Principle Operation of Devices Revision - · PDF filePrinciple Operation of Devices Revision...

Principle Operation of Devices Revision

AQA Computing AS-Level COMP2

2014

53 minutes

53 marks

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Q1. A Radio Frequency Identification (RFID) system is made up of a transponder built into an RFID tag and an interrogator or reader. One example of use is to detect unauthorised removal of library books from a library.

Explain the principles of operation of this RFID system.

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Q2. There are various formats of optical storage media currently available.

(a) Choose the most appropriate medium from the list below that would be best suited to the purpose given. Write your answer in the Medium column in the table below. You must not use the same medium more than once.

CD-ROM, CD-R, CD-RW, DVD-R, DVD-RW, Blu-Ray

(4)

Purpose Medium

To distribute 300MB of commercial software

To store a 20GB high definition movie file

To use for a 3GB archive of the data on a school server

To create a copy of a 60 minute audio music album

(b) Describe how data is written to and read from a CD-R disk.

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(c) A series of word-processed documents have been archived onto CD-R.

State two reasons why in 20 years’ time it might be impossible to open up these documents.

Reason 1: ......................................................................................................

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Reason 2: ......................................................................................................

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(Total 9 marks)

Q3. In 1995, a high capacity hard disk drive had a storage capacity of 512 megabytes. In 2012, a typical hard disk drive of the same physical size had a capacity of 1 terabyte.

(a) Describe the principles of operation of a hard disk drive.

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(b) How many times greater is the storage capacity of a 1 terabyte hard disk drive than that of a 512 megabyte hard disk drive?

Show each stage of your working.

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Final answer .................................................................................................. (1)

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(c) Give one development in the design of hard disk drives that has enabled this increase in storage capacity.

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(d) If you are considering purchasing a high-end desktop or laptop you might be offered the option of a solid-state drive (SSD) rather than a traditional hard disk drive.

A solid-state drive is a data storage device that uses solid-state memory, similar to that in USB flash drives (memory sticks), to store data that is accessed in a similar way to a traditional hard disk drive.

Ignoring any differences in price and assuming that both drives have the same capacity, state two reasons why you might choose the solid-state drive.

Reason 1 .......................................................................................................

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Reason 2 .......................................................................................................

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(Total 9 marks)

Q4. (a) Here is a list of input devices:

smart card reader, Radio Frequency Identification (RFID) reader, flatbed scanner, touch-sensitive screen.

For each of the situations below, state the name of the most appropriate input device from the list above. You should not use the same device more than once.

(i) Information kiosk at a railway station

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(ii) Payment for food at a school canteen

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(iii) To identify a book being removed from a library without authorisation

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(b) Describe the principles of operation of a flatbed scanner.

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(Total 7 marks)

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Q5. Compare the principles of operation of a laser printer and an inkjet printer when printing. Do not include information about how the data is transferred from the computer to the printer.

In your answer you will be assessed on your ability to use good English, and to organise your answer clearly in complete sentences using specialist vocabulary where appropriate.

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Q6. (a) Give two differences between primary and secondary storage.

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(b) Explain the principles of operation of a hard disk drive.

Your answer to this question will also be assessed on your ability to organise your answer clearly and coherently in complete sentences, using specialist vocabulary where appropriate.

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(Total 8 marks)

Q7. Some European governments are introducing electronic passports for their citizens. An electronic passport stores data about the passport holder using a Radio Frequency Identification (RFID) tag.

(a) An electronic passport stores data about some biometric properties of the passport holder.

(i) What is meant by the term biometric property?

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(ii) Give an example of a specific biometric property that could be stored on a passport to identify the holder.

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(b) Explain how the RFID tag could be read at passport control in an airport.

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(Total 4 marks)

Q8. A supermarket uses a computerised stock control system. Each product is identified by a unique product code which is printed on the product as a bar code. The bar codes are input into the stock control system at the till using a bar code reader. One of the digits in the bar code is a check digit.

(a) Describe the principles of operation of a bar code reader, excluding the use of the check digit.

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(b) Explain the purpose of the check digit.

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(c) Some unpackaged items such as loose fruit and vegetables do not have a product code printed on them.

