Cambridge A Level Computer Science 9608 — 2018 Oct/Nov Paper 1 · Variant 3

* 3 4 1 3 6 3 1 8 8 5 * This document consists of 14 printed pages and 2 blank pages. DC (SC/SW) 144491/4 © UCLES 2018 [Turn over Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level COMPUTER SCIENCE 9608/13 Paper 1 Theory Fundamentals October/November 2018 1 hour 30 minutes Candidates answer on the Question Paper. No Additional Materials are required. No calculators allowed. READ THESE INSTRUCTIONS FIRST Write your Centre number, candidate number and name in the spaces at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, glue or correction fluid. DO NOT WRITE IN ANY BARCODES. Answer all questions. No marks will be awarded for using brand names of software packages or hardware. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. The maximum number of marks is 75.

2 9608/13/O/N/18 © UCLES 2018 1 A product designer is creating a poster. (a) The designer creates a 6-colour bitmap image for the poster as shown. Each colour is represented by a letter, for example, R = red, B = blue. R R P P P G B R R P G G B W B B O O B W W P P O B B R P G O B R R P G O (i) State the minimum number of bits needed to represent each pixel in the image in part (a). …[1] (ii) Calculate the minimum file size of the image shown in part (a). Show your working. Working … … … File size … [3] (b) (i) The designer takes a photograph to put on the poster. The photograph has a resolution of 50 000 pixels by 50 000 pixels. The colours are represented using 4 bytes per pixel. Estimate the file size of the photograph in gigabytes. Show your working. Working … … … … Estimated file size … [4]

3 9608/13/O/N/18 © UCLES 2018 [Turn over (ii) The photograph needs to be sent by email but the file size is too big. It needs to be compressed. The table lists several methods of making an image file size smaller. Tick (✓) one box on each row to indicate whether each method is lossy or lossless. Compression method Lossy Lossless Cropping the image Reducing the resolution of the image Using run-length encoding (RLE) Reducing the colour depth of the image [4] (c) Explain how run-length encoding would compress the image in part (a). … … … … … …[3]

4 9608/13/O/N/18 © UCLES 2018 2 The following table shows assembly language instructions for a processor which has one general purpose register, the Accumulator (ACC) and an Index Register (IX). Instruction Explanation Op code Operand LDD <address> Direct addressing. Load the contents of the location at the given address to ACC. LDX <address> Indexed addressing. Form the address from <address> + the contents of the Index Register. Copy the contents of this calculated address to ACC. LDR #n Immediate addressing. Load the number n to IX. STO <address> Store contents of ACC at the given address. ADD <address> Add the contents of the given address to ACC. INC <register> Add 1 to the contents of the register (ACC or IX). DEC <register> Subtract 1 from the contents of the register (ACC or IX). CMP <address> Compare contents of ACC with contents of <address>. JPE <address> Following compare instruction, jump to <address> if the compare was True. JPN <address> Following compare instruction, jump to <address> if the compare was False. JMP <address> Jump to the given address. OUT Output to the screen the character whose ASCII value is stored in ACC. END Return control to the operating system. (a) State what is meant by relative addressing and indexed addressing. Relative addressing … … … Indexed addressing … … … [2]

5 9608/13/O/N/18 © UCLES 2018 [Turn over (b) The current contents of a general purpose register (X) are: X 1 1 1 1 0 0 1 0 (i) The contents of X represent an unsigned binary integer. Convert the value in X into denary. …[1] (ii) The contents of X represent an unsigned binary integer. Convert the value in X into hexadecimal. …[1] (iii) The contents of X represent a two’s complement binary integer. Convert the value in X into denary. …[1] (iv) Show the result on the general purpose register (X) after the following instruction is run. INC X [1]

6 9608/13/O/N/18 © UCLES 2018 (c) The current contents of the main memory, Index Register (IX) and selected values from the ASCII character set are provided with a copy of the instruction set. Instruction set Instruction Explanation Op code Operand LDD <address> Direct addressing. Load the contents of the location at the given address to ACC. LDX <address> Indexed addressing. Form the address from <address> + the contents of the Index Register. Copy the contents of this calculated address to ACC. LDR #n Immediate addressing. Load the number n to IX. STO <address> Store contents of ACC at the given address. ADD <address> Add the contents of the given address to ACC. INC <register> Add 1 to the contents of the register (ACC or IX). DEC <register> Subtract 1 from the contents of the register (ACC or IX). CMP <address> Compare contents of ACC with contents of <address>. JPE <address> Following a compare instruction, jump to <address> if the compare was True. JPN <address> Following a compare instruction, jump to <address> if the compare was False. JMP <address> Jump to the given address. OUT Output to the screen the character whose ASCII value is stored in ACC. END Return control to the operating system. Address Instruction 20 LDD 96 21 CMP 97 22 JPE 32 23 LDX 86 24 CMP 98 25 JPN 27 26 OUT 27 LDD 96 28 INC ACC 29 STO 96 30 INC IX 31 JMP 21 32 END … 93 453 94 453 95 452 96 8 97 10 98 453 IX 8 ASCII code table (selected codes only) ASCII code Character 450 < 451 > 452 = 453 & 454 ( 455 )

