Cambridge A Level Computer Science 9608 — 2020 Oct/Nov Paper 1 · Variant 2

Cambridge International AS & A Level DC (KN) 188577/1 © UCLES 2020 [Turn over This document has 16 pages. Blank pages are indicated. * 2 6 8 9 5 3 3 7 0 3 * COMPUTER SCIENCE 9608/12 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 9608/12/O/N/20 © UCLES 2020 1 Different types of data can be represented in a computer system. (a) Numeric is one type of data. (i) Convert the following denary number into Binary Coded Decimal (BCD). 105 … [1] (ii) Convert the following two’s complement binary integer into denary. 10111111 … [1] (iii) Convert the following hexadecimal number into denary. AB … [1]

3 9608/12/O/N/20 © UCLES 2020 [Turn over (b) Character is another type of data. The following tables show part of the ASCII code character set. Character Denary value Character Denary value A 65 a 97 B 66 b 98 C 67 c 99 D 68 d 100 E 69 e 101 (i) Describe how the computer uses ASCII codes to represent characters. … … … … [2] (ii) Convert the following string into ASCII codes. Bed … … [1] (iii) Give the denary ASCII code for the following character. H … [1]

4 9608/12/O/N/20 © UCLES 2020 2 One method of compressing a file is run-length encoding (RLE). (a) Describe, using an example, how a text file is compressed using RLE. … … … … … … [3] (b) Explain why run-length encoding will sometimes increase the size of a text file. … … … … [2] 3 (a) Complete the following statements about CPU architecture by filling in the missing terms. The Von Neumann model for a computer system uses the … program concept. A program is a series of instructions that are saved in … . The processor … each instruction, … it and then … it. The processor uses several … to store the data and instructions from the program because they can be accessed faster than main memory. [6]

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6 9608/12/O/N/20 © UCLES 2020 (b) The following table shows assembly language instructions for a processor that has one general purpose register, the Accumulator (ACC). Instruction Explanation Op code Operand 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. STO <address> Store contents of ACC at the given address. ADD <address> Add the contents of the given address to ACC. CMP <address> Compare the contents of ACC with the contents of <address>. 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). 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. END Return control to the operating system. (i) The current contents of the main memory are: Address Instruction 50 LDD 80 51 ADD 80 52 STO 80 53 LDD 82 54 INC ACC 55 STO 82 56 CMP 81 57 JPN 50 58 LDD 80 59 OUT 60 END … 80 10 81 2 82 0 ASCII code table (Selected codes only) ASCII Code Character 38 & 39 ‘ 40 ( 41 ) 42 *

7 9608/12/O/N/20 © UCLES 2020 [Turn over Trace the program currently in memory using the following trace table. The first instruction has been completed for you. Instruction address ACC Memory address Output 80 81 82 10 2 0 50 10 [5]

8 9608/12/O/N/20 © UCLES 2020 (ii) Assembly language instructions can be put into groups. Tick (✓) one box in each column to identify the appropriate instruction group for each of the three assembly language instructions. Instruction group Assembly language instruction STO 80 JPN 50 INC ACC Input and output of data Data movement Arithmetic operations Unconditional and conditional jump instructions Compare instructions [3] 4 (a) Complete the truth table for the logic expression: X = ((A NOR B) AND (C XOR A)) OR B 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) Describe the difference between the operation of an AND gate and a NAND gate. … … … … [2]

9 9608/12/O/N/20 © UCLES 2020 [Turn over 5 A teacher uses a relational database, RESULTS, to store data about her students and their test results. (a) Describe the benefits to the teacher of using a relational database instead of a file-based approach. … … … … … … … … [4] (b) The teacher sets up the RESULTS database using a Database Management System (DBMS). (i) Explain the ways in which the developer interface of a DBMS will help the teacher set up the database. … … … … [2] (ii) The DBMS creates a data dictionary for the RESULTS database. Identify three items that will be included in the data dictionary. 1 … 2 … 3 … [3]

10 9608/12/O/N/20 © UCLES 2020 (c) The RESULTS database has the following structure: STUDENT(StudentID, FirstName, LastName, Class, TargetGrade) TEST(TestID, Topic, MaxMarks) STUDENT_TEST(StudentID, TestID, Mark) (i) Complete the following table by giving one example of each database term from the database RESULTS. Give both the field name and the corresponding table name. Database term Field name Table name Primary key Foreign key Attribute [3] (ii) Tick (✓) one box to identify whether the database RESULTS is in 1NF, 2NF or 3NF. Justify your choice. 1NF 2NF 3NF Justification: … … … … [3] (iii) Complete the Data Manipulation Language (DML) script to display the Student ID, mark and maximum marks for all tests with the topic of ‘Programming’. SELECT StudentID, Mark, … FROM STUDENT_TEST, … … Topic = "Programming" AND … = …; [5]

