Cambridge A Level Computer Science 9608 — 2021 Oct/Nov Paper 1 · Variant 3

This document has 12 pages. Any blank pages are indicated. Cambridge International AS & A Level COMPUTER SCIENCE 9608/13 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. * 5 6 9 5 2 7 3 9 8 6 * DC (LK/FC) 205939/2 © UCLES 2021 [Turn over

2 9608/13/O/N/21 © UCLES 2021 1 (a) Convert the following two’s complement binary integer into denary. Show your working. 11001011 Working … … … … Answer … … [2] (b) Convert the following unsigned binary integer into hexadecimal. 10101101 … [1] (c) Convert the following denary integer to Binary Coded Decimal (BCD). 1753 … [1] (d) Give two examples of practical applications of BCD. 1 … … 2 … … [2]

3 9608/13/O/N/21 © UCLES 2021 [Turn over (e) An encryption routine replaces each character in a short message with a different character. For example, the following table shows how the routine encrypts the word ‘HELLO’ by adding 3 to the ASCII denary value of each character. Original character H E L L O ASCII denary value 72 69 76 76 79 ASCII denary value + 3 75 72 79 79 82 Encrypted character K H O O R The ASCII value of the character A is 65. Complete the table to show how the routine will encrypt the word ‘WANDS’. Original character W A N D S ASCII denary value ASCII denary value + 3 Encrypted character [2] 2 Daniel is creating a sound file for a school project. (a) Daniel records the sound using a sampling rate of 44.1 kHz and a sampling resolution of 16 bits. (i) State what is meant by a sampling rate of 44.1 kHz. … … [1] (ii) State what is meant by a sampling resolution of 16 bits. … … [1]

4 9608/13/O/N/21 © UCLES 2021 (b) Daniel needs to write a report about the sound he is using for his project. He will use a keyboard to write this report. Describe the basic internal operation of a keyboard. … … … … … … … … [4] 3 (a) Describe what is meant by a Public IP address and a Private IP address. Public IP address … … … … Private IP address … … … … [4] (b) Complete the following paragraph that describes the sequence of events when a user requests a page from a website. The user enters the Uniform Resource Locator (URL) into the address bar of the … . The domain name is taken from the URL and sent to a Domain Name Service (DNS). This stores … of domain names and their matching IP addresses. If it finds the domain name, it sends the IP address to the … . If it does not find the domain name, it sends the request to … . [4]

5 9608/13/O/N/21 © UCLES 2021 [Turn over 4 Draw the logic circuit for the logic expression: X = (A AND B) OR (NOT ((A AND C) AND (B OR C))) A B X C [6] 5 (a) Describe how the following registers are used in the fetch-execute (F-E) cycle: • Current Instruction Register (CIR) • Program Counter (PC) • Memory Data Register (MDR) • Memory Address Register (MAR). … … … … … … … … … … … … [5]

6 9608/13/O/N/21 © UCLES 2021 (b) Describe the roles carried out by the Arithmetic and Logic Unit (ALU) and the system clock. ALU … … System clock … … [2] (c) 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 Op code Operand LDM #n Immediate addressing. Load the number n to ACC CMP <address> Compare the contents of ACC with the contents of <address> ADD <address> Add the contents of the given address to the 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 STO <address> Store the contents of ACC at the given address END Return control to the operating system The instructions in the processor’s instruction set can be grouped according to their function. Identify one instruction group for each instruction in the following table. Instruction Instruction group LDM #12 ADD 21 STO 21 CMP 21 JPE 01 [5]

7 9608/13/O/N/21 © UCLES 2021 [Turn over (d) Some assemblers scan the assembly language program twice; these are referred to as two-pass assemblers. Complete these two sentences by writing the missing terms. In the first pass the … table is generated. In the second pass the program is converted into … code. [2] 6 Complete the table by writing the missing names and descriptions of utility software. Utility software Description Disk formatter … … … Reduces the size of the file Defragmenter … … … Making a copy of data in case of loss [4] 7 (a) Tick (3) one box in each row to identify whether each measure is an example of data verification or data validation. Measure Data verification Data validation Parity check Double entry Format check [2] (b) Identify one measure of data verification not given in part (a). … [1] (c) Identify one measure of data validation not given in part (a). … [1]

