanding; B:False 0 3 . 2 Most modern washing machines are embedded systems. Embedded systems normally have less main memory than non-embedded systems. Describe two other likely differences between the main memory for a washing machine and the main memory for a non-embedded system. [2 marks] - In washing machines, programs are (likely to be) stored in ROM (instead of RAM); Main memory and CPU in washing machines are one component/part of the same chip // main memory is (physically) separate from the CPU on a non-embedded system; Washing machines (likely to) have more ROM than RAM; A. No need for secondary storage in washing machines as programs are kept in ROM; 0 4 . 1 Explain why 36 bits are needed to represent the pixels in the image shown in Figure 4. [2 marks] - Two colours needed in the image so two possible bit patterns needed // one bit per pixel (for black and white image); 36 pixels (so 36 bits needed); 0 4 . 2 How many bits per pixel would need to be used if the image shown in Figure 4 used 4 colours instead of 2? [1 mark] - 2 0 4 . 3 Define the term pixel. [1 mark] - Smallest (addressable) part of a (bitmapped) image; A single dot of colour; 0 5 . 1 Some schools allow teachers to access the school network from their home computers. Give one reason why some schools allow this and one reason why some schools do not allow this. [2 marks] - Reasons for allowing: Teachers can access resources on the school network to allow them to plan lessons at home; Teachers can teach lessons from home (using videoconferencing) if they are not able to get into work (eg travel difficulties); Teachers can access electronic copies of student work so that they do not have to carry marking home; Reasons for not allowing: Data protection issues - schools may not want potentially sensitive student information to be accessed outside of school; To try to help teachers have a work-life balance; Increased security risks as teachers may not have fully-protected computers at home (eg if a teacher does not have anti-virus software on their home computer this may cause problems when they connect their computer to the school network); 0 5 . 2 Describe one difference between a PAN and a LAN. [1 mark] - PANs are centered around one person, LANs cover a limited geographical area / LANs cover a larger area; PANs have one user, LANs (normally) have more than one user; PAN uses Bluetooth, LAN uses alternative protocols / connection methods (A. by example); 0 5 . 3 Give one example of where a PAN could be used. [1 mark] - Wearable computing devices; Connecting headphones to a music player; Connecting pedometer to a mobile phone; 0 5 . 4 "Schools should use a wireless network instead of a wired network". Discuss this statement. [6 marks] - Guidance - Indicative Response Schools should use wired networks: as they need high bandwidth as they make use of a lot of multimedia; as they need high bandwidth / reliable systems as delays in lessons are not acceptable; there is better security on wired networks making it easier for schools to control / monitor how students are using the network; network performance may be poor if there are large numbers of student-owned devices using the school network at any one time; Schools should use wireless networks: • as it allows students to make use of their own portable devices in their learning; • as maintaining a safe learning environment is very important as children are more vulnerable to safety issues (like trailing wires); • it allows computing devices to be used outside of the lesson eg in PE lessons; • as schools have limited budgets and it is cheaper to add extra wireless devices to a school network; • less cable and drilling needed which may save money; • as there are now many devices which don't have wired connection ports and schools may want to be able to use these devices; Extra info from textbook: - A famous example of a wireless network is WiFi - Wireless Fidelity, which is a family of protocols or rules that make the wireless networking run more smoothly - Using wireless connections also means that file transfer speeds are generally slower. - They can be obstructed by walls, ceilings and furniture - They are generally less secure and easier to hack into. Risks: - Criminal Activity - an unauthorised user can use the wireless connection to hack into the network and cause damage by planting viruses, or bring the network to a halt by flooding it with useless traffic (Denial of Service attack) - Bandwidth stealing - by using the Internet connection to download music, games and other software, outside 0 5 . 5 When two computers on a network communicate with each other they need to use the same protocol. Define the term protocol. [2 marks] - 1 mark: a set of rules; 1 mark: that allow two devices to communicate Extra info from textbook: If one computer transmits a stream of binary to another computer, the receiving end needs to know what the rules are. 0 5 . 6 Used to retrieve email stored on a server. [1 mark] - 1 mark: E IMAP; 0 5 . 7 Used to make a payment securely when purchasing goods from a website. [1 mark] - 1 mark: B HTTPS 0 5 . 8 Used to send an email from a client machine to an email server. [1 mark] - 1 mark: D SMTP; 0 5 . 9 TCP/IP is a protocol stack used in networking. There are four layers in the TCP/IP stack. Complete the table by placing the four layers of the TCP/IP stack into order (1 - 4), where 1 is the top layer and 4 is the bottom layer). [3 marks] - Layer Order (1-4) Transport 2 Data Link 4 Network 3 Application 1 0 6 Explain the purpose of an operating system. [4 marks} - The OS is needed to provide an interface between application software / user and hardware; The OS is responsible for memory management; The OS is responsible for processor access // allocating processor time; The OS is needed to handle input/output devices; An operating system is a group of programs that manages the computer's resoucres. It manages all applications running on the computer. 