Cambridge A Level Computer Science 9608 — 2020 Oct/Nov Paper 1 · Variant 3

Cambridge International AS & A Level This document has 16 pages. Blank pages are indicated. DC (JC/CT) 188578/2 © UCLES 2020 [Turn over * 1 0 7 9 3 9 2 7 5 2 * COMPUTER SCIENCE 9608/13 Paper 1 Theory Fundamentals October/November 2020 1 hour 30 minutes You must answer on the question paper. No additional materials are needed. INSTRUCTIONS ● Answer all questions. ● Use a black or dark blue pen. ● Write your name, centre number and candidate number in the boxes at the top of the page. ● Write your answer to each question in the space provided. ● Do not use an erasable pen or correction fluid. ● Do not write on any bar codes. ● You may use an HB pencil for any diagrams, graphs or rough working. ● Calculators must not be used in this paper. INFORMATION ● The total mark for this paper is 75. ● The number of marks for each question or part question is shown in brackets [ ]. ● No marks will be awarded for using brand names of software packages or hardware.

2 9608/13/O/N/20 © UCLES 2020 1 Identify the most appropriate utility program to use for each of the following tasks. Task Utility program Rearrange the data on a disk so that files are contiguous, and all free space is collected together Prepare a disk for initial use Reduce the size of a file Examine a disk to find any bad sectors [4] 2 Four terms about videos are given with six descriptions. Draw one line from each term relating to videos to its correct description. The number of images that are displayed per second The number of pixels per unit of measurement e.g. per inch Each frame is split into two fields: the first field contains only the odd lines, the second field contains the even lines Only the pixels that have changed are transmitted The complete frame is reproduced in each scan of the image The number of pixels in the image Description Progressive encoding Frame rate Interlaced encoding Image resolution Term [4]

3 9608/13/O/N/20 © UCLES 2020 [Turn over 3 Hannah is writing a computer program using a high-level language. She uses both a compiler and an interpreter. (a) Describe the ways in which Hannah will use an interpreter while writing the program. … … … … [2] (b) Explain the reasons why Hannah uses a compiler when she has finished writing the program. … … … … [2] (c) Some high-level languages are partially compiled and partially interpreted. Give one benefit and one drawback of using a language that is partially compiled and partially interpreted. Benefit … … Drawback … … [2]

4 9608/13/O/N/20 © UCLES 2020 4 A laptop on a home network connects to the Internet through a router. (a) The laptop has an IP address. (i) Give the reasons why the laptop has an IP address. … … … … [2] (ii) The laptop’s IP address is private. Give the reasons why the laptop does not have a public IP address. … … … … [2] (iii) The router has an IPv4 address. Give three differences between the format of an IPv4 address and an IPv6 address. 1 … … 2 … … 3 … … [3]

5 9608/13/O/N/20 © UCLES 2020 [Turn over (b) A Public Switched Telephone Network (PSTN) is one example of a communication system that can be used to support the Internet. Identify and describe two other communication systems that can be used to support the Internet. System 1 … Description … … System 2 … Description … … [4]

6 9608/13/O/N/20 © UCLES 2020 (c) A web page contains PHP code. (i) Complete the following table by writing a description of the function of each line of PHP code. PHP code Description echo "Hello World"; $number1 = 22; $newValue = $_GET["number"]; print "Hello " . $name . "<br>"; [4] (ii) PHP is a server-side scripting language. Give an example of a client-side scripting language. … … [1] (d) The laptop includes a parity bit in each byte it transmits. Explain how parity checks protect the integrity of the data. … … … … [2]

7 9608/13/O/N/20 © UCLES 2020 [Turn over 5 The fetch-execute cycle is used when a computer processor runs a program. (a) (i) Complete the table by writing the register transfer notation for each of the descriptions. Letter Description Register transfer notation A The Memory Address Register (MAR) stores an address. The contents of this stored address are copied to the Memory Data Register (MDR). B The contents of the Program Counter (PC) are copied to the Memory Address Register (MAR). C The contents of the Memory Data Register (MDR) are copied to the Current Instruction Register (CIR). D The contents of the Program Counter (PC) are incremented. [4] (ii) Write one of the letters A, B, C or D (from the table above) on each row (1 to 4), to show the correct order of the fetch-execute cycle. 1 … 2 … 3 … 4 … [2] (b) Buses are used to transfer data between various components of the computer system. Tick (✓) one or more boxes on each row to identify the bus(es) each statement describes. Statement Address bus Control bus Data bus Receives data from the MAR Carries an address or an instruction or a value Transmits timing signals to components Bidirectional [2]

