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CAMBRIDGE INTERNATIONAL EXAMINATIONS

GCE Advanced Subsidiary Level and GCE Advanced Level

MARK SCHEME for the October/November 2013 series

9691 COMPUTING

9691/11 (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 2013 series for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level components and some Ordinary Level components.

Mark Scheme Syllabus Paper

GCE AS/A LEVEL – October/November 2013 9691 11

© Cambridge International Examinations 2013

1 1 mark for method + 1 mark for description Method must match description observation

– watch system in operation first hand – find out first hand where there are bottlenecks/problems with existing system

interviewing – interview passengers and staff face to face – alter questions according to responses given questionnaires

– hand out written questionnaires with pre–tested questions – avoids need for analyst to be present whilst gathering information

look at documentation/data flows

– if any documentation exists, then look through it to see what data needs to be handled by new system

– observe the data flow through the system to find out volumes of data, how data is collected, how data is processed and so on [4]

2 (a) Any five from:

– graphics showing the process – graphics mimic the process accurately/show how process links up – use colours e.g. green = ON and red = OFF – use flashing colours/sounds to show faults – ability to click on graphics to show history/status – easy to understand/use interface – ability to easily move between process screens allowing monitoring of all stages in

process – use of sound to warn of problems or to indicate that monitoring is functioning correctly – use of input devices such as touch screens and trackerballs – use of output devices such as loud speakers/beepers and printers [5]




(b) 1 mark for each device and 1 marks for each reason touch screen

– to select (graphics to view status or start/stop parts of process) – to be able to easily navigate to other screens in the process

trackerball

– to select (an item on the screen to change its status)

– to be able to easily navigate to other screens in the process keyboard

– to input values or type in queries/enter commands [4] 3 (a) One point from each: verification

– this is a way of preventing errors when data are copied from one medium to another

– e.g. double entry or visual checks on data

– verification does not check to see if data makes sense or are within acceptable

boundaries;

– it only checks to see if original and copied data match exactly validation

– this is a computer check on input data

– see if data matches certain criteria and are reasonable

– example e.g. range check [2] (b) (i) length check [1] (ii) range check [1]




(c) (i) 5 4 3 2 1 3 0 4 5 ? sum = (5x3) + (4x0) + (3x4) + (2x5) = 15 + 0 + 12 + 10 = 37 divide 37 by 11 and get 3 remainder 4 check digit is 4 (1 mark for a reasonable calculation + 1 mark for correct check digit allow follow through)

[2] (ii) Any two points from:

– check digit for 34921 re–calculated

– check digit value should be 7 (using modulo 11)

– error will be flagged check digit is shown as 1 in transmitted number [2] 4 (a) 1 mark for each correct logic gate

[4]




(b)

A B C 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] 5 (a) interrupt

signal sent to the processor (which causes a break in the execution of the current routine) [1]

(b) Any three from:

– data sent to printer buffer from memory

– buffer is then emptied to printer allowing user to get on editing document

– when buffer empty an interrupt is sent to processor from printer requesting more data

– current job suspended while buffer refills

– use continues editing document whilst buffer emptied contents to printer

– idea of interrupt priorities [4]

} } } }

1 mark

1 mark

1 mark

1 mark




(c) – response depends on the software package – produces a dialogue box alerting user that virus has been found inviting user to “clean

up” the infected file

– some systems remove viruses automatically and don’t request user “permission”

– quarantine the infected file/virus [2] (d) Any two points from:

– OS will allow one user at a time to use the computer

– each approved user is identified by a user id/password

– allows multi-tasking

– provides security for user files/profiles [2] 6 (a) RAM

– contents can be altered/written to

– holds program/data currently in use

– volatile/temporary memory/contents lost on switching off

– usually has greater memory capacity than ROM ROM

– contents can be read only/can’t be altered

– holds bootstrap/BIOS/system data

– non–volatile/permanent memory/retains contents on switching off

– MAX 2 points from ROM and MAX 2 points from RAM [3] (b) RAM

– holds the data gathered from the sensors during monitoring

– holds user information entered into system

– holds part of OS/program, in current use ROM

– holds program that is used to control the data logger

– holds the start-up routines when data logger set up for monitoring [2]




