Cambridge A Level Computer Science 9618 — 2021 Oct/Nov Paper 1 · Variant 3

This document has 16 pages. Any blank pages are indicated. DC (RW/FC) 206387/2 © UCLES 2021 [Turn over * 0 3 9 2 4 1 0 2 6 3 * COMPUTER SCIENCE 9618/13 Paper 1 Theory Fundamentals October/November 2021 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. Cambridge International AS & A Level

2 9618/13/O/N/21 © UCLES 2021 1 (a) Draw one line from each binary value to its equivalent (same) value on the right. 1 kibibyte 1 gigabyte 1 byte 1 kilobyte 1 gibibyte 1 megabyte 1 mebibyte 8 bits 8000 bits 1000 kilobytes 1024 mebibytes 8192 bits Binary value [5] (b) (i) Perform the following binary addition. Show your working. 10101010 + 00110111 [2] (ii) State how an overflow can occur when adding two binary integers. … … [1] (c) Convert the hexadecimal value F0 into denary. … … [1]

3 9618/13/O/N/21 © UCLES 2021 [Turn over 2 Xanthe wants to maintain the integrity and security of data stored on her computer. (a) Explain the difference between data security and data integrity. … … … … [2] (b) Xanthe uses both data validation and data verification when entering data on her computer. (i) Describe how data validation helps to protect the integrity of the data. Give an example in your answer. Description … … … Example … [2] (ii) Describe how data verification helps to protect the integrity of the data. Give an example in your answer. Description … … … Example … [2] (c) Two malware threats are spyware and viruses. Give two similarities and one difference between spyware and a virus. Similarity 1 … … Similarity 2 … … Difference … … [3]

4 9618/13/O/N/21 © UCLES 2021 3 A logic circuit is shown: A B C X (a) Write the logic expression for the logic circuit. … … [3] (b) Complete the truth table for the given 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 [2]

5 9618/13/O/N/21 © UCLES 2021 [Turn over (c) Identify one logic gate not used in the given logic circuit. Draw the symbol for the logic gate and complete its truth table. Logic gate: ……………………………… Symbol: Truth table: A B Output 0 0 0 1 1 0 1 1 [3]

6 9618/13/O/N/21 © UCLES 2021 4 Francis is starting his first job as a software developer for a multinational company. (a) Francis has been advised to join a professional ethical body. Describe the benefits to Francis of joining a professional ethical body. … … … … … … [3] (b) Francis is shown the software he will be working on. He is unfamiliar with the Integrated Development Environment (IDE) he is required to use. (i) Describe the ways in which Francis can act ethically in this situation. … … … … [2] (ii) A typical IDE provides debugging tools to support the testing of a program. Identify three other tools or features found in a typical IDE to support the writing of the program. 1 … 2 … 3 … [3] (c) Francis is part of a team writing a program. He finds an error in part of the program that has already been tested. He decides not to tell anyone because he is worried about the consequences. Explain the reasons why Francis acted unethically in this situation. … … … … [2]

7 9618/13/O/N/21 © UCLES 2021 [Turn over (d) Francis’s team use language translators. Complete the descriptions of language translators by writing the missing words. … are usually used when a high‑level language program is complete. They translate all the code at the same time and then run the program. They produce … files that can be run without the source code. … translate one line of a high‑level language program at a time, and then run that line of code. They are most useful while developing the programs because errors can be corrected and then the program continues from that line. Assemblers are used to translate assembly code into … . [4]

8 9618/13/O/N/21 © UCLES 2021 5 Javier owns many shops that sell cars. He employs several managers who are each in charge of one or more shops. He uses the relational database CARS to store the data about his business. Part of the database is shown: SHOP(ShopID, ManagerID, Address, Town, TelephoneNumber) MANAGER(ManagerID, FirstName, LastName, DateOfBirth, Wage) CAR(RegistrationNumber, Make, Model, NumberOfMiles, ShopID) (a) Tick () one box in each row to identify whether each field is a primary key or a foreign key. Table Field name Primary key Foreign key MANAGER ManagerID SHOP ManagerID CAR RegistrationNumber CAR ShopID [2] (b) Describe the ways in which access rights can be used to protect the data in Javier’s database from unauthorised access. … … … … … … [3]