Name an input device that the till operator could use to enter details of these items.

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(Total 6 marks)

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M1. 1. reader sends radio frequency energy / wave; 2. to the antenna of the RFID tag in the book; 3. The RFID tag is energised by the reader / this energy; 4. the transponder (in the tag) sends the data signal; 5. the reader near the exit receives the data signal;

Max 2 [2]

M2. (a)

Note: Mark first occurrence of each medium 4

Purpose

To distribute commercial software

To store a 20GB high definition movie file

To use for a 3GB archive of a school server

To create a copy of a music album

(b) Write: To write data a high powered / high frequency laser makes sections less reflective / burns a pit; R laser writes grooves/tracks;

Read: A low powered laser is used to read data back from the disk; Mechanism: The difference between reflective and non-reflective parts / pits and lands indicates the 1s and 0s; The data is stored as a continuous spiral track;

One mark each for write, read and mechanism. Note: a laser is used to read and write data (1 mark only)

Max 3

(c) No hardware exists to read CD-R disks; The CD-R medium has become corrupted // CD-R is scratched / damaged / degraded; Support for file format no longer available // no software capable of reading format data stored in CD-R;

Max 2 [9]

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M3. (a) Magnetic (medium);

Binary digits / bits / 0s and 1s / data represented by magnetising spots on disk // changing magnetic properties of disk; Disk made up of platter(s); Disk divided into tracks and sectors; A either tracks or sectors alone Tracks are concentric circles // organised into cylinders Drive head can move in / out // moves to track / cylinder // moves radially; Disk continuously spinning (while in operation); Disk spins at high speed // feasible example of speed; Data read / written as correct sector passes under read / write head; A drive head Data transferred in sectors / blocks; Medium and drive / device in sealed enclosure; Hard disk drive is a random access device; A Head parked / not over disk when not in use // head must not touch surface when in use; A Use of cache / buffer to speed up data transfer;

Max 3 if candidate talks about lasers / making holes / pins / engraving Max 4

(b) 512 MB x 2 = 1024 MB = 1GB 1GB x 1024 = 1 TB

2 x 1024 = 2048

Award mark for a clear movement between MB – GB - TB making use of 1024 ;

Final answer: 2048;

Acceptable alternative (as many hard drive manufacturers do not use the 1024 principle) :

1 TB = 1000 GB = 1000000 MB;

1000 000 / 512 = 1953.125; (mark to be awarded for understanding the calculation needed)

Final answer : 1953.125;

A Accept a final answer that has involved some approximation as a no calculator paper.(2000;)

Alternative

240 / 229 ; = 211;

Max 2

(c) More platters (which are packed closer); Greater density of data on each platter; More tracks on a platter // more cylinders; Change to perpendicular magnetic domains; Ability to write smaller magnetic domains/parts // smaller read / write heads; Use of different alloy materials for the platters;

Max 1

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(d) Faster access speed // faster booting of operating system // faster data transfer / read / write speeds; Silent operation; Are lighter; Less heat generated; Less power required // longer battery life; Less susceptible to damage from physical shocks // more robust (due to no moving parts); A quicker as no need to wait for read / write head to move // sector to be underneath read / write head; NE quicker (without explanation) NE better performance (without explanation)

Max 2 [9]

M4. (a) (i) Touch (–sensitive) screen;

1

(ii) Smartcard reader // RFID reader // Radio Frequency Identification reader; Touch (sensitive) screen; (if not awarded for part i)

Max 1

(iii) RFID reader // Radio Frequency Identification reader; (if not awarded for part ii) 1

(b) Document placed onto glass (pane) // scanner has a glass pane; Under which is a bright light / rows of red, green & blue LEDS; and array of optical sensors / CCD array; covered to exclude ambient light; sensor array / light moved steadily (under glass) to scan whole document; the reflected light is converted into an equivalent electrical signal; more light reflected from bright regions than dark regions; Link between reflected light and colour explained;

Max 4 [7]