7 9608/13/O/N/18 © UCLES 2018 [Turn over Complete the trace table for the given assembly language program. Instruction address ACC Memory address IX OUTPUT 93 94 95 96 97 98 453 453 452 8 10 453 8 20 [7]

8 9608/13/O/N/18 © UCLES 2018 3 This question presents three scenarios. Tick (✓) one box for each scenario to indicate whether you think the person’s behaviour is ethical or unethical. Justify your choice. (a) Mason is using his work computer to book a holiday whilst at work. Ethical Unethical Justification … … … …[2] (b) Ethan is supervising a trainee. The trainee asks Ethan for a reference for another job. Ethan does not want to lose the trainee, so refuses to give him a reference. Ethical Unethical Justification … … … …[2] (c) Margarita finds that one of her team members has produced some inventive code. She presents this to her manager, praising the individual by name. Ethical Unethical Justification … … … …[2]

9 9608/13/O/N/18 © UCLES 2018 [Turn over 4 Ava needs to view a website and she knows the Uniform Resource Locator (URL). (a) Complete the series of steps that take place. Write the letter of the appropriate statement in each space. A DNS finds corresponding IP B DNS looks up URL in table C Ava types the URL into a web browser 1 … 2 Web browser sends URL to Domain Name Service (DNS) 3 … 4 … 5 DNS returns IP address to web browser [2] (b) (i) An IPv4 address has been entered as 12.258.3 Give two reasons why this IP address is invalid. 1 … … 2 … … [2] (ii) An IPv6 address has been entered as 15EF:5L63::2014:BB::60AA Give two reasons why this IP address is invalid. 1 … … 2 … … [2]

10 9608/13/O/N/18 © UCLES 2018 (c) The table shows four descriptions of IP addresses. Tick (✓) one box in each row to identify whether each description applies to a public or private IP address. Description Public Private The address can be reached over the Internet. The address is more secure. The address can only be accessed through the same LAN. The address can be duplicated in different networks. [4]

11 9608/13/O/N/18 © UCLES 2018 [Turn over 5 Arnold is a software developer. He has created a computer game for people to download over the Internet. Arnold is considering releasing the game as a piece of commercial software. (a) (i) Describe what is meant by a commercial licence. … … … …[2] (ii) Name and describe one other type of licence that Arnold can consider using. Licence type … Description … … … … [3] (b) Users need to enter their name and email address to create an account. The information is stored in a database on Arnold’s computer. Give three ways that Arnold can ensure users’ details are kept secure. 1 … 2 … 3 … [3]

12 9608/13/O/N/18 © UCLES 2018 6 The fetch-execute (FE) cycle uses special purpose registers. (a) The stages in the FE cycle are shown in register transfer notation. MAR […] PC PC + 1 … [ [MAR] ] … [MDR] (i) The steps shown in part (a) are incomplete. Write the missing register names in the spaces in part (a). [3] (ii) The third instruction [ [MAR] ] has double brackets. State the purpose of the double brackets. … …[1] (b) One stage of the FE cycle includes checking for interrupts. State what is meant by an interrupt. … … … …[2] (c) There are two types of RAM: dynamic RAM (DRAM) and static RAM (SRAM). The following table shows five statements about DRAM and SRAM. Tick (✓) one box in each row to indicate whether the statement applies to DRAM or SRAM. Statement DRAM SRAM Does not need to be refreshed as the circuit holds the data while the power supply is on Mainly used in cache memory of processors where speed is important Has less complex circuitry Requires higher power consumption under low levels of access, which is significant when used in battery-powered devices Requires data to be refreshed occasionally so it retains the data [5]

13 9608/13/O/N/18 © UCLES 2018 [Turn over 7 The network manager of a Local Area Network (LAN) has replaced the Ethernet cables with a wireless network. (a) Give three benefits of a wireless network compared to a wired network. 1 … … 2 … … 3 … … [3] (b) Give one drawback of a wireless network compared to a wired network. … …[1]

14 9608/13/O/N/18 © UCLES 2018 8 (a) Draw a logic circuit to represent the logic expression: X = (A XOR B) OR (NOT(C AND A)) A B C X [4] (b) Complete the truth table for the logic expression in part (a). A B C Working space X 0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1 [4]

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16 9608/13/O/N/18 © UCLES 2018 Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity. To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge International Examinations Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cie.org.uk after the live examination series. Cambridge International Examinations is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge. BLANK PAGE

This document consists of 10 printed pages. © UCLES 2018 [Turn over Cambridge Assessment International Education Cambridge International Advanced Subsidiary and Advanced Level COMPUTER SCIENCE 9608/13 Paper 1 Written Paper October/November 2018 MARK SCHEME Maximum Mark: 75 Published This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners’ meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge International will not enter into discussions about these mark schemes. Cambridge International is publishing the mark schemes for the October/November 2018 series for most Cambridge IGCSE™, Cambridge International A and AS Level components and some Cambridge O Level components.