9 9618/13/O/N/21 © UCLES 2021 [Turn over (c) Javier uses Data Definition Language (DDL) and Data Manipulation Language (DML) statements in his database. (i) Complete the following DML statements to return the number of cars for sale in each shop. SELECT COUNT(…) FROM … … ShopID [3] (ii) Complete the DML statement to include the following car in the table CAR. Field Data RegistrationNumber 123AA Make Tiger Model Lioness NumberOfMiles 10500 ShopID 12BSTREET … … CAR … ("123AA","Tiger","Lioness",10500,"12BSTREET") [2]

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11 9618/13/O/N/21 © UCLES 2021 [Turn over 6 (a) There are two errors in the following register transfer notation for the fetch‑execute cycle. 1 MAR [PC] 2 PC [PC] − 1 3 MDR [MAR] 4 CIR [MDR] Complete the following table by: • identifying the line number of each error • describing the error • writing the correct statement. Line number Description of the error Correct statement [4]

12 9618/13/O/N/21 © UCLES 2021 (b) The following table shows part of the instruction set for a processor. The processor has one general purpose register, the Accumulator (ACC), and an Index Register (IX). Instruction Explanation Opcode Operand LDM #n Immediate addressing. Load the number n to ACC LDD <address> Direct addressing. Load the contents of the location at the given address to ACC STO <address> Store the contents of ACC at the given address 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> JPN <address> Following a compare instruction, jump to <address> if the compare was False JMP <address> Jump to the given address IN Key in a character and store its ASCII value in ACC OUT Output to the screen the character whose ASCII value is stored in ACC END Return control to the operating system XOR #n Bitwise XOR operation of the contents of ACC with the operand XOR <address> Bitwise XOR operation of the contents of ACC with the contents of <address> AND #n Bitwise AND operation of the contents of ACC with the operand AND <address> Bitwise AND operation of the contents of ACC with the contents of <address> OR #n Bitwise OR operation of the contents of ACC with the operand OR <address> Bitwise OR operation of the contents of ACC with the contents of <address> LSL #n Bits in ACC are shifted logically n places to the left. Zeros are introduced on the right hand end LSR #n Bits in ACC are shifted logically n places to the right. Zeros are introduced on the left hand end <address> can be an absolute or symbolic address # denotes a denary number, e.g. #123 B denotes a binary number, e.g. B01001101 The current contents of main memory are shown: Address Data 100 00001111 101 11110000 102 01010101 103 11111111 104 00000000

13 9618/13/O/N/21 © UCLES 2021 [Turn over Each row of the following table shows the current contents of ACC in binary and the instruction that will be performed on those contents. Complete the table by writing the new contents of the ACC after the execution of each instruction. Current contents of the ACC Instruction New contents of the ACC 11111111 OR 101 00000000 XOR #15 10101010 LSR #2 01010101 AND 104 [4]

14 9618/13/O/N/21 © UCLES 2021 7 Bobby is recording a sound file for his school project. (a) He repeats the recording of the sound several times, with a different sample rate each time. (i) Describe the reasons why the sound is closer to the original when a higher sample rate is used. … … … … [2] (ii) Describe the reasons why the sound file size increases when a higher sample rate is used. … … … … [2] (b) Bobby wants to email the sound file to his school email address. He compresses the file before sending the email. (i) Explain the reasons why Bobby compresses the sound file. … … … … [2] (ii) Bobby uses lossless compression. Describe how lossless compression can compress the sound file. … … … … [2]