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M5. Laser Page printer; Print drum coated in (negative static) charge; Printer generates bit map of page; Laser beams shone / directed at / “draws” on print drum; Via rotating (octagonal) mirror; Laser is modulated (turned on & off); Laser removes / neutralises / reverses electric charge on drum; where image should be dark / black; Toner is given (negative) charge; Charged drum picks up toner; Toner transferred from drum to paper; (“from drum” may be implicit in order of answer) Toner is fused / bonded / melted / stuck to paper by (heated rollers / pressure); (must be clear that toner is already on paper when it is fused, not still on drum) I incorrect charges e.g. positive when should be negative Ink Jet Heater behind ink reservoir is warmed; Vaporises droplet of ink. Expands and forces small ink blob out onto paper; Electricity applied to piezoelectric crystal; Deforms crystal shape; Fires/squirts / shoots spots of ink; NE places Some colours produced from mix of ink spots fired together; Heater turns off – ink cools sucks remainder of droplet back in. Repeated for all colours and each nozzle; Electric current switched off piezoelectric crystal returns to original shape; Print head moves across each line of paper / repeated for each part of each character // Prints line by line; Ink dries before paper emerges from printer; A laser / ink jet printer uses (black), cyan, magenta, yellow (Note – only accept this point once)

8

To achieve a mark in this band, candidates must meet the subject criterion (SUB) and 4 of the 5 quality of language criteria (QLx).

7–8

SUB Candidate has provided a clear explanation of principles of operation,

including at least 7 of the points listed above of which 3 must come from each printer operating explanation.

QL1 Text is legible. QL2 There are few, if any, errors of spelling, punctuation and grammar. Meaning is clear.

QL3 The candidate has selected and used a form and style of writing appropriate to the purpose

and has expressed ideas clearly and fluently. QL4 Sentences and paragraphs follow on from one another clearly and coherently. QL5 Appropriate specialist vocabulary has been used.

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5–6

SUB Candidate has provided a clear explanation of principles of operation,

including at least 5 of the points listed above of which 2 must come from each printer operating explanation.

QL1 Text is legible. QL2 There are few, if any, errors of spelling, punctuation and grammar. Meaning is clear.

QL3 The candidate has selected and used a form and style of writing appropriate to the purpose

and has expressed ideas clearly and fluently. QL4 Sentences and paragraphs follow on from one another clearly and coherently. QL5 Appropriate specialist vocabulary has been used.


3–4

SUB Candidate has provided a limited explanation of principles of operation,

including at least 3 of the points listed above. Candidate does not need to cover both types of printer.

QL1 Text is legible. QL2 There may be occasional errors of spelling, punctuation and grammar. Meaning is clear.

QL3 The candidate has, in the main, used a form and style of writing appropriate to the purpose,

with occasional lapses. The candidate has expressed ideas clearly and reasonably fluently. QL4 The candidate has used well-linked sentences and paragraphs. QL5 Appropriate specialist vocabulary has been used.

To achieve a mark in this band, candidates must meet the subject criterion (SUB). The quality of language should be typified by the QLx statements.

1–2

SUB Candidate has provided a weak explanation which covers at least 1 of the

points listed above for 1 mark or 2 points to get 2 marks. QL1 Most of the text is legible.

QL2 There may be some errors of spelling, punctuation and grammar but it should still be

possible to understand most of the response.

QL3 The candidate has used a form and style of writing which has many deficiencies.

Ideas are not always clearly expressed.

QL4 Sentences and paragraphs may not always be well-connected or bullet points may have

been used. QL5 Specialist vocabulary has been used inappropriately or not at all.

Candidate has not made reference to any of the points listed above. 0

Note: Even if English is perfect, candidates can only get marks for the points made at the top of the mark scheme for this question.

If a candidate meets the subject criterion in a band but does not meet the quality of language criteria then drop mark by one band, providing that at least 3 of the quality of language criteria are met in the lower band. If 3 criteria are not met then drop by two bands.

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M6. (a) Secondary store is non-volatile / stores a permanent copy / keeps contents when

computer turned off whereas primary store is volatile / temporary / loses contents when computer turned off;

Secondary store is not directly accessible to the processor / outside main memory whereas primary store is directly accessible to processor;

Capacity of primary store is limited by width of address bus whereas no limit on capacity of secondary store;

Data in primary store can be accessed more quickly than data in secondary store; A Answers where converse is implied rather than stated. R Secondary store is long-term whereas primary store is short-term. R Secondary store has a higher capacity than primary store.

