Cambridge A Level Computer Science 9608 — 2015 Oct/Nov Paper 1 · Variant 1

This document consists of 12 printed pages. DC (CW/SG) 112120/2 © UCLES 2015 [Turn over Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level * 0 2 7 1 3 7 8 5 0 1 * COMPUTER SCIENCE 9608/11 Paper 1 Theory Fundamentals October/November 2015 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 9608/11/O/N/15 © UCLES 2015 1 (a) Explain the term bit streaming. … … … …[2] (b) A person watches a film streamed from a website on a tablet computer. (i) Give two benefits of using bit streaming for this purpose. 1 … … 2 … … [2] (ii) State two potential problems of using bit streaming for this purpose. 1 … … 2 … … [2] (c) Explain the terms on-demand bit streaming and real-time bit streaming. … … … … … … … … … …[4]

3 9608/11/O/N/15 © UCLES 2015 [Turn over 2 (a) Registers Processor ALU Control unit System clock Main memory B A C The diagram above shows a simplified form of processor architecture. Name the three buses labelled A, B and C. A … B … C … [3] (b) State the role of each of the following special purpose registers used in a typical processor. Program Counter … … Memory Data Register … … Current Instruction Register … … Memory Address Register … … [4]

4 9608/11/O/N/15 © UCLES 2015 3 (a) The table shows four statements about IP addresses. Tick (✓) to show which of the statements are true. Statement True (✓) The IP address consists of any number of digits separated by single dots (.) Each number in an IP address can range from 0 to 255 IP addresses are used to ensure that messages and data reach their correct destinations Public IP addresses are considered to be more secure than private IP addresses [2] (b) Consider the URL: http://cie.org.uk/computerscience.html (i) Give the meaning of the following parts of the URL. http … … … cie.org.uk … … … computerscience.html … … … [3] (ii) Sometimes the URL contains the characters %20 and ?. Describe the function of these characters. %20 … … ? … … [2]

5 9608/11/O/N/15 © UCLES 2015 [Turn over 4 Paul works part-time for a large software company. The company sells security software to a number of banks. He also runs his own software company that produces and sells computer games. Six statements about computer ethics are shown below. Draw lines to indicate whether each statement describes ethical or unethical behaviour. Statement To save time, Paul fakes the test results when testing the bank security software. Ethical Unethical Paul uses the software developed in his day job to help write some of the games software routines. To allow him to concentrate on his games software, Paul has frequently turned down job opportunities in his day job. To make the games software more realistic, Paul uses password protection code used in the bank security software. Because his work load is increasing, Paul is now using overseas companies to write some of the routines used in his games software. Paul carries out training on how to write games software in his spare time. [6]

6 9608/11/O/N/15 © UCLES 2015 5 A computer system in a control room is used to monitor earthquake activity. An earthquake zone has a number of sensors to detect seismic activity. The system detects when seismic activity is greater than 3 on the Richter Scale. Whenever this happens, a printer in the control room prints a report. (i) Identify the steps that are required in this monitoring system. … … … … … … …[4] (ii) When the system detects high activity, operators may need to respond rapidly. A printer is useful for hard copies, but may not be the best way to inform operators. Give a reason why. … …[1] (iii) Name an alternative output device for this monitoring system and give a reason for your choice. Output device … Reason for choice … … … [2]

7 9608/11/O/N/15 © UCLES 2015 [Turn over 6 A company operates a chemical plant, which has a number of processes. Local computers monitor these processes and collect data. The computers transfer these data to a central computer 50 km away. A telecommunications company (telco) provides cables. Engineers at the telco had to decide which type of cable to use. They considered the use of either copper cable or fibre optic cable. State two benefits of each type of cable. Each benefit must be clearly different. Benefits of copper cable 1 … … 2 … … Benefits of fibre optic cable 1 … … 2 … … [4]

8 9608/11/O/N/15 © UCLES 2015 7 (a) (i) Describe what is meant by a client-server model of networked computers. … … … …[2] (ii) Give two benefits of using the client-server model. 1 … … 2 … … [2] (b) The diagram shows a computer network with connection to the Internet. X client computer client computer file server mail server Internet Name the hardware device labelled X. …[1]

9 9608/11/O/N/15 © UCLES 2015 [Turn over (c) A web page offers a link for users to request another web page. The requested web page contains HTML code and JavaScript code. Put each statement in the correct sequence by writing the numbers 1 to 5 in the right-hand column. Statement Sequence number The requested web page is displayed on the client computer The user clicks on the hyperlink and the web page is requested from the web server The requested web page content is transmitted to the client computer The client computer processes the JavaScript code using the web browser software The web server locates the requested web page [5]

