Cambridge A Level Computer Science 9608 — 2015 Oct/Nov Paper 1 · Variant 2

This document consists of 14 printed pages and 2 blank pages. DC (ST/SW) 93611/2 © UCLES 2015 [Turn over Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level * 8 6 6 9 8 3 6 0 5 9 * COMPUTER SCIENCE 9608/12 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 9608/12/O/N/15 © UCLES 2015 1 (a) Give three differences between Dynamic RAM (DRAM) and Static RAM (SRAM). … … … … … …[3] (b) (i) Examples of primary and secondary storage devices include: • hard disk • DVD-RW • flash memory For each device, describe the type of media used. Hard disk … … DVD-RW … … Flash memory … …[3] (ii) Describe the internal operation of the following devices: DVD-RW … … DVD-RAM … …[2]

3 9608/12/O/N/15 © UCLES 2015 [Turn over 2 (a) Describe how a laser mouse operates. … … … … … …[3] (b) The following table shows a list of five statements which describe the stages when a page is printed using an inkjet printer. Put each statement in the correct sequence by writing the numbers 1 to 5 in the right-hand column. Statement Sequence number Paper feed stepper motor activated; sheet of paper fed from paper tray Printer driver translates data into a suitable format for the printer The print head moves across the page; ink is sprayed each time the print head pauses for a fraction of a second Paper feed stepper motor advances paper a fraction of a cm after each complete head pass Printer receives data from the computer and stores the data in the printer’s buffer [5]

4 9608/12/O/N/15 © UCLES 2015 3 A touch screen has three squares where a selection can be made: T S U (a) The x-coordinate of the centre of the three squares is held in three memory locations: Address Memory contents S 40 0000 1011 0100 T 41 0010 0101 0100 U 42 0100 0110 1100 (i) Give the hexadecimal value of the memory contents for U. … …[1] (ii) Convert the denary number 40 into binary. … …[1]

5 9608/12/O/N/15 © UCLES 2015 [Turn over (b) Bitmap graphics are used to represent squares S, T and U. These can be saved in a number of different image resolutions. (i) Give the number of bits required to store each pixel for a black and white bitmap. …[1] (ii) Identify how many bits are required to store each pixel for a 256-colour bitmap. Explain your answer. … … …[2] (c) Images can be compressed to reduce file size. (i) Describe how lossless compression techniques work. … … … …[2] (ii) Describe how lossy compression techniques work. … … … …[2]

6 9608/12/O/N/15 © UCLES 2015 4 (a) Sound can be represented digitally in a computer. Explain the terms sampling resolution and sampling rate. Sampling resolution … … … … Sampling rate … … … …[4] (b) The following information refers to a music track being recorded on a CD: • music is sampled 44 100 times per second • each sample is 16 bits • each track requires sampling for left and right speakers (i) Calculate the number of bytes required to store one second of sampled music. Show your working. … … … …[2] (ii) A particular track is four minutes long. Describe how you would calculate the number of megabytes required to store this track. … … … …[2]

7 9608/12/O/N/15 © UCLES 2015 [Turn over (c) When storing music tracks in a computer, the MP3 format is often used. This reduces file size by about 90%. Explain how the music quality is apparently retained. … … … … … …[3]

8 9608/12/O/N/15 © UCLES 2015 5 Bobby is a senior programmer at a software house which produces intruder detection software. He also runs his own software company which develops and sells various computer applications. The following table shows seven activities which Bobby carries out. Put a tick (✓) in the appropriate column to identify if the activity is ethical or unethical. Activity Ethical Unethical gives away passwords used in the intruder detection software uses source code developed at the software house for the software he develops for his own company insists that staff work to deadlines turns down training opportunities offered by his employer writes and sells software that reads confidential data from client computers fakes test results of safety-critical software has the software applications developed overseas for sale in his own country [7]

9 9608/12/O/N/15 © UCLES 2015 [Turn over 6 (a) A student wrote the following logic statement: X is 1 if (B is NOT 1 AND S is NOT 1) OR (P is NOT 1 AND S is 1) Draw a logic circuit to represent the above logic statement. B S X P [6] (b) Complete the truth table for this system. B S P 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]

10 9608/12/O/N/15 © UCLES 2015 7 (a) The string of characters, “BINARY CODE”, was transmitted using 11 bytes of data. An additional byte, called the parity byte, was also transmitted. Parity bytes can be used to identify exactly which bit has been transmitted incorrectly. The table shows bit patterns for all 12 bytes after transmission. Even parity was used and the first bit is the parity bit. character bit 1 bit 2 bit 3 bit 4 bit 5 bit 6 bit 7 bit 8 byte 1 B 0 1 0 0 0 0 1 0 byte 2 I 1 1 0 0 1 0 0 1 byte 3 N 0 1 0 0 1 1 1 0 byte 4 A 0 1 0 0 0 0 0 1 byte 5 R 1 1 0 1 0 0 1 0 byte 6 Y 0 1 1 1 1 0 0 1 byte 7 1 0 1 0 0 0 0 0 byte 8 C 1 1 0 0 0 0 1 1 byte 9 O 1 1 0 0 1 1 1 1 byte 10 D 0 1 0 0 0 1 0 0 byte 11 E 1 1 0 0 0 1 0 1 parity byte 0 0 1 0 0 0 1 0 (i) There is one error in the transmission. Indicate the byte number and bit number of the bit which has been incorrectly transmitted. Byte number … Bit number …[2] (ii) Explain your answer to part (i). … … … …[2]