15 9618/13/O/N/21 © UCLES 2021 8 A school is setting up a network within one of its buildings. (a) State whether the network will be a LAN (local area network) or a WAN (wide area network). Justify your choice. … … … … … … [3] (b) One classroom in the building has 30 computers. The computers need to be connected to the network. Each computer has a network interface card (NIC). Identify two possible devices that can be used to physically connect the 30 computers to the rest of the network. 1 … 2 … [2] (c) The school has several laptops. Each laptop has a Wireless Network Interface Card (WNIC). Describe the functions of a Wireless Network Interface Card. … … … … … … … … [4]

16 9618/13/O/N/21 © UCLES 2021 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 9 printed pages. © UCLES 2021 [Turn over Cambridge International AS & A Level COMPUTER SCIENCE 9618/13 Paper 1 Theory Fundamentals October/November 2021 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 2021 series for most Cambridge IGCSE™, Cambridge International A and AS Level components and some Cambridge O Level components.

9618/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2021 © UCLES 2021 Page 2 of 9 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.

9618/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2021 © UCLES 2021 Page 3 of 9 Question Answer Marks 1(a) 1 mark for each correct line 5 1(b)(i) 1 mark for answer 1 mark for working e.g. 1010 1010 0011 0111 1110 0001 1 1 1 1 1 1 2 1(b)(ii) The result is a larger number than can be stored in the given number of bits. // The result is greater than 255 1 1(c) 240 1 8 bits 1 byte 8000 bits 1 kibibyte 8192 bits 1 kilobyte 1000 kilobytes 1024 mebibytes 1 gibibyte 1 gigabyte 1 megabyte 1 mebibyte

9618/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2021 © UCLES 2021 Page 4 of 9 Question Answer Marks 2(a) 1 mark per bullet point • security is protecting data from loss / corruption • integrity is ensuring the consistency / accuracy of the data 2 2(b)(i) 1 mark per bullet point • validation checks that data is reasonable / sensible • example e.g. checking data is the right number / type of characters 2 2(b)(ii) 1 mark per bullet point • verification checks that data is the same as the original • by example e.g. double entry 2 2(c) 1 mark per similarity to max 2 • Both are pieces of malicious software • Both are downloaded / installed/run without the user's knowledge • Both can pretend to be / are embedded in other legitimate software when downloaded // both try to avoid the firewall • Both run in the background 1 mark for difference • Virus can damage computer data; spyware only records / accesses data • Virus does not send data out of the computer; spyware sends recorded data to third party • Virus replicates itself; spyware does not replicate itself 3 Question Answer Marks 3(a) 1 mark per bullet point • A AND B … • … XOR C … • … OR NOT B ((A AND B) XOR C) OR NOT B 3

9618/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2021 © UCLES 2021 Page 5 of 9 Question Answer Marks 3(b) 1 mark for each set of 4 rows (shaded) A B C Working space X 0 0 0 1 0 0 1 1 0 1 0 0 0 1 1 1 1 0 0 1 1 0 1 1 1 1 0 1 1 1 1 0 2 3(c) 1 mark for gate, 1 mark for matching symbol, 1 mark for matching truth table NOR A B OUTPUT 0 0 1 0 1 0 1 0 0 1 1 0 NAND A B OUTPUT 0 0 1 0 1 1 1 0 1 1 1 0 3

9618/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2021 © UCLES 2021 Page 6 of 9 Question Answer Marks 4(a) 1 mark per bullet point to max 3 e.g. • He has ethical guidelines to follow • … so clients/other staff know the standards being applied • … so he does not have to decide what is ethical it's written down • Clients / staff know he is reputable • … recognition of his skills / knowledge • … there may be a test / requirements for entry • They provide help and support • … for example if he needs legal advice • They run training courses • … to keep his skills up-to-date 3 4(b)(i) 1 mark per bullet point to max 2 e.g. • He can tell the manager he has not used it • … and how he will get up-to-date • He can perform his own research on how to use it • He can explain to the manager that he needs additional training • He can(ask the manager to book on a training course • He can ask for a mentor / to shadow someone • He can practice at home before starting 2 4(b)(ii) 1 mark for each correct tool e.g. • Colour coding // pretty printing • Auto-complete • Auto-correct • Context sensitive prompts • Expand and collapse code blocks 3 4(c) 1 mark per bullet point to max 2 e.g. • He didn’t act in best interest of product • … because the product might fail because he didn’t report the error • He didn’t act in best interest of client • … because if the product does not work then they have been let down because he didn't report the error • He didn’t act in the best interest of the profession • … he is letting his profession down because he didn't report the error • He didn’t act in best interest of the company • ... not correcting the error early could lead to later problems 2

9618/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2021 © UCLES 2021 Page 7 of 9 Question Answer Marks 4(d) 1 mark for each correctly completed term Compilers are usually used when a high-level language program is complete. They translate all the code at the same time and then run the program. They produce executable/.exe/object code files that can be run without the source code. Interpreters translate one line of a high-level language program at a time, and then run that line of code. They are most useful while developing the programs because errors can be corrected and then the program continues from that line. Assemblers are used to translate assembly code into binary/machine code. 4 Question Answer Marks 5(a) 1 mark for 2 or 3 correct ticks, 2 marks for 4 correct ticks Table Field name Primary Key (PK) Foreign Key (FK) MANAGER ManagerID  SHOP ManagerID  CAR RegistrationNumber  CAR ShopID  2 5(b) 1 mark per bullet point • Access rights give managers / himself access to different elements • … by having different accounts / logins • … which have different access rights e.g. read only // no access / read / write • Specific views can be assigned to himself and to the managers • … e.g. managers can only see the data for their own shop(s) 3 5(c)(i) 1 mark per correctly completed statement SELECT COUNT(RegistrationNumber) FROM CAR GROUP BY ShopID 3 5(c)(ii) 1 mark for each correct statement INSERT INTO CAR VALUES ("123AA","Tiger","Lioness",10500,"12BSTREET") 2

9618/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2021 © UCLES 2021 Page 8 of 9 Question Answer Marks 6(a) 1 mark for identification of line and description of error 1 mark for the correct statement Line number Description of the error Correct statement 2 Program Counter should be incremented, not decremented PC ← [PC] + 1 3 It should be the contents of the address in the MAR MDR ← [[MAR]] 4 6(b) 1 mark for each correct row Current contents of the ACC Instruction New contents of the ACC 11111111 OR 101 11111111 00000000 XOR #15 00001111 10101010 LSR #2 00101010 01010101 AND 104 00000000 4 Question Answer Marks 7(a)(i) 1 mark per bullet point • Smaller time gaps between the samples • Makes the digital sound wave more accurate • Smaller quantisation errors 2 7(a)(ii) 1 mark per bullet point • More samples/data are taken/recorded • … so more bits are stored altogether 2 7(b)(i) 1 mark per bullet point • Reduces the file size • Faster to transmit/download • Original file is too large for email storage/attachment 2 7(b)(ii) 1 mark per bullet point to max 2 e.g. • Reduce amplitude to only the range used • … limited amplitudes mean fewer bits per sample • Run-length-encoding • … Where consecutive sounds are the same record the binary value of the sound and number of times it repeats • Record the changes instead of the actual sounds 2

9618/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2021 © UCLES 2021 Page 9 of 9 Question Answer Marks 8(a) 1 mark per bullet point • LAN • Small geographical area • No leasing external infrastructure / transmission media // does not use internet to transmit within the building 3 8(b) 1 mark per item • router • switch • hub 2 8(c) 1 mark per bullet point to max 4 • Provide interface to wireless network • … as an antenna • Receives analogue radio waves • … convert them to digital / binary • Checks incoming transmissions for correct MAC / IP address • … ignore transmissions not intended for it • Encrypts / encodes the data • Decrypts / decodes the data • Takes digital/binary input and converts to analogue waves • … sends the radio waves via the antenna 4