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(b) Magnetic (medium); Binary digits/bits/0s and 1s/data represented by magnetising spots on disk // changing magnetic properties of disk; Disk divided into tracks and sectors; A either tracks or sectors alone Drive head can move in/out // moves to track // moves radially Disk continually spinning; Disk spins at high speed // feasible example of speed; Data read/written as correct sector passes under read/write head; A drive head Data transferred in sectors/blocks; May be multiple platters; A surfaces One head per platter; Use of cache/buffer to speed up data transfer; Medium and drive/device integrated // medium in sealed enclosure; Head parked / not over disk when not in use; Must use accurate terminology as this is the quality of language question


5–6

SUB Candidate has provided a clear explanation of principles of operation, including at least 5 of the points listed above.

QL1 Text is legible QL2 There are few, if any, errors of spelling, punctuation and grammar. Meaning is clear.

QL3 The candidate has selected and used a form and style of writing appropriate to the

purpose and has expressed ideas clearly and fluently. QL4 Sentences and paragraphs follow on from one another clearly and coherently. QL5 Appropriate specialist vocabulary has been used.

To achieve a mark in this band, candidates must meet the subject criterion (SUB) and 4 of the 5 quality of language criteria (QLx)

3–4

SUB Candidate has provided a limited explanation of principles of operation, including at least 3 of the points listed above.

QL1 Text is legible.

QL2 There may be occasional errors of spelling, punctuation and grammar. Meaning is

clear.

QL3 The candidate has, in the main, used a form and style of writing appropriate to the

purpose, with occasional lapses. The candidate has expressed ideas clearly and reasonably fluently.

QL4 The candidate has used well-linked sentences and paragraphs. QL5 Appropriate specialist vocabulary has been used.

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To achieve a mark in this band, candidates must meet the subject criterion (SUB). The quality of language should be typified by the QLx statements.

1–2

SUB Candidate has provided a weak explanation which covers at least 1 of the points listed above for 1 mark or 2 points to get 2 marks.

QL1 Most of the text is legible.

QL2 There may be some errors of spelling, punctuation and grammar but it should still be

possible to understand most of the response.

QL3 The candidate has used a form and style of writing which has many deficiencies.

Ideas are not always clearly expressed.

QL4 Sentences and paragraphs may not always be well-connected or bullet points may

have been used. QL5 Specialist vocabulary has been used inappropriately or not at all.

Candidate has not made reference to any of the points listed above. 0

Note: Even if English is perfect, candidates can only get marks for the points made at the top of the mark scheme for this question.

If a candidate meets the subject criterion in a band but does not meet the quality of language criteria then drop mark by one band, providing that at least 3 of the quality of language criteria are met in the lower band. If 3 criteria are not met then drop by two bands.

6 [8]

M7. (a) (i) A biological / physical / behavioural (A by example) property of a person that

can be used to identify them / unique; R examples alone

1

(ii) Fingerprint; Retina / Iris pattern / scan; R Eye scan Facial structure / scan; R Photo of face DNA fingerprint / profile; R DNA Voice pattern /print; Ear print;

Max 1

(b) RFID reader/scanner (at passport control) transmits / sends signal; Signal which activates / energises / induces current RFID transponder / tag; RFID transponder / tag transmits / sends data by radio(wave); Electrical / physical contact between tag and reader not required // tag must be near to reader; Passport may need to be unlocked using Machine Readable Zone(MRZ) / key;

Max 2 [4]

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M8. (a) For Photodiode System:

Light / laser / LED / Infra-red light shone at bar code; NE beam (Moving) mirror / prism moves light beam across bar code / / user moves reader across bar code; NE beam Light reflected back; Black/white bands reflect different amounts of light / / black reflects less light / / white reflects more light; Light sensor / photo sensor / photo diode / CCD measures amount of reflected light; Light reflected converted into an electrical signal; A convert reflection to (binary) numbers / characters (Electrical form of) reflection analysed to determine value encoded in bar code; Data transmitted as binary codes to till / computer; These values are often sent as ASCII codes; For Camera / CCD System: Camera / CCD measures (ambient) light reflected from bar code; Camera / CCD converts light into an electrical signal; Light reflected back; Black areas reflect less light than white; Raw image data transmitted to computer; Image analysis software analyses image to determine value encoded in bar code;