8 9608/13/O/N/21 © UCLES 2021 8 (a) Describe how run-length encoding (RLE) can be used to compress a single video frame. … … … … … … … … [4] (b) Identify two other methods of compressing a single video frame. 1 … … 2 … … [2] 9 A company uses a relational database. (a) The company stores data about its customers and their bank details. Explain the ways in which the database can be set up to only allow certain people to see the bank details. … … … … [2]

9 9608/13/O/N/21 © UCLES 2021 [Turn over (b) The database contains the following tables that store data about suppliers and stock. SUPPLIER(SupId, SupName, SupAddress, SupPhone, SupContactName) STOCK(StockId, SupId, StockName, StockImage, NumberInStock) (i) Write Data Manipulation Language (DML) statements to return the supplier name, phone number and contact name, and the number of items in stock for the item with the stock ID of D930. … … … … … … [4] (ii) The stock price needs to be included in the stock table. $10.55 and $299.99 are two examples of stock prices. Write Data Definition Language (DDL) statements to insert the attribute StockPrice into the table STOCK. … … … … [2]

10 9608/13/O/N/21 © UCLES 2021 (c) Three examples of items stored in the data dictionary of a relational database are: Item Purpose Field name to store the names of fields so they cannot be repeated in a table Primary key to uniquely identify each record in a table Validation rule to ensure that data entered is sensible Identify three other examples of items stored in a data dictionary and give the purpose of each. Item 1 … Purpose … … … Item 2 … Purpose … … … Item 3 … Purpose … … … [6]

11 9608/13/O/N/21 © UCLES 2021 (d) Draw one line from each database term to its matching description. Database term Description An attribute that could be a primary key but is not selected to be a primary key Logical schema An attribute in one table that is a primary key in another table Referential integrity The overview of a database structure Query processor An attribute or set of attributes that uniquely identifies each tuple Primary key Data between linked tables is consistent Secondary key Changing data to see what would happen in different scenarios The part of the DBMS that allows a user to search for data [5]

12 9608/13/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 9608/13 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.

9608/13 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.

9608/13 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 working 1 mark for correct answer 11001011 00110100 flip bits 00110101 add 1 32 + 16 + 4 + 1 Answer: −53 2 1(b) AD 1 1(c) 0001 0111 0101 0011 1 1(d) 1 mark per bullet point to max 2 Any scenario where a single digit needs to be displayed or transmitted • Electronic calculator displays • Date and time stored in BIOS of PCs or games consoles • Financial applications • Identification of latitude and longitude (e.g. cell towers) • Barcodes (MSI) 2 1(e) 1 mark for three correct columns 2 mark for all columns correct Original character W A N D S ASCII denary value 87 65 78 68 83 ASCII denary value + 3 90 68 81 71 86 Encrypted character Z D Q G V 2 Question Answer Marks 2(a)(i) 44.1 kHz = 44 100 samples/measurements per second/unit of time 1 2(a)(ii) 16 bits are used to store each sample 1

9608/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2021 © UCLES 2021 Page 4 of 9 Question Answer Marks 2(b) 1 mark per bullet point to max 4 • Uses switches and circuits to translate keystrokes into signals the computer can understand • The key matrix is a grid of circuits / three layers of plastic underneath the keys • Each circuit is broken beneath the key / middle layer contains holes • When key pressed, a circuit is made / completed and a signal is sent • The (keyboard) processor compares location of signal from key matrix to a character map stored on ROM • A character code for each key press is saved in a keyboard buffer 4 Question Answer Marks 3(a) 1 mark per bullet point to max 2 for each, max 4 • Public is assigned by an ISP • Public IP addresses can be accessed by anyone using the Internet • Public is used to get internet service • Public IP addresses must be unique throughout the Internet • Private is assigned by a router • Private IP addresses cannot be accessed by anyone using the Internet • Private is used to communicate within a network • Private can be duplicated in different networks // private addresses are unique only within the (local) network 4 3(b) 1 mark for each correct entry The user enters the Uniform Resource Locator (URL) into the address bar of the (web) browser. The domain name is taken from the URL and sent to a Domain Name Service (DNS). This stores an index/a list/a table of domain names and their matching IP addresses. If it finds the domain name, it sends the IP address to the (web) browser. If it does not find the domain name, it sends the request to a higher level/another DNS. 4