9608/13 Cambridge International AS/A Level – Mark Scheme PUBLISHED October/November 2018 © UCLES 2018 Page 2 of 10 Generic Marking Principles These general marking principles must be applied by all examiners when marking candidate answers. They should be applied alongside the specific content of the mark scheme or generic level descriptors for a question. Each question paper and mark scheme will also comply with these marking principles. GENERIC MARKING PRINCIPLE 1: Marks must be awarded in line with: • the specific content of the mark scheme or the generic level descriptors for the question • the specific skills defined in the mark scheme or in the generic level descriptors for the question • the standard of response required by a candidate as exemplified by the standardisation scripts. GENERIC MARKING PRINCIPLE 2: Marks awarded are always whole marks (not half marks, or other fractions). GENERIC MARKING PRINCIPLE 3: Marks must be awarded positively: • marks are awarded for correct/valid answers, as defined in the mark scheme. However, credit is given for valid answers which go beyond the scope of the syllabus and mark scheme, referring to your Team Leader as appropriate • marks are awarded when candidates clearly demonstrate what they know and can do • marks are not deducted for errors • marks are not deducted for omissions • answers should only be judged on the quality of spelling, punctuation and grammar when these features are specifically assessed by the question as indicated by the mark scheme. The meaning, however, should be unambiguous. GENERIC MARKING PRINCIPLE 4: Rules must be applied consistently e.g. in situations where candidates have not followed instructions or in the application of generic level descriptors. GENERIC MARKING PRINCIPLE 5: Marks should be awarded using the full range of marks defined in the mark scheme for the question (however; the use of the full mark range may be limited according to the quality of the candidate responses seen). GENERIC MARKING PRINCIPLE 6: Marks awarded are based solely on the requirements as defined in the mark scheme. Marks should not be awarded with grade thresholds or grade descriptors in mind.

9608/13 Cambridge International AS/A Level – Mark Scheme PUBLISHED October/November 2018 © UCLES 2018 Page 3 of 10 Question Answer Marks 1(a)(i) 3 1 1(a)(ii) 1 mark per bullet point • Number of pixels: 6 × 6 = 36 • Number of bits: Number of pixels (36) × 3 • 108 bits / 13.5 bytes 3 1(b)(i) 1 mark per bullet point • Number of pixels: 50 000 × 50 000 = 2 500 000 000 • Number of bytes: Number of pixels (2 500 000 000) × 4 // 10 000 000 000 // Number of bits: Number of pixels (2 500 000 000) × 32 // 80 000 000 000 • Conversion to gigabytes • 10 GB / 9.3 GB 4 1(b)(ii) 1 mark for correct tick in each row. Compression method Lossy Lossless Cropping the image 9 Reducing the resolution of the image 9 Using run-length encoding (RLE) 9 Reducing the colour depth of the image 9 4 1(c) 1 mark per bullet point to max 3 • Looks for runs of consecutive pixel of the same colour • Stores the colour value once and the number of times it occurs • Lossless method of compression • Reference to the given image in context 3 Question Answer Marks 2(a) 1 mark per bullet point Relative addressing: • A number (the offset) is added to the base address to give the actual address Indexed addressing: • The contents of the index register are added to operand to give the actual address 2 2(b)(i) 242 1

9608/13 Cambridge International AS/A Level – Mark Scheme PUBLISHED October/November 2018 © UCLES 2018 Page 4 of 10 Question Answer Marks 2(b)(ii) F2 1 2(b)(iii) –14 1 2(b)(iv) 1 1 1 1 0 0 1 1 1 2(c) 1 mark per bullet point • Loading 8 (instruction 20) • Comparison and loading 453 (instructions 21–23) • Outputting & (instruction 26) • Loading, incrementing and storing in 96 (instructions 27–29) • Incrementing Index Register (instruction 30) • Jumping and loading 452 (instruction 23) • Jumping, loading, incrementing, storing in 96, incrementing IX and end (instructions 24–32) 7

9608/13 Cambridge International AS/A Level – Mark Scheme PUBLISHED October/November 2018 © UCLES 2018 Page 5 of 10 Instruction address ACC Memory address IX OUTPUT 93 94 95 96 97 98 453 453 452 8 10 453 8 20 8 21 22 23 453 24 25 26 & 27 8 28 9 29 9 30 9 31 21 22 23 452 24 25 27 9 28 10 29 10 30 10 31 21 22 32