(c) 1 mark for device + 1 mark for application

Device application

– barcode/QR reader automatic stock control

library systems

– rfid tracking live stock

timing athletes automatically in races

– biometrics security systems

passports

– magnetic stripes credit/debit cards

hotel key cards

– OCR checking signatures on documents

– voice recognition helping blind people interface with a computer

system

– smart (card) system loyalty cards

passports

– OMR automatically marking exam papers

– MICR banking/cheques [2]

(b) Any four from:

– pH and oxygen sensors send data/signals to the data logger

– ADC

– data is stored in data logger’s memory

– data is sampled at a set time interval (depending on memory size)

– data logger taken back to laboratory after monitoring period

– data is downloaded to a computer

– data logging software interprets information…

– …and shows graphs of how oxygen and acidity levels changed over the monitoring

period

– built in routines warn if levels dangerously high [4]




7 (a) 1 mark for each benefit and 1 mark for each drawback benefit drawback bus – requires less cabling than the – if there is a fault in the central – other topologies cable, whole system affected – cheapest system to set up – doesn’t work well under heavy loading – less secure star – failure in any connection and – if central hub fails, whole network fails network still functions – easier to identify faults – more expensive to set up – easier to expand network – each node can have different kind of cable – a more secure network ring – works well under heavy loading – faulty connection can cause whole network to fail – possible to form very large – difficult to expand this type of networks network – less secure [6] (b) 1 mark per point LAN – hub – (cat 5) network cabling – network interface card (NIC) – gateway – server – bridge – switch WAN all the above plus: – broadband modem – telephone cabling/radio links/satellite links – router [3]




8 (a) Any three from:

– use of formulas

– inbuilt functions

– automatic graphs produced

– automatic re-calculation of cells

– “what if” scenarios/predictions

– possible to install macros [3] (b) 1 mark for each advantage and 1 mark for each disadvantage advantages

– often get better customer support since in direct contact with software designers/writers

– designed and written to meet unique user’s specific requirements

– writers of software can develop it so it will not interfere with other software used in the

company

– users get exactly what they want – therefore usually more user-friendly

– any modifications needed later on can be done more easily and quickly

– other companies cannot use the software (for the company alone) disadvantages

– much greater dependence on software company (could go out of business)

– unlikely to be as well developed as off-the-shelf products

– usually much more expensive since all development costs have to be met by the

customer

– development time may be very lengthy

– can be a gamble since final package may not exactly meet user requirements in a

reasonable time scale

– no user groups or eq. [4] (c) Any two from:

– specialist control applications (e.g. nuclear plants)

– specialist monitoring applications (e.g. chemical process)

– modelling tasks

– virtual reality applications

– hospital/medical monitoring

– air traffic control [2]




9 (a) – mimics knowledge and experience of human experts – uses knowledge base and inference engine to solve problems in a “human like” manner [1] (b) 1 mark per point: Cannot get max unless use all three parts inputs

– engineer inputs the fault(s)

– answers on screen questions that are based on previous responses

– uses an interactive interface processes

– expert system analyses data

– inference engine compares data/makes reasoned conclusions…

– …with that held in/based on data in knowledge base

– …uses the rule(s) base/set of inference rules

– until matches are found outputs

– percent probability of fault

– how to fix the problem

– outputs reasons it produces a particular answer [7]