8 9608/13/O/N/20 © UCLES 2020 (c) The following table shows assembly language instructions for a processor that has one general purpose register, the Accumulator (ACC). Instruction Explanation Op code Operand INV Input a denary value from the keyboard and store it in ACC. LDD <address> Direct addressing. Load the contents of the location at the given address to ACC. LDM #n Immediate addressing. Load the denary number n to ACC. LDI <address> Indirect addressing. The address to be used is at the given address. Load the contents of this second address to ACC. ADD <address> Add the contents of the given address to ACC. OUT Output to screen the character whose ASCII value is stored in ACC. INC <register> Add 1 to the contents of the register (ACC or IX). CMP <address> Compare the contents of ACC with the 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. STO <address> Store contents of ACC at the given address. END Return control to the operating system. (i) The assembly language instructions are grouped according to their function. Write one example of an op code from the table of instructions for each of the following groups. Arithmetic … Data movement … [2] (ii) The current contents of the main memory are: Address Instruction 500 INV 501 STO 901 502 INV 503 STO 900 504 ADD 902 505 STO 902 506 LDD 903 507 INC ACC 508 STO 903 509 CMP 901 510 JPN 502 511 END … 900 901 902 0 903 0

9 9608/13/O/N/20 © UCLES 2020 [Turn over Trace the program currently in memory using the following trace table when the values 2, 10 and 3 are input. The first instruction has been completed for you. Instruction address ACC Memory address 900 901 902 903 0 0 500 2 [6]

10 9608/13/O/N/20 © UCLES 2020 (d) The current contents of a general-purpose register X are: X 1 1 0 0 1 0 1 0 (i) The contents of X represent an unsigned binary integer. Convert the contents of X into denary. … [1] (ii) The contents of X represent a two’s complement binary integer. Convert the contents of X into denary. … [1] (iii) State why the binary number in X cannot represent a Binary Coded Decimal (BCD). … … [1]

11 9608/13/O/N/20 © UCLES 2020 [Turn over 6 Lara is managing a team of software developers who are writing a computer program. (a) Benedict is one of the developers. He is struggling to keep up with his workload. Describe the ways in which Lara can ethically support Benedict. … … … … [2] (b) Lara has identified that when a specific sequence of actions is performed in the program, a run-time error causes the program to crash. She has decided there is not enough time to debug the code because the client needs the system urgently, and there is a possibility that the client may never perform this sequence of actions. Explain the reasons why Lara is not acting ethically. … … … … [2] (c) The client wants to copyright the final program so that no one else can copy or amend it. (i) State the purpose of copyrighting the computer program. … … [1] (ii) Identify two software licences that would be appropriate for the program. Licence 1 … Licence 2 … [2] (iii) Identify one software licence that would not be appropriate for the program. Justify your choice. Software licence … Justification … … … [2]

12 9608/13/O/N/20 © UCLES 2020 7 Wilbur uses vector graphics to create a logo for his company. Wilbur Designs (a) Describe how the logo is represented and encoded by the computer. … … … … … … … … [4] (b) Wilbur scans a hand drawn image. The scanned image uses 8 bits to store the colour for each pixel. The image is 2048 pixels wide by 1024 pixels high. (i) Calculate an estimate of the file size of the scanned image. Give your answer rounded to the nearest MB. Show your working. … … … … Answer … MB [2]

13 9608/13/O/N/20 © UCLES 2020 [Turn over (ii) Wilbur wants to compress the scanned image before emailing it to his colleague. Describe one lossy compression technique that Wilbur can use to compress this image. … … … … … … [3]