Max 4

(b) Validate data entry//check bar code is valid/reasonable; Verify if bar code has been “input” accurately/correctly //check bar code not damaged / altered; R validate the item

Max 1

(c) Keyboard/Keypad/Touch screen/Concept Keyboard/Electronic Scales NE scales

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E1. Candidates found this question difficult. Many seemed to be under the misconception that barcodes or magnetic stripes are incorporated into RFID systems. Considering that this method of identifying items is so frequently used nowadays it is sad to see that so few candidates were aware of the technical aspects and had no idea of the principles of operation of RFID tags. Most candidates concentrated on the fact that it would trigger an alarm bell; this fact, however, did not gain credit. The reader near the exit sends a radio frequency wave which the antenna of the RFID tag in the book receives when it comes within range. This energises the tag and then the transponder in the tag sends a data signal that the reader receives. Candidates should be aware that the tag in the book does not continually send out a signal.

E2. Students generally scored very well when completing the table of different storage media. Students who dropped marks tended to place CD media into the 3GB row and therefore not appreciate fully the different storage capacities.

When describing the workings of a CD drive it was clear that the majority of students appreciate that it uses a laser to read and write the data. To secure two marks, however, students needed to differentiate between the power of the laser being used in the read and write processes. Students who clearly described the difference on the physical media to represent binary 0s and 1s picked up the mechanism mark. Weaker students provided answers along the line of, ‘pits store 0s and 1s,’ and did not distinguish between pits and lands. A minority of students continue to mix up optical and magnetic media and wrote about magnets being used to write or read data. A few students described needles being used to scratch data onto the disk perhaps remembering vinyl records.

Question part (c) was generally answered well with the majority of students securing at least one mark. The most common answer was along the lines of the CD becoming damaged or scratched. Students need to be aware, however, that to gain a second mark they need to identify a different point from the first. A CD becoming scratched and a CD becoming damaged are not different enough to secure two marks. Students who recognised that the file format might no longer be supported secured a mark. There was slight confusion for a few students who stated that a DVD drive would not be able to open a CD.

E3. A substantial number of students secured no marks for describing how a hard disk drive works even though this question has been asked in a similar way before. A lot of students were too vague in their answers and failed to use terminology correctly. Many students also seem to be of the view that hard disk drives use lasers and sometimes tape.

More able students gave in-depth answers which clearly talked about the media being magnetic and used terminology such as platters, tracks and sectors. Weaker students either tended to talk about lasers or just answered about the use of a hard-drive to store data rather than how it works.

It was pleasing to see how many students secured full marks for the calculation required in part (b). Those that worked up the units using 1024 multiples found it quite easy to then see that the final answer was 2048. Many students used multiples of 1000 and still secured marks with a final approximate answer of 2000. As the specification mentions storage capacities, this question asked students to show their understanding of how we can move from MB to GB and then to TB. For this particular question we accepted responses in which students assumed that 1000GB = 1TB as this assumption is made by many hard disk drive manufacturers which was the context of the question. Students should not assume that we will accept this simplification in future questions.

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As was to be expected, given the lack of understanding demonstrated by some students in question part (a), responses to (c) were mixed. Students mostly gained marks for discussing how the amount of tracks might have changed or identifying that there could be multiple platters. There was some confusion over the use of layers and this might link back to students thinking that lasers are used.

The majority of students managed to secure at least one mark when talking about the advantages that a solid-state drive might bring. The most common answers talked about data access being faster or considered the fact that a solid-state drive would be lighter and consume less power. Weaker answers did not give enough information and included vague observations such as ‘it is faster’. A few students commented on the fact that this kind of drive would be non-volatile, identifying another misunderstanding of magnetic hard-drives.

E4. The majority of students secured all marks for question part (a) as they correctly identified the input devices needed. It is to be noted that a few students did not know what a flatbed scanner is and used this as an answer for a part of (a) and then also scored poorly in part (b).