9608/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2021 © UCLES 2021 Page 5 of 9 Question Answer Marks 4 1 mark for each correct gate 6 Question Answer Marks 5(a) 1 mark per bullet point to max 5 • PC stores the address of the next instruction • The address in the PC is incremented • MAR points to the memory location to be accessed • MDR holds the data read from /to be written to... • …the address pointed to by the MAR • The instruction from the MDR is copied to the CIR • CIR holds the current instruction • …instruction in CIR is decoded • Decoded instruction in the CIR is executed by the processor 5 5(b) 1 mark per bullet point • The ALU is the part of the processor that carries out arithmetic operations and logic comparisons. • The system clock generates the timing signals // the system clock synchronises all the components on the motherboard 2 5(c) 1 mark for each correct group Instruction Instruction group LDM #12 Data movement ADD 21 Arithmetic Operations STO 21 Data Movement CMP 21 Compare Instructions JPE 01 Unconditional and Conditional Jump 5

9608/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2021 © UCLES 2021 Page 6 of 9 Question Answer Marks 5(d) 1 mark per bullet point • In the first pass the symbol table is generated. • In the second pass the program is converted into machine code. 2 Question Answer Marks 6 1 mark for each correct entry Utility software Description Disk formatter Initialise a disk for first use// Reformat a previously used disk// Partition a hard drive File compression Reduce the size of the file Defragmenter Find files that are not stored in contiguous blocks and move them together Backup Making a copy of data in case of loss 4 Question Answer Marks 7(a) 1 mark first two rows and 1 mark third row. Measure Data verification Data validation Parity check ✓ Double entry ✓ Format check ✓ 2 7(b) 1 mark from: • Checksum • Visual check • Echo check • ARQ 1

9608/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2021 © UCLES 2021 Page 7 of 9 Question Answer Marks 7(c) 1 mark from: • Presence check • Existence check // uniqueness check • Length check • Range/Limit check • Type/character check • Consistency check 1 Question Answer Marks 8(a) 1 mark per bullet point to max 4 • Frame is made up of pixels // is a single image • Each pixel has a binary value for its colour • Consecutive pixels with the same value/binary value/colour • …are stored as a single data value and a count • Accept a sensible example 4 8(b) 1 mark per bullet point to max 2 • Reduce colour/bit depth • Reduce image resolution 2 Question Answer Marks 9(a) 1 mark per bullet point to max 2 • Access rights • …manage the actions people can perform on parts of the database users have access to • Using views • …people can only see certain fields/tables • Put bank details in a different table • …limit access to that table 2 9(b)(i) 1 mark per correct bullet point • SELECT SupName, SupPhone, SupContactName, NumberInStock • FROM SUPPLIER, STOCK • WHERE StockId = 'D930' • AND SUPPLIER.SupId = STOCK.SupId; 4

9608/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2021 © UCLES 2021 Page 8 of 9 Question Answer Marks 9(b)(ii) 1 mark per bullet point • ALTER TABLE STOCK • ADD StockPrice REAL; 2 9(c) 1 mark per bullet point to max 6 For example: • Table names ... • ... to identify the tables • Foreign keys ... • ... to link tables // to create relationships between tables • Data types ... • ... to prevent the wrong data type being entered in a field • Passwords ... • ... to allow access only to authorised personnel • Access rights ... • ... for different levels of access 6

9608/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2021 © UCLES 2021 Page 9 of 9 Question Answer Marks 9(d) 1 mark for each correct line 5