10 9608/11/O/N/15 © UCLES 2015 8 (a) Six computer graphics terms and seven descriptions are shown below. Draw a line to link each term to its correct description. Term Description Bitmap graphic Image file header Image resolution Pixel Screen resolution Vector graphic Measured in dots per inch (dpi); this value determines the amount of detail an image has Picture element Image made up of rows and columns of picture elements Image made up of drawing objects. The properties of each object determine its shape and appearance. Specifies the image size, number of colours, and other data needed to display the image data Number of samples taken per second to represent some event in a digital format Value quoted for a monitor specification, such as 1024 × 768. The larger the numbers, the more picture elements will be displayed. [6]

11 9608/11/O/N/15 © UCLES 2015 [Turn over (b) (i) A black and white image is 512 pixels by 256 pixels. Calculate the file size of this image in kilobytes (KB) (1 KB = 1024 bytes). Show your working. … … … … …[2] (ii) Give a reason why it is important to estimate the file size of an image. … … …[1] 9 (a) Give a brief description of each of the following terms: Validation … … … Verification … … …[2] (b) Data are to be transferred between two devices. Parity checks are carried out on the data. Explain what is meant by a parity check. Give an example to illustrate your answer. … … … … … … … …[4]

12 9608/11/O/N/15 © UCLES 2015 10 (a) Explain the term computer virus. … … … …[2] (b) A virus checker has been installed on a PC. Give two examples of when a virus checker should perform a check. 1 … … 2 … … [2] 11 A game program is written which can be either interpreted or compiled. The table below shows five statements about the use of interpreters and compilers. Tick (✓) to show whether the statement refers to an interpreter or to a compiler. Statement Interpreter Compiler This translator creates an executable file When this translator encounters a syntax error, game execution halts The translator analyses and checks each line just before executing it This translator will produce faster execution of the game program Use of this translator makes it more difficult for the user to modify the code of the game [5] 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.

® IGCSE is the registered trademark of Cambridge International Examinations. CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME for the October/November 2015 series 9608 COMPUTER SCIENCE 9608/11 Paper 1 (Written Paper), maximum raw mark 75 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 will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the October/November 2015 series for most Cambridge IGCSE®, Cambridge International A and AS Level components and some Cambridge O Level components.

Page 2 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9608 11 © Cambridge International Examinations 2015 1 (a) any two from: – sequence of digital signals / bits – over a communication path / Internet – transfer of data at high speed – requires fast broadband connection – requires some form of buffering – bits arrive in the same order as sent [2] (b) (i) any two from: – no need to wait for a whole file to be downloaded – no need to store large files on user’s computer – allows on demand playback – no specialist software is required for playback in browser [2] (ii) any two from: – video stops / hangs if very slow Internet / broadband speed low – video stops / hangs if inadequate buffering capacity – loss of Internet means can’t access films / files – may require specific software to run the files / films – viruses can be downloaded from the websites [2] (c) 2 marks for on-demand and 2 marks for real-time on-demand – digital video tape, analogue video tape, or digital files are converted to bit streaming – format for broadcasting on the net; this is known as encoding, these encoded streaming video files are then uploaded to a dedicated server – a link for the encoded video is placed on a web site – a user clicks on the link to download the encoded streaming video; the streamed video is – then broadcast to the user as and when they require it – can be paused / can go back and re-watch / fast-forward, etc. real-time – an event is captured live with a video camera – the video camera is connected to a computer – the video signal is converted to streaming media files (encoded) on the computer – the encoded feed is then uploaded from the computer to a dedicated streaming server via cable, DSL, or a high-speed internet connection – the server then sends the live images it to all users requesting it as real-time video streaming – cannot be paused etc. [4]

Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9608 11 © Cambridge International Examinations 2015 2 (a) A = control bus B = address bus C = data bus [3] (b) Program Counter – stores the address of next instruction to be executed Memory Data Register – stores the data in transit between memory and other registers // holds the instruction before it is passed to the CIR Current Instruction Register – stores the current instruction being executed Memory Address Register – stores the address of the memory location which is about to be accessed [4] 3 (a) Statement True (
) The IP address consists of any number of digits separated by single dots (.) Each number in an IP address can range from 0 to 255
IP addresses are used to ensure that messages and data reach their correct destinations
Public IP addresses are considered to be more secure than private IP addresses accept words TRUE or FALSE in right hand column 1 mark per tick, –1 mark for each wrong tick if more than 2 [2] (b) (i) http – enables browser to know what protocol is being used to access information in the domain cie.org.uk – cie.org.uk is the domain name computerscience.html – actual web page / file being viewed [3] (ii) %20 – because <space> not allowed in a URL, %20 is the coding for a space (32 in denary) ? – separates the URL from all parameters or variables [2]

Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9608 11 © Cambridge International Examinations 2015 4 1 mark for each correct line, two lines from one box is incorrect [6] To save time, Paul fakes the test results when testing the bank security software. Paul uses the software developed in his day job to help write some of the games software routines. To allow him to concentrate on his games software, Paul has frequently turned down job opportunities in his day job. To make the games software more realistic, Paul uses password protection code used in the bank security software. Because his workload is increasing, Paul is now using overseas companies to write some of the routines used in his games software. Paul carries out training on how to write games software in his spare time. Ethical Unethical

Page 5 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9608 11 © Cambridge International Examinations 2015 5 (i) any four from: – sensors send signals / data to a computer – data / signal converted to digital (using an ADC) – computer calculates the activity value based on sensor signal strength / data – if calculated value > 3, – determine location of sensor – build up a map of seismic activity – location and magnitude sent to printer – … via USB port / wireless link – monitoring is continuous [4] (ii) – output / hard copy not picked up in good time [1] (iii) 1 mark for name + 1 mark for reason for choice – speaker / buzzer / alarm bell – gives control room operators an audible warning – flashing lights – gives control room operators an visual warning – monitor – use of red / flashing colours on monitor gets the attention of operators [2] 6 any four points from (maximum 3 marks per type of cable): – fibre optic cables have greater bandwidth – fibre optic cables need less signal boosting // can transmit over longer distances – fibre optic cables have greater security (more difficult to “tap” into) – fibre optic cables are immune to electromagnetic and other effects – fibre optic cabling is lighter in weight (easier to install) – fibre optic cables consume less power – copper cabling is less expensive to install – copper cable is easier to install because it is more flexible – it is easier to make terminations using copper cabling – the expertise in use of copper cabling is more extensive – has been around for years … so very little is “unknown” about installations using this type of cabling [4]

Page 6 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9608 11 © Cambridge International Examinations 2015 7 (a) (i) – at least one computer used to “serve” … – … other computers are referred to as “clients” – server provides services / applications etc. … – … which may be requested by clients [2] (ii) any two from: – files and resources are centralised – creation of security / manage security – user needs user name and password to access network – centralised back-up – intranet capability – Internet monitoring – clients can be less powerful machines, therefore less expensive to buy – saving resources on server reduces the burden on the client [2] (b) router [1] (c) Statement Sequence number The requested web page is displayed on the client computer 5 The user clicks on the hyperlink and the web page is requested from the web server 1 The requested web page content is transmitted to the client computer 3 The client computer processes the JavaScript code using the web browser software 4 The web server locates the requested web page 2 [5]

Page 7 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9608 11 © Cambridge International Examinations 2015 8 (a) 1 mark for each correct line, two lines from one box is incorrect [6] Measured in dots per inch (dpi); this value determines the amount of detail an image has Picture element Image made up of rows and columns of picture elements Image made up of drawing objects; the properties of each object determine its shape and appearance Specifies the image size, number of colours, and other data needed to display an image Number of samples taken per second to represent some event in a digital format Value quoted for a monitor specification, such as 1024 × 768; the larger the numbers, the more picture elements will be displayed Bitmap graphic Image file header Image resolution Pixel Screen resolution Vector graphic

Page 8 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9608 11 © Cambridge International Examinations 2015 (b) (i) 1024 8 256 512 × × = 16 KB 1 mark for numerator + 1 mark for denominator [2] (ii) so it is possible to estimate how many images can be stored / to decide if it can be sent as an email attachment [1] 9 (a) One mark for validation, one mark for verification. validation – check whether data is reasonable / meets given criteria verification – method to ensure data which is copied / transferred is the same as the original – entering data twice and computer checks both sets of data – check entered data against original document / source [2] (b) any four from: – parity can be even or odd – parity check uses the number of 1s in a binary pattern – if there is an even / odd number of 1s, then the parity is even / odd – following transmission … – parity of each byte checked – a parity bit is used to make sure binary pattern has correct parity – example: 1 0 0 1 0 1 1 1 has parity bit set to 1 in MSB since system uses odd parity (original data: 0 0 1 0 1 1 1 which has four 1 bits) [4] 10 (a) any two from: – malicious code / software / program – that replicates / copies itself – can cause loss of data / corruption of data on the computer – can cause computer to “crash” / run slowly – can fill up hard disk with data [2] (b) any two from: – checks for boot sector viruses when machine is first turned on – when an external storage device is connected – checks a file / web page when it is accessed / downloaded [2]

Page 9 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9608 11 © Cambridge International Examinations 2015 11 Statement Interpreter Compiler This translator creates an executable file
When this translator encounters a syntax error, game execution will halt
The translator analyses and checks each line just before executing it
This translator will produce faster execution of the game program
Use of this translator makes it more difficult for the user to modify the code of the game supplied to the user
1 mark for each correct row [5]