9691 COMPUTING

9691/12 Paper 1 (Written Paper), maximum raw mark 75






1 (a) Any five from: – answers are represented by marks on paper in particular positions – the answer sheet is input into OMR reader/answers are scanned – reflection of light from the marks is different to that reflected off the background paper – the information read is converted into digital values – (the reader takes note of the position of the marks) and reports the coordinates of the

marks – position determined by timing bars at the side (of the survey form) – only the position of the marks is recognised, not the marks themselves – the positions are compared with a template of correct positions stored in the computer – the number of matches between the template and the person’s attempt provides the final

indication of how many answers were correct – mention what happens if the person doing the test fills in too many lozenges/corrects an

answer – mention what happens if person filling in form used non-reflective ink/use of special

ink/use of special ink prevents OMR reading text. [5] (b) (i) Any two from: – software that can reduce the size of files/to save memory – without losing any of the information contained in the file – example of how this works – for faster file transmission – if attachment sizes are limited [2] (ii) Any two from: – text file/pdf – photographic files (JPEG)/image – sound files (MP3/4)/video files – ZIP/TAR/GZIP (accept description rather than name the file type) [2]




2 If there are 11 or more lines – 1 for each additional line

[10]

Note: ALU maps to items: 2, 5 and 7 Control Unit maps to items: 1, 3 and 8 RAM maps to items: 4, 9 and 10 ROM maps to items: 6

Manages execution of instructions

Carries out arithmetic operations such as addition and multiplication

Fetches each instructionin turn

Stores program in current use

Carries out bit shifting operations

Stores boot-strap loader

Carries out operations such as AND, OR, NOT

Issues timing signals

Stores part of operatingsystem in current use

Stores data in current use

ALU

ControlUnit

RAM

ROM




3 (a) Any two from: – transmission can be in both directions at the same time – along several data wires/lines/one data line per bit/1 byte at a time [2] (b) Any two from: – to establish a set of rules before data transmission… – rate of transmission (baud or bps) – whether transmission is to be synchronous or asynchronous – whether serial or parallel transmission – whether data is transmitted in half duplex or full duplex mode – both ends use same parity – data transmitted in both directions at same time so protocols needed to control direction

of data travel [2]




4 (a) 1 mark for name + 2 marks for features – CAD features: can be given if wrongly named – 3D (modelling) is possible – can calculate the cost of building each “ride” – has features such as rotate, zoom, vector diagrams … – can carry out simulations on each “ride” – create engineering drawings/blue print – library of parts (using other “rides” as a template) – links into CAM – prototype [3] (b) Any four points from: – if monitoring safety aspects, e.g. corrosion, temperature, pressure… – sensors on the “rides” will constantly send data back to computer/sends continuous

signals to the computer – the data will be converted into digital format – sensor data will be compared to engineering data stored in computerif any values are out of specific – computer shows a flashing red graphic on screen … – … or computer triggers an audible warning – camera data sent to computer – compares image against already stored images – sends warning to control room if significant differences detected – if monitoring “rides”, images are compared frame by frame for safety [4] (c) Any four points from: – graphics are animated to show movement of “rides” – use of graphics to represent the “rides” – consistent layout on all 3 screens – reasons why you need three screens (grouping ride types etc.) – sensor data and “rides” graphics show GREEN if OK/RED if NOT OK (red for danger) – use of flashing colours to warn of problems – interface should be easy to use/understand/interpret – ability to navigate easily from screen to screen/”ride” to “ride” – by clicking/selecting a graphic, status + history can be shown on screen – use of touch screens and trackerball to select and navigate [4]




5 (a) – items held in logical/numerical order – using barcode/ID (to determine the order) [1] (b) example diagram:

0 000 000 000 data 000 000 001 data

1 099 999 999 data 100 000 000 data 100 000 001 data 2 199 999 999 data 3 200 000 000 data 210 333 222 data 9

marking points (either refer to diagram or a description of diagram): – digits 0 to 9 used (as in diagram) – as index – each leading to sequence of barcodes – each barcode/product ID points to data – item with barcode/product ID 210 333 222 found and data (e.g. price) retrieved [3]




6 (a)

counter values coloured lights (output)

A

B

C

R

G

Y

0

0

0 1

0

0

0

0

1 1

0

0

0

1

0 1

0

0

0

1

1 1

1

0

1

0

0 0

0

1

1

0

1 0

0

1

1

1

0 0

0

1

1

1

1 0

1

0

(1 mark per 2 ROWS as shown in diagram) [4]

}

}

}

}




(b) There are three possible solutions here. But in ALL three cases:

• The logic circuit for R is worth 1 mark • The logic circuit for G is worth 1 mark • The logic circuit for Y is worth 3 marks

Option 1 Marking points: – for circuit “R” 1 mark for correct NOT gate (showing correct input and output) – for circuit “G” 1 mark for correct AND gate (showing correct input and output) – for circuit “Y”: – 2 marks for the NAND gate (MUST have both inputs correct to get the marks) – 1 mark for the AND gate (MUST have correct inputs and output to gain the mark) [5]




Option 2 Marking points: – for circuit “R” 1 mark for correct NOT gate (showing correct input and output) – for circuit “G” 1 mark for correct AND gate (showing correct input and output) – for circuit “Y”: – 1 mark for the first AND gate (MUST have both inputs correct to get the marks) – 1 mark for the NOT gate following straight after the AND gate – 1 mark for the second AND gate (MUST have correct inputs and output to gain the

mark) [5]




Option 3 Marking points: – for circuit “R” 1 mark for correct NOT gate (showing correct input and output) – for circuit “G” 1 mark for correct AND gate (showing correct input and output) – for circuit “Y”: – 1 additional mark for the first AND gate – 1 mark for the NOT gate following straight after the AND gate – 1 mark for the second AND gate (MUST have correct inputs and output to gain the

mark) [5]




7 (a) NOTE: need different validation check for each of the three fields: If a name and description are both given they MUST match for a mark. (i) present salary – range check; for example, $1000 to $5000 per week – type/character check – salary must be digits only – presence check (ii) staff name – type/character check – name must be non-numerical characters only – string – presence check (iii) staff id – format check (i.e. format nn/xxxxxxx) – presence check [3] (b) (i) title and sex – consistency check – if someone selects Mr then they can’t choose female in the sex field (ii) date of birth and date joined company – check that second date is later than date of birth field [2] (c) 1 mark for choice of method + 2 marks for correct description Description marks MUST match stated method parity check – number of one in the byte should be even or odd (i.e. even parity or odd parity) – both sender and receiver use the same parity – if byte arrives at destination with wrong parity, error has occurred – use of horizontal and vertical parity checking to identify incorrect bit – parity bit is sent with the byte/data check sum – bytes added together at sending stage – value from addition/checksum sent with transmitted bytes – received bytes go through same addition process – the two sums are compared; if different a transmission error has occurred [3]




8 (a) 1 mark for method + 1 mark for benefit (If benefit described as part of description, allow carry over and award marks) observation – systems analyst can see what is happening first hand – systems analyst doesn’t have to rely on biased opinions – does not take up client time (written) questionnaires – questions are pre-determined/fully tested questions – people can take the questionnaires away so systems analyst doesn’t need to be present – useful where there are a large number of users interviewing – systems analyst can vary/extend the questions according to answers given or depending

on who is being interviewed – answers tend to be more honest and embellished when compared to method of

questionnaires (examine) documentation/data flows – systems analyst can use this method to describe what hardware and software may be

required – this method can be used to determine file structures, etc. – to determine input and output requirements – to determine data volumes/size [6] (b) (i) Any one from: – for analyst/programmers – in case of further development/upgrades – maintenance – in case there are errors in the system and need to be corrected [1] (ii) Any three from: – systems flow diagrams/DFDs/JSD – variables used/data structures/data dictionary – hardware/software requirements – purpose of the system/log of any revisions – algorithms/program flowcharts/JSP – annotated listing/programming code – testing procedures/test plan – test data and results – validation routines – meaning of error messages from the system [3]