14 9608/13/O/N/20 © UCLES 2020 8 Consider the following logic circuit. A B X C (a) Complete the truth table for the logic circuit. 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] (b) Identify one logic gate not used in the logic circuit shown. Complete the truth table for this logic gate with the inputs A and B. Logic gate … A B Output 0 0 0 1 1 0 1 1 [2]

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16 9608/13/O/N/20 © UCLES 2020 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 Assessment International Education Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cambridgeinternational.org after the live examination series. Cambridge Assessment International Education is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of the University of Cambridge Local Examinations Syndicate (UCLES), which itself is a department of the University of Cambridge. BLANK PAGE

This document consists of 10 printed pages. © UCLES 2020 [Turn over Cambridge International AS & A Level COMPUTER SCIENCE 9608/13 Paper 1 Written Paper October/November 2020 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 2020 series for most Cambridge IGCSE™, Cambridge International A and AS Level and Cambridge Pre-U components, and some Cambridge O Level components.

9608/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2020 © UCLES 2020 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 2020 © UCLES 2020 Page 3 of 10 Question Answer Marks 1 1 mark for each correct utility program Task Utility program Rearrange the data on a disk so that files are contiguous, and all free space is collected together Disk defragmenter Prepare a disk for initial use Disk formatter Reduce the size of a file File compression Examine the disk to find any bad sectors Disk contents analysis / repair 4 Question Answer Marks 2 1 mark for each correct line 4 Question Answer Marks 3(a) 1 mark per bullet point to max 2 • To run / test the incomplete program • To locate individual errors in the program because the interpreter stops • … and allows the programmer to correct errors in real-time • To change the program and see the effects of the changes in real-time 2 Progressive encoding Frame rate Interlaced encoding Image resolution The number of images that are displayed per second The number of pixels per unit of measurement e.g. per inch Each frame is split into two fields, the first field contains only the odd lines, the second field contains the even lines Only the pixels that have changed are transmitted The complete frame is reproduced in each scan of the image The number of pixels in the image

9608/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2020 © UCLES 2020 Page 4 of 10 Question Answer Marks 3(b) 1 mark per bullet point to max 2 • To run / test the program multiple times without re-compiling • To produce an executable file • … so that it can be distributed without the source code 2 3(c) 1 mark for a benefit, 1 mark for a drawback Benefit: • Programs may be interpreted on different platforms Drawback: • Intermediate code / program still needs to be interpreted on the user’s computer, which may run slowly • Extra CPU resources may be required 2 Question Answer Marks 4(a)(i) 1 mark per bullet point • To identify the laptop on the home network • To allow the router to send data to the laptop from the Internet / another device on the home network 2 4(a)(ii) 1 mark per bullet point to max 2 • The router has the public IP address for the home network • All data comes through the router • The laptop is not accessible / visible to the outside world • … to ensure security // to protect the laptop from external threats 2 4(a)(iii) 1 mark per bullet point to max 3 • IPv4 has 4 groups of digits, IPv6 has 8 groups of digits • In IPv4 each group is from 0-255, in IPv6 each group is from 0-65535 • IPv4 uses a full-stop between each group, IPv6 uses a colon between each group • IPv4 is 32-bit, IPv6 is 128-bit // IPv4 uses 4 bytes, IPv6 uses 16 bytes 3 4(b) 1 mark for identification, 1 mark for further description • Dedicated lines / leased line services • Connection that is only used for that business/organisation // permanent connection • Cell phone network • Send data to cell towers over mobile connection • Satellite • Send data to satellites in orbit 4

9608/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2020 © UCLES 2020 Page 5 of 10 Question Answer Marks 4(c)(i) 1 mark for each correct description PHP Code Description echo "Hello World"; Outputs the string Hello World to the browser $number1 = 22; Stores the number 22 in the variable $number1 $newValue = $ _ GET["number"]; Get the value assigned to number and store it in the variable $newValue print "Hello " . $name . "<br>"; Output Hello, followed by the value stored in the variable $name and then force a new line break 4 4(c)(ii) 1 mark for a correct answer • Javascript 1 4(d) 1 mark per bullet point to max 2 • Automatically checks for errors on receipt of data • Alerts if data has been received incorrectly // requests data to be re-sent • Provides a verification check on data 2