0 7 . 1 Penetration testing is an attack on its own computer system by an organisation to try and identify security weaknesses. Describe one difference between black-box and white-box penetration testing. [1 mark] - With black-box penetration testing the tester does not know how the security systems work, with white-box testing the tester does know how the security systems work 0 7 . 2 Social engineering is often used to try to gain unauthorised access to a computer system. Phishing is a commonly used social engineering technique where emails are sent that pretend to be from a reputable organisation/company to try and obtain personal details. Describe another two social engineering techniques. You should also explain measures that an organisation can take to try to reduce the security risks from phishing and the two other social engineering techniques you have described. [6 marks] - Guidance - Indicative Response for AO1 Pharming - setting up a fake website that looks like an official website for a reputable organisation/company (to try and harvest personal details); Shouldering / shoulder surfing - observing a legitimate user entering (security) data into a computer system; Baiting - leaving a malware infected portable storage device around hoping that a legitimate user will insert it into the computer system; Pretexting/blagging - persuading (often by use of a faked scenario) legitimate users to divulge personal data; Guidance - Indicative Response for AO2 To reduce risks from phishing: allow emails only from known sources; To reduce risks from pharming: web filters; To reduce risks from shouldering: careful placement of terminals; To reduce risks from baiting: lock down systems so portable storage devices are not usable; To reduce risks from blagging: use of security details which cannot be accidentally divulged eg biometric measures; General strategies for reducing the risks from social engineering: train/educate users; making use of appropriate security protocols for handling sensitive/security data; performing frequent (unannounced) tests of security measures; 0 8 . 1 Calculate how many megabytes there are in 4GB. Show your working. [2 marks] - 1000 × 4 // 4000;; 0 8 . 2 An SD card is a type of solid state storage. State two advantages of solid state storage compared to magnetic storage. [2 marks] - Lighter; Smaller; Uses less power; More robust; Generates less heat; Quieter; 0 8 . 3 Many modern desktop computers have both solid state drives and magnetic hard disk drives. Give two reasons why desktop computers have a magnetic hard disk drive and a solid state drive instead of having just a solid state drive. [2 marks] - Using just solid state would cost much more; Can get higher storage capacity by including magnetic hard disk; 0 8 . 4 Describe how data is stored on, and read from, a magnetic hard disk. [4 marks] - On a hard disk binary data represented by tiny magnetised regions; where the magnetic orientation in one direction represent 0, and the other direction represents 1; When reading data the read/write head is moved (to be over correct track); and the platter/disk spins round; A whole sector/block read in one go (by the read/write head); 0 8 . 5 In recent years, there has been a large growth in the use of cloud storage. Discuss the advantages and disadvantages of using cloud storage. In your answer you should include an explanation of the reasons for the large growth in recent years and consider any legal, ethical and environmental issues related to the use of cloud storage. [9 marks] - Guidance - Indicative Response (reasons for growth) Higher bandwidth mobile networks (eg 4G); Increased availability of mobile devices; Reduction in cost of large capacity storage devices; Improvements in network security; People have a higher level of trust in cloud storage; Improvements in web browser software; Increased availability of supercomputers (for cloud processing); Companies have managed to develop business models based on cloud computing that allow them to make a profit; Guidance - Indicative Response (advantages of cloud storage) Enables user to access their data from more places/devices; Enables user to more easily share data with others (can make parts of their cloud storage publically available); Increases the amount of storage available; Reduced cost of computing devices for users as no need for as much built-in secondary storage; Guidance - Indicative Response (disadvantages of cloud storage) Increased security risks; Relies on access to high-bandwidth network connection; Could potentially cost more due to ongoing costs; Reliance on company providing the cloud service; Increased chance of others accessing personal data (data privacy issues); ------------------------------------------------------------------------- Written answer: There are many reasons for the growth and increased use of cloud storage. The term 'cloud storage' refers to saving data in an off-site storage system maintained by a third party, for example Dropbox, Google or Microsoft. Instead of saving data on your computer's hard drive or other local storage device, you save it in a remote storage facility and access it via the internet. This means that there is a reduction in the costs of large capacity storage devices, and since there have been improvements in network security, it means that people have a higher level of trust in cl