11 9608/12/O/N/15 © UCLES 2015 [Turn over (b) Verification and validation can be applied during data entry. Describe what is meant by these terms. For each method, explain why it is needed. Verification … … … … Validation … … … …[4]

12 9608/12/O/N/15 © UCLES 2015 8 The table shows assembly language instructions for a processor which has one general purpose register – the Accumulator (ACC). Instruction Explanation Op code Operand LDD <address> Direct addressing. Load the contents of the given address to ACC LDX <address> Index addressing. Form the address from <address> + the contents of the index register. Copy the contents of this calculated address 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 the contents of ACC at the given address INC <register> Add 1 to contents of the register (ACC or IX) ADD <address> Add the contents of the given address to the ACC END Return control to the operating system The diagram shows the contents of the memory: 100 101 102 103 104 105 106 107 0 0 0 0 0 0 1 0 1 0 0 1 0 0 1 1 0 1 1 1 0 0 1 1 0 1 1 0 1 0 1 1 0 1 1 1 1 1 1 0 1 0 1 1 0 0 0 1 0 1 1 0 1 0 0 0 0 1 0 0 1 0 1 1 main memory 200 1 0 0 1 1 1 1 0 (a) (i) Show the contents of the Accumulator after execution of the instruction: LDD 102 Accumulator: [1]

13 9608/12/O/N/15 © UCLES 2015 [Turn over (ii) Show the contents of the Accumulator after execution of the instruction: LDX 101 Index register: 0 0 0 0 0 1 0 0 Accumulator: Explain how you arrived at your answer. … … … …[3] (iii) Show the contents of the Accumulator after execution of the instruction: LDI 103 Accumulator: Explain how you arrived at your answer. … … … … … …[4]

14 9608/12/O/N/15 © UCLES 2015 (b) Trace the assembly language program using the trace table. 800 LDD 810 801 INC 802 STO 812 803 LDD 811 804 ADD 812 805 STO 813 806 END 810 28 811 41 812 0 813 0 Trace table: Accumulator Memory address 810 811 812 813 28 41 0 0 [6]

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16 9608/12/O/N/15 © UCLES 2015 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. BLANK PAGE

© Cambridge International Examinations 2015 CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME for the October/November 2015 series 9608 COMPUTER SCIENCE 9608/12 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 12 © Cambridge International Examinations 2015 1 (a) Hard disk – magnetic (storage media) DVD-RW – optical (storage media) Flash memory – solid state (memory device) [3] (b) DVD-RW – uses a single spiral track – only allows write OR read operation to occur as separate operations – requires special packet reading/writing software – in order to write new data to the disc the existing data must be completely erased – performance degrades/becomes unreliable after 1000 record/erase cycles – single sided, 4.7 Gb capacity – disc rotates at different speeds/constant linear velocity DVD-RAM – uses several concentric tracks – allows simultaneous read/write operations – requires no special read/write software – makes use of sectors to store data – repeatedly read, write and erase/100 000 record/erase cycles possible – single or double sided, 4.7 Gb capacity per side – disc rotates at a constant speed/constant angular velocity [4] 2 (a) – laser/light shines onto a surface – through a (polished) ring at the base – the light is reflected from the surface through the ring – sensor detects reflected light – capturing details/photograph of surface (under the ring) – at about 1500 times per second – as the mouse moves the sensor detects changes in the surface detail/photograph – which are translated into movement (change of x and y co-ordinates) – the computer/software updates the position of the cursor on the screen [3]

Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9608 12 © Cambridge International Examinations 2015 (b) Statement Sequence number Paper feed stepper motor activated; sheet of paper fed from paper tray 3 Printer driver translates data into a suitable format for the printer 1 The print head moves across page; ink is sprayed each time the print head pauses for a fraction of a second 4 Paper feed stepper motor advances paper a fraction of a cm after each complete head pass 5 Printer receives data from the computer and stores the data in the printer's buffer 2 [5] 3 (a) (i) 4 6 C [1] (ii) 1 0 1 0 0 0 [1] (b) (i) 1 bit [1] (ii) – 8 bits are needed – Each colour is represented by one of 256 values – values 0 to 255/0000 0000 to 1111 1111 – 256 = 28 [2]

Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9608 12 © Cambridge International Examinations 2015 4 (a) Sampling resolution (two marks) – representation used to write samples in digital sound recording – resolution is the number of distinct values available to encode/represent each sample – specified by the number of bits used to store/record each sample – sometimes referred to as bit depth – the higher the sampling resolution the smaller the quantization error – a higher sampling resolution results in less distortion of the sound – usually 8 bit, 16 bit, 24 bit or 32 bit Sampling rate (two marks) – number of times that the amplitude of (analogue) sound wave is taken/measured – per unit time/per second – higher sampling rate results in more accurate digital representation [4] (b) (i) one mark for correct calculation, one mark for the answer 8 2 16 44100 × × (1 mark) 176 400 bytes (1 mark) [2] (ii) Allow follow through from part (i) on 176 400 1024 1024 176400 60 4 × × × one mark for numerator [2] one mark for denominator (c) any three from: – mp3 is a lossy compressed format – uses psycho-acoustic modelling – and perceptual music/noise shaping – certain parts of the music can be eliminated without significantly degrading the listener’s experience – removes sound that the human ear can’t hear – only keeps sounds human ear can hear better than others – discards softer sound if two sounds played together [3]

Page 5 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9608 12 © Cambridge International Examinations 2015 5 One mark for each correctly placed tick. Activity Ethical Unethical Gives away passwords used in the intruder detection software
Uses source code developed at the software house for the software he develops for his own company
Insists that staff work to deadlines
Turns down training opportunities offered by his employer
Writes and sells software that reads confidential data from client computers
Fakes test results of safety-critical software
Has the software applications developed overseas for sale in his own country
[7]

Page 6 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9608 12 © Cambridge International Examinations 2015 6 (a) Any three from: – program must be resident in (main) memory to be executed – program consists of a sequence of instructions – which occupy a (contiguous) block of main memory – instructions and data are indistinguishable – each instruction is fetched, (decoded) and then executed – instruction fetch and data operation cannot occur at the same time [3] (b) (i) one mark each: – control bus – data bus – address bus [3] (ii) generates the timing signals/generates the signals to synchronise events in the processor / fetch–(decode)–execute cycle [1] 7 (a) lines 8–15 [1] (b) (i) one mark each: – groupSize – groupPrice [2] (ii) lines 10–13 [1] (c) (i) – outputs a prompt for user input/prompts the user for input – returns an input value [2] (ii) – declares – a (local) variable [2]

Page 7 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9608 12 © Cambridge International Examinations 2015 8 Verification (one mark for description, one mark for explanation of need) – needed to ensure that the data entered exactly matches the original source/data is consistent – comparison of two versions of the data – examples include double entry, visual checking, proof reading etc... – does not check data is sensible/acceptable Validation (one mark for description, one mark for explanation of need) – needed to check that the data entered is sensible/reasonable/acceptable/matches required criteria – automatic check by computer – examples include range, type, length, etc. – does not check data is correct [4] 9 (a) (i) 0B . 4 0 . F F . 5 A 1 mark per byte, deduct one mark if no dots or if alternative separator used [4] (ii) Any two from: – composed of four (denary or Hexadecimal) integers – each in the range 0–255/00–FF – each stored in 1 byte/8 bits/stored in 32 bits – (in IPv4) separated into network ID and host ID [2] (b) Maximum 3 marks for URL and maximum 3 marks for DNS – URL = uniform resource locator – reference address to a resource/website on the Internet – includes protocol used /includes domain name – browser software sends URL to DNS – DNS = Domain name system // Domain name service // Domain name server – the true domain name (e.g. cie_exams.co.uk) is resolved/turned into an IP address by DNS – DNS server stores a database/list of URLs with matching IP address – a DNS server may need to pass a request onto another DNS server, (if URL not in its database) – DNS server adds returned IP address and URL to its cache/database – DNS server may return an error message if requested domain name is invalid or does not exist – the DNS service has a hierarchy/or by example – DNS server returns IP address to browser [4]

Page 8 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9608 12 © Cambridge International Examinations 2015 10 (a) Any two from: – To configure the disc for use / initialise tracks and sectors – To initialise a file system (e.g. FAT, NTFS) / create a file directory – To install a boot sector (if creating a bootable disk) – To check all sectors and mark bad sectors [2] (b) One mark each named program + one mark for need Defragmenter – To rearrange blocks that are used for each file to make blocks contiguous (so that file reading is faster) – To reduce head movements (Disk) contents analysis/(disk) repair software/Disc checker – To identify bad sectors so that they can be marked as unusable – Verifies file system integrity and fixes logical file system errors (Disc) compression/file compression – To compress/decompress the contents of the disc, thus increasing capacity Backup software – To store disk contents (somewhere else) in case of disk failure Anti-malware program – To scan for/remove/quarantine viruses and/or other malware (Disc) cleaner – Finds redundant/unnecessary files, gives the user the option of deleting them if disc getting full Disc space analysis – Visually demonstrates the disc usage by showing sizes of files/folders [6]