9608/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2020 © UCLES 2020 Page 6 of 10 Question Answer Marks 5(a)(i) 1 mark for each correct row Letter Action Register transfer notation A The Memory Address Register (MAR) stores an address. The contents of this stored address are copied to the Memory Data Register (MDR). MDR ← [[MAR]] B The contents of the Program Counter (PC) are copied to the Memory Address Register (MAR). MAR ← [PC] C The contents of the Memory Data Register (MDR) are copied to the Current Instruction Register (CIR). CIR ← [MDR] D The contents of the Program Counter (PC) are incremented. PC ← [PC] + 1 4 5(a)(ii) 1 mark for B, A, C in order 1 mark for D at any point after B 2 5(b) 1 mark for the first three rows correct 1 mark for the last row correct Statement Address bus Control bus Data bus Receives data from the MAR  Carries an address or an instruction or a value  Transmits timing signals to components  Bidirectional   2

9608/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2020 © UCLES 2020 Page 7 of 10 Question Answer Marks 5(c)(i) 1 mark for each correct example, ignore operand Arithmetic: • ADD // INC Data movement • STO // LDD // LDI // LDM 2 5(c)(ii) 1 mark for each correct shaded section Instruction address ACC Memory address 900 901 902 903 0 0 500 2 501 2 502 10 503 10 504 10 505 10 506 0 507 1 508 1 509 510 502 3 503 3 504 13 505 13 506 1 507 2 508 2 509 511 6 5(d)(i) 202 1 5(d)(ii) –54 1 5(d)(iii) Both nibbles are binary numbers representing denary numbers greater than 9 1

9608/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2020 © UCLES 2020 Page 8 of 10 Question Answer Marks 6(a) 1 mark for each valid point or appropriate expansion to max 2 e.g. • Reduce his workload // Review his work demands • Redistribute his work • Arrange a meeting with him • ... to discuss the reasons why he is struggling 2 6(b) 1 mark for each valid point or appropriate expansion to max 2 e.g. • Not acting in best interest of the client • ... The error could cause significant problems for the client if encountered • The product does not meet the highest possible standard • Not acting in the best interest of the development company • … if the error occurs, it could lead to repercussions for the development company 2 6(c)(i) 1 mark from • Protects the intellectual property • Allows legal action against anyone else who claims it as their own • Formally / Legally identify the client as the owner of the software 1 6(c)(ii) 1 mark for each correct licence • Commercial • Shareware 2 6(c)(iii) 1 mark for correctly identifying a licence, 1 mark for justification • Open Source // Free Software • Anyone can modify/copy the source code and re-distribute which is not what the client wants 2 Question Answer Marks 7(a) 1 mark per bullet point to max 4 • Each item is a drawing object • Properties of each drawing object are stored • … an example of a property e.g. the position/coordinates of each drawing object • … a second example of a property e.g. the line colour • Exact dimensions are not stored // a calculation for proportional size is stored • Objects are created using mathematical calculations 4

9608/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2020 © UCLES 2020 Page 9 of 10 Question Answer Marks 7(b)(i) 1 mark for working 1 mark for correct answer Working: 1024 × 2048 = 2 097 152 pixels = 2 097 152 bytes (8 bits per pixel) = 2 097 152 / 1024 = 2048 KB = 2048 / 1024 MB Answer: 2 MB 2 7(b)(ii) 1 mark for identification of method, max 2 for description for one method e.g. • Reduce the colour depth • … reduce the number of bits per colour • … each pixel has fewer bits • Reducing the resolution • … fewer pixels per unit measurement • … fewer pixels / binary numbers are stored 3 8(a) 1 mark for each pair of correct answers (shaded) A B C Working space X 0 0 0 1 0 0 1 0 0 1 0 1 0 1 1 1 1 0 0 0 1 0 1 0 1 1 0 1 1 1 1 0 4

9608/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2020 © UCLES 2020 Page 10 of 10 Question Answer Marks 8(b) 1 mark for correct name, 1 mark for corresponding truth table • NAND A B Output 0 0 1 0 1 1 1 0 1 1 1 0 • XOR A B Output 0 0 0 0 1 1 1 0 1 1 1 0 2