AQA A-level COMPUTER SCIENCE

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Materials For this paper you must have: • a calculator