9608/13 Cambridge International AS/A Level – Mark Scheme PUBLISHED October/November 2018 © UCLES 2018 Page 6 of 10 Question Answer Marks 3(a) Either Ethical • He is booking the holiday in his own time / lunchtime // he is self-employed • He has been given permission • Reference to IEEE in context Or Unethical • Should not use company computer for personal use • Should be working whilst at work • Reference to IEEE in context 2 3(b) Unethical: Max 2 marks from • Company will get a bad reputation • Should be supporting his colleague • Reference to IEEE in context 2 3(c) Either Ethical • She is supporting her colleague • Working in the best interests of the company • Reference to IEEE in context Or Unethical • Praising one team member instead of the whole team • Others in the team may also have contributed, so she is not being supportive of the whole team • Reference to IEEE in context 2 Question Answer Marks 4(a) 1 mark for 1 letter in correct space 2 marks for all 3 letters in correct places 1 C 2 URL goes to Domain Name Service (DNS) 3 B 4 A 5 DNS returns IP address to client 2 4(b)(i) 1 mark per bullet point • 258 is too large/largest individual numbers is 255 • 4 numbers needed/1 number missing/only 3 groups of numbers given 2

9608/13 Cambridge International AS/A Level – Mark Scheme PUBLISHED October/November 2018 © UCLES 2018 Page 7 of 10 Question Answer Marks 4(b)(ii) 1 mark per bullet point • L not a valid hexadecimal number • Only one double colon is allowed 2 4(c) 1 mark per row Description Public Private The address can be reached over the Internet. 9 The address is more secure. 9 The address can only be accessed through the same LAN. 9 The address can be duplicated in different networks. 9 4 Question Answer Marks 5(a)(i) 1 mark per bullet point, max 2 • Restricted use • Source code not provided // source code protected • Anyone can purchase/download if agree to the terms • Limited number of installations allowed // Software key needed to install 2 5(a)(ii) 1 mark for name and 2 marks for description Either Open Source • The source code is released with the program • Users can change / edit the source code to enhance the game • Users can re-release the game under the same terms // the game might spread more easily Or Shareware • Users get free trial or limited access for set time • Users do not have access to the source code // source code may not be edited • At end of trial period, users may have to pay or register to continue using the game // Can get people ‘hooked’ and then charge a fee Or Freeware • There is no fee for the game • The game could be copyrighted • Modification, re-distribution or reverse engineering of the game without permission is prohibited 3

9608/13 Cambridge International AS/A Level – Mark Scheme PUBLISHED October/November 2018 © UCLES 2018 Page 8 of 10 Question Answer Marks 5(b) 1 mark per bullet point, max 3 • Firewall / proxy • Encryption • Username and Password • Physical security • Biometric authentication // by example • Two-step authentication // by example • Anti-malware 3 Question Answer Marks 6(a)(i) MAR ← [PC] PC ← PC + 1 MDR ← [ [MAR] ] CIR ← [MDR] 3 6(a)(ii) 1 mark from: • The contents of the MAR is an address, it is the contents of that address which is transferred to MDR • The contents of the address pointed to by the MAR is transferred to the MDR 1 6(b) 1 mark per bullet point to max 2 • A signal from a source / device • Telling the processor its attention is needed 2 6(c) 1 mark per row Statement DRAM SRAM Does not need to be refreshed as the circuit holds the data while the power supply is on 3 Mainly used in cache memory of processors where speed is important 3 Has less complex circuitry 3 Requires higher power consumption under low levels of access, which is significant when used in battery-powered devices 3 Requires data to be refreshed occasionally so it retains the data 3 5

9608/13 Cambridge International AS/A Level – Mark Scheme PUBLISHED October/November 2018 © UCLES 2018 Page 9 of 10 Question Answer Marks 7(a) 1 mark per benefit to max 3 • Devices can be more mobile as they do not have to be connected to cable • Easier to set up // no cables need to be installed • Add additional devices is easier • Many different types of device can be connected at the same time 3 7(b) 1 mark for a drawback from the following: • Easier to hack • Interference • Signal degrades quickly 1 Question Answer Marks 8(a) 1 mark for each logic gate with the correct inputs 4

9608/13 Cambridge International AS/A Level – Mark Scheme PUBLISHED October/November 2018 © UCLES 2018 Page 10 of 10 Question Answer Marks 8(b) One mark for each correct pair of lines A B C Working Space X 0 0 0 1 0 0 1 1 0 1 0 1 0 1 1 1 1 0 0 1 1 0 1 1 1 1 0 1 1 1 1 0 4