9 (a) – (expert system) shell [1] (b) 1 mark for each part user interface – allows system to ask questions and user to answer them – very often simple Yes/No answer dialogue – allows communication between a user and the expert system explanation system – tells user how system made its decision(s)… – …usually in response to user asking WHY inference engine – applies rules in the rule base to the knowledge base – makes reasoned conclusions using information from facts/knowledge base – acts as a reasoning engine (knowledge base) editor – allows creation of hierarchical knowledge base – allows user to create rules for rules base – setting knowledge base properties – allows creation/changing/updating (of knowledge base) rule(s) base – made up of a series of inference rules – allows inference engine (to draw conclusions) – allows a set of rules to draw up a conclusion knowledge base – a type of database… – …which allows complex data storage and retrieval – contains date gathered from the experts [6] (c) Any three from: – lack common sense – errors in knowledge base can cause problems and lead to incorrect conclusions – cannot adapt to changing environment unless the knowledge base is updated on a

regular basis/out dated – expensive system to set up – users need extensive training which is expensive and time consuming – limited to what is stored in the expert system/cannot respond to usual circumstances [3]




9691 COMPUTING

9691/13 (Written Paper), maximum raw mark 75






1 (a) hardware

- physical/electronic parts of the computer

software

- instructions/programs [2] (b) 1 mark for each device + 1 mark for corresponding reason input

touch screen - to choose where to sit in cinema - select payment options - select number of seats

keypad

- to input PIN - to input number of seats

magnetic stripe reader/card reader - to read data from credit card/debit card when making payment

sensors - to count/recognise money if paying by cash for tickets

output printer - to print the tickets/receipt

screen - instructions to the customer - show prices of tickets - show available seats on seating plan - show which films are showing that week

speakers - to indicate an error or that purchase procedure is OK [8]




2 (a) (i) 173 [1] (ii) (0) 1 0 0 1 0 0 1 [1] (b) - symbols recognised/used by a computer - often equates to symbols on a keyboard [2] (c) - represented by a set of bits - each set of bits is unique for each character - ASCII/UNICODE is a common set used - example of set of bits [2] 3 (a) 1 mark for name of software + 2 marks for reasons

- CAD reasons

- 3D (modelling) is possible - possible to calculate cost of the final bathroom - has features such as rotate, zoom, vector diagram, etc. - possible to create drawings/blue prints - library of parts (available bathroom items, for example) - wire frames (for bespoke designs) - links with CAM (for specialist items) [3]




(b) (i) Max of three points from:

- temperature sensor used here (NOT heat sensor) - the sensor sends data continuously to microprocessor - the data is first converted to digital (**) - microprocessor compares sensor reading with temperature selected by user - if temperature is higher, then microprocessor will send a signal… - …to actuators to open cold water valve more … - …and to reduce hot water flow by closing hot water valve - if temperature is lower, then microprocessor will send a signal… - …to actuators to open hot water valve more … - …and to reduce cold water flow by closing cold water valve - if temperature is within acceptable range, no action taken - if cold water supply fails, system shuts down - if temperature > = 35C and sensor detects human hand (for example), the system

stops the water flow (ii) Max of three points from:

- if hand detected, “movement” sensor send signal to microprocessor - signal is first converted to digital (**) - microprocessor sends signal to actuator…(**) - … to open both valves - when hand removed, “movement” sensor sends signal to microprocessor - signal is first converted to digital (**) - microprocessor sends signal to actuator…(**) - … to close both valves - microprocessor constantly monitors for signals from the sensors [6]

4 (a) 1 mark for media type + 2 marks for examples

optical

- DVD-RAM (playback/record at same time) - CD-R/CD-RW (recording music or files) - blu-ray/DVD (recording films)

solid state

- memory sticks (portable devices allowing easy transfer of files between computers) - memory cards in cameras/mobile phones (to store photos) - memory in MP3 players (to store music files) [6]




(b) Any four points from:

- buffer is a temporary storage device - data transferred from primary memory to buffer - when buffer full, processor can do other tasks - buffer emptied to memory device - when buffer empty, sends interrupt… - …to processor - …requesting more data to be sent to buffer - according to priorities [4]

5 (a) Any four points from:

- purpose of the system - how to log on/log off the system - installation procedure/load/run software - file utilities (save, sort, search, amending records etc.) - screen layouts (input formats) - print layouts (output formats) - hardware and software requirements) - sample runs (with test data and results) - error handling/meaning of errors - troubleshooting guide/FAQs [4]

(b) Any four points from:

- combinations of colours to allow contrasts/highlight key points - colours should be consistent (e.g. everything to do with purchasing of electronic toys will

be shown in blue) - avoid red/green colour combinations because customer may be colour blind/avoid

flashing colours in case they cause epileptic fits) - screen layout should follow natural reading pattern (i.e. left to right, top to bottom) - large buttons to allow easy choice/screen navigation - stages in ordering process should be simple to follow/not use complex or ambiguous

language) [4]




6 (a) [7]

(b) Any four from:

- messages assembled into one or more packets - includes address and control codes - these packets can be sent independently through the network. - …collected together and re-assembled into original information at the destination - individual packets do not have to travel by the same route - unlike conventional switching where a channel is established and left open for duration

of entire transmission [4]

If the central hub fails, the whole network fails

Works well under load

Poor performance under heavy loading

If one connection fails, the other terminals are not

Less cabling required

Different communication media can be used for different nodes

Can be used for wide area networks

Bus

Star

Ring




7 (a) Any four points from:

- training will be necessary (this can be expensive for the company and it also takes the workers away from their job while undergoing training)

- possibility of redundancies (for reasons above) but also because the new computer systems may require fewer staff to do the work

- greater productivity – production of work will take less time (e.g. CAD software allows modifications to drawings to be made in a fraction of the time manually)

- possibility of working from home (can email work, use VoIP etc.) - better working environment for staff (less noisy) - creation of new jobs….all computer related (e.g. computer maintenance) [4]

(b) 1 mark for each benefit and 1 mark for each drawback off-the-shelf benefits

- usually less expensive since the development costs can be spread over many purchasers of the software

- they are frequently more sophisticated since the money generated from large sales (often global) allows more development work to be done

- there will usually be user groups who can give help and support - the ability to export/import files into/from other packages is often easier since they are

more likely to be compatible - the software is available immediately – there is no need to wait while it is being written

and developed - the software is usually relatively “bug free” since it has been highly developed using

feedback and targeted user groups. drawbacks

- the software tends to be over-complex since it tries to cover as many aspects as possible; the average user will probably only use a small fraction of the features available

- because of the unwanted features, the software tends to be over-complex in use - the software may not exactly fit the requirements of the user and may be a compromise - any major problems for a user (requiring a re-write) will not be resolved quickly – a

software re-write may cause problems for other users and may even cause software instability




custom-written benefits

- these are designed and written to meet the user’s specific requirements; consequently, they will be more efficient and won’t contain unwanted features

- the writers of the software can develop it so that it will not interfere with other software being used by the company; this will avoid any software clashes

- it is frequently easier to use since the software can be written in conjunction with the end users in mind (the users get exactly what they need)

- any modifications needed (e.g. due to changes in the business requirements) can be done more easily and more quickly since the changes are probably specific to the company

- usually better customer support since the users can be in direct contact with the software designers/writers

drawbacks

- there is much greater dependence on the software company; e.g. if they go out of

business then future support may be non-existent - it is unlikely to be as well developed as “off the shelf” software - it is usually far more expensive since the development costs have to be met fully by the

user - the development time may be quite lengthy, particularly if the application is unique or

complex - in some ways, the company takes a gamble – the final package may not actually meet

the user requirements especially if the development time is long and the company’s needs have changed in the meantime [4]




(a) [4]

A

B

C

X

0

0

0

0

0

0

1

0

0

1

0

1

0

1

1

0

1

0

0

1

1

0

1

0

1

1

0

1

1

1

1

0

}

}

}

}

1 mark

1 mark

1 mark 1 mark




(b) 1 mark per correct logic gate:

PLEASE NOTE: If a candidate has attempted to simplify the logic circuit to either: X = (A NAND B) OR (B AND C) or: X = (A NAND B) OR C then award 3 marks for the NAND gate and then either 1 mark each for the OR gate and AND gate in the first expression or 2 marks for the OR gate in the second expression. [5]

9 (a) (i) Green [1] (ii) Colour (3) [1] (b) (i) Yellow [1] (ii) Colour (5) [1]

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