11 9608/12/O/N/20 © UCLES 2020 [Turn over (iv) The teacher wants to implement validation to make sure that all data entered into the database RESULTS are reasonable. Name three different methods of data validation that can be used in the RESULTS database. Describe how each method will limit the data that can be entered in this database. Method 1 … Description … … Method 2 … Description … … Method 3 … Description … … [6] (d) The teacher stores the database on the desktop computer in her classroom. (i) Explain why it is important to keep the database secure. … … … … [2] (ii) Explain the ways in which the teacher can use data backup and disk mirroring to limit the amount of data lost in the event of hardware failure. Data backup … … … … Disk mirroring … … … … [4]

12 9608/12/O/N/20 © UCLES 2020 6 Malika has started a new job as a trainee software engineer. (a) Malika’s manager has asked her to work with a senior software engineer for the first week. Explain the ways in which Malika’s manager has acted ethically. … … … … [2] (b) Malika researched the company and the programming languages used by the company before she started the job. Explain the ways in which Malika has acted ethically. … … … … [2] (c) Malika thinks that her colleagues do not like her, so she asks her manager for help. Describe the actions the manager could take to support Malika in an ethical way. … … … … [2]

13 9608/12/O/N/20 © UCLES 2020 7 A web server has a public IPv4 address. (a) Draw lines to link each characteristic to its appropriate IP address. Can use hexadecimal notation Characteristic IP address Each group of digits is a number between 0 and 65535 IPv4 IPv6 Consists of four groups of digits Uses double colons (::) The total length of the address is 32 bits [2] (b) IP addresses can be static or dynamic. Explain the reasons for the web server using a static instead of a dynamic IP address. … … … … … … [3]

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16 9608/12/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 11 printed pages. © UCLES 2020 [Turn over Cambridge International AS & A Level COMPUTER SCIENCE 9608/12 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.

9608/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2020 © UCLES 2020 Page 2 of 11 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.

9608/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2020 © UCLES 2020 Page 3 of 11 Question Answer Marks 1(a)(i) 0001 0000 0101 1 1(a)(ii) – 65 1 1(a)(iii) 171 1 1(b)(i) 1 mark per bullet point to max 2 • Each character has a unique character code • The binary value for each character in the string is stored in sequence • ASCII codes may be 7 or 8 bits long 2 1(b)(ii) 66 101 100 1 1(b)(iii) 72 1 Question Answer Marks 2(a) 1 mark per bullet point to max 2 for description • Instead of storing each repeated sequence of characters individually • … the character is stored and the number of consecutive occurrences 1 mark for using relevant example e.g. • instead of storing aaaa , store a4 3 2(b) 1 mark per bullet point to max 2 • Repeated sequences of characters rarely occur in text files // Most characters are used only once in any sequence • The character code and the fact that it is stored once will both be stored, which will use as much if not more space 2

9608/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2020 © UCLES 2020 Page 4 of 11 Question Answer Marks 3(a) 1 mark for each correct term Stored Memory Fetches Decodes Executes Registers The Von Neumann model uses the stored program concept. The program is a series of instructions that are saved in memory. The processor fetches each instruction, decodes it and then executes it. The processor uses several registers to store the data and instructions from the program because they can be accessed faster than main memory. 6

9608/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2020 © UCLES 2020 Page 5 of 11 Question Answer Marks 3(b)(i) 1 mark for each set of shaded rows Instruction address ACC Memory address Output 80 81 82 10 2 0 50 10 51 20 52 20 53 0 54 1 55 1 56 57 50 20 51 40 52 40 53 1 54 2 55 2 56 57 58 40 59 ( 60 5

9608/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2020 © UCLES 2020 Page 6 of 11 Question Answer Marks 3(b)(ii) 1 mark for each correct column. Instruction Group Assembly language instruction STO 80 JPN 50 INC ACC Input and output of data Data movement  Arithmetic operations  Unconditional and conditional jump instructions  Compare instructions 3 Question Answer Marks 4(a) 1 mark for each pair of answers A B C Working space X 0 0 0 0 0 0 1 1 0 1 0 1 0 1 1 1 1 0 0 0 1 0 1 0 1 1 0 1 1 1 1 1 4 4(b) 1 mark per bullet point to max 2 • AND is 1 only if both inputs are 1 • NAND is 0 only if both inputs are 1 // NAND is 1 whenever both inputs are not 1 2