Students were asked to discuss the principles of operation for a flatbed scanner for part (b) and it was pleasing to see more students gaining marks than in previous papers. It is clear, however, that some students still do not understand the purpose of a flatbed scanner; answers ranged from using lasers (with the assumption that a scanner is a printer) to working with barcodes in a supermarket. It also appears that there is confusion as to the correct principle where light is reflected compared with light actually passing through the document to sensors on the other side. Students who secured full marks correctly identified the major parts of a flatbed scanner and could describe how a document would be scanned.

E5. This question was poorly answered, with many responses focusing on the relative merits of the two printer types rather than the principles by which they operate.

Candidates who scored well clearly understood the workings of a laser printer, but often still struggled to write about an inkjet printer. Candidates could score only 4 marks for describing one type of printer.

Whilst the principles of operation of a laser printer were better known, quite a few candidates wrote about the laser burning the image onto the paper. A few candidates also seemed to have the impression that a laser printer needs no ink/toner and therefore is more cost effective. The majority of candidates struggled to explain correctly the use of the drum inside a laser printer. It was common for candidates to believe that the toner went straight onto the paper rather than onto the drum first.

Given the widespread use of inkjet printers, it was surprising to see how many candidates could not explain how one worked. Candidates who gained marks generally mentioned the fact that they worked line by line. Good candidates described the squirting or firing of ink but weaker candidates used terms such as ‘place and drop’ and did not do enough to secure a mark. Most candidates who described the cartridge colours did manage to secure a mark for this, but it was still common to see wrong colours mentioned.

A few candidates did not attempt this question at all, whilst some provided only a few sentences for an 8 mark question.

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E6. Some candidates provided good descriptions of two differences between primary and secondary storage, but, the majority failed to score any marks and a significant number clearly had no idea what the terms meant. The most common acceptable response was that primary store was volatile whereas secondary store was non-volatile. Some candidates gave the opposing side of the same point for each response and were therefore only able to gain one mark.

It is not true that secondary storage is always external or removable; nor is it universally the case that secondary storage devices have a higher storage capacity than primary storage. A CD-ROM or flash memory device may well have a storage capacity smaller than the primary store in the computer in which it is being used. To ensure that credit is gained, candidates need to make sure that differences are universally true, not just true in some specific cases.

The level of detail in descriptions of the principles of operation of a hard disk drive was limited. Many candidates described characteristics such as typical capacities and uses rather than principles of operation. Most candidates expressed themselves fluently so the general quality of language was good. However, candidates often lost marks because they could not use technical terms such as sector or platter precisely. Many candidates used the term needle instead of read / write head. The most common misconception was that a laser was used to read / write data. Even candidates who described the medium as being magnetic sometimes referred to pits on the disk or the use of a laser.

E7. This question covered biometric properties and RFID use. It is a question that has not been asked before and this often showed in the answers offered. What the term biometric property means was frequently answered with ideas that were either not biometric or not unique, especially when the candidates attempted to answer the second part of the question in the first part of the answer. When asked to give an example of such a property many more gained credit – but there were still far too many that included ideas such as passport numbers or National Insurance numbers etc. When asked how the RFID tag could be read at an airport appeared to think the tag in the passport initiated the whole process rather than the reader. Some candidates seemed to be answering a question that was not asked by simply listing what data might be held on the tag.

E8. This question was often answered by describing the entire system including the database lookup and printing the till roll which was clearly not what the question was asking. Candidates should read the question carefully before starting to answer. The question was quite clear in that it asked about the bar code reader and even gave an end point to the process stating, “excluding the use of the check digit.” Many answers concerned general stock control and automatic ordering systems which are more of an ICT-type answer than one expected from Computing candidates. A good number of candidates thought that the reader played some role in the security system somehow switching off RFID tags in the goods that were being scanned. At the other extreme, there were also many answers gaining full marks for very cogent descriptions.

Part (b) was answered quite weakly and approximately 15% of candidates did not attempt to answer it at all. Where the question was answered it was often incorrect with candidates believing that the check digit was the whole of the printed number below the bar code and its purpose was to allow the cashier to enter the number if the bar code had not scanned correctly. The check digit is in fact used to validate the input of the bar code. The idea of deactivating RFID tags also appeared here quite often.

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