9608/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2020 © UCLES 2020 Page 7 of 11 Question Answer Marks 5(a) 1 mark per bullet point to max 4 Max 3 if all generic, descriptions not related to benefits to the teacher. Max 3 for a list with no expansions • Linked tables can be set up • … the teacher can set up tables for her students and their results and link them by common attributes • Reduced data redundancy • … the teacher usually only needs to enter data once • Improved data integrity • … e.g. if they are searching for a student’s marks then all results for the student should be returned • Program-data dependence is overcome • … e.g. the teacher can add the results for additional tests without affecting the data already stored • Privacy is improved • … e.g. the teacher can prevent student access to the data (using views etc.) • Referential integrity can be enforced // Unwanted or accidental deletion of linked data is prevented • … e.g. A teacher cannot enter a mark for a student that does not exist // the teacher cannot accidently delete a student’s record while there are test results for that student • More complex searches and queries can be executed • … e.g. the teacher can set up a query to only return the test results for students who achieve below a certain mark 4 5(b)(i) 1 mark per bullet point to max 2 The teacher can ... • Set up forms for the input of student data • Add objects to a form to make data input easier, e.g. drop-down boxes • Design a report for the output of student marks • Add a menu to select options for different actions 2 5(b)(ii) 1 mark for each correct item to max 3 For example: • Table / entity names • Field / attribute names • Data types • Validation • Primary Keys 3

9608/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2020 © UCLES 2020 Page 8 of 11 Question Answer Marks 5(c)(i) 1 mark for each correct example Database term Field name Table name Primary key StudentID // TestID // StudentID and TestID STUDENT // TEST // STUDENT_TEST Foreign key StudentID // TestID STUDENT_TEST Attribute Any field from that table Any table 3 5(c)(ii) 1 mark for tick in correct box • It is in 3NF 1 mark per bullet point to max 2 for justification: • (It is in 1NF), there are no repeating groups of attributes // all attributes are atomic • (It is in 2NF), there are no partial dependencies • All fields are fully dependant on the PK // No transitive dependencies 3 5(c)(iii) 1 mark for each correct answer SELECT StudentID, Mark, MaxMarks / TEST.MaxMarks FROM STUDENT_TEST, TEST WHERE / WHERE Test.Topic = "Programming" AND TEST.TestID = STUDENT_TEST.TestID ; 5

9608/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2020 © UCLES 2020 Page 9 of 11 Question Answer Marks 5(c)(iv) 1 mark for correct name and 1 mark for corresponding description applied to RESULTS database. Max 2 per rule to max 3 rules The descriptions are examples only, there are many correct answers • Length check • Limit the target grade to 1 character • Range check • The mark for each test must be between 0 and MaxMarks • Existence check • The test topic must be in a pre-existing list • Presence check • A mark must be entered / not null • Format check • The data for a class must be one digit followed by one letter, e.g.3A • Type check • The maximum marks for a test must be an integer 6 5(d)(i) 1 mark per bullet point to max 2 • Stop unauthorised access // limit access to personal data about students • Prevent loss of data // avoid students’ test mark being deleted. • Prevent unauthorised changes to data // prevent students changing grades 2 5(d)(ii) 1 mark per bullet point to max 3 for each, max 4 in total Backup • A copy of the RESULTS database is made • ... at regular intervals // Sensible frequency of backups, e.g. daily, weekly etc. • ... and stored in a different location • So, in the event of data loss, (most of) the original data may be recovered. Disk mirroring • Data is written to different disks simultaneously • So, in the event of hardware failure, a second identical copy is immediately available. 4

9608/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2020 © UCLES 2020 Page 10 of 11 Question Answer Marks 6(a) 1 mark per bullet point to max 2 For example: • The manager is supporting her professional development • The manager is working in the best interest of his/her colleague (Malika) • This will ensure she is introduced to all aspects of the job • The manager is offering appropriate support 2 6(b) 1 mark per bullet point to max 2 For example: • She is acting in her own best interest • … by taking responsibility for her own professional development • She is acting in the best interests of her colleagues • … by ensuring she is up-to-date and does not need further training 2 6(c) 1 mark per bullet point to max 2 For example: • Discuss the problems with her • Discuss the concerns with her colleagues • Assign her a mentor who can reassure her • Team building exercises 2 7(a) 1 mark for correct lines from IPv4, 1 mark for correct lines from IPv6 Characteristic IP address 2 IPv4 IPv6 Can use hexadecimal notation Consists of four groups of digits Each group of digits is a number between 0 and 65535 Uses double colons (::) The total length of the address is 32 bits

9608/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2020 © UCLES 2020 Page 11 of 11 Question Answer Marks 7(b) 1 mark per bullet point to max 3 • Static IP does not change whereas a dynamic IP address does change • … the DNS does not need updating • … which might be delayed causing ‘address not found’ errors • The webserver may be accessed directly using just the IP address // the IP address is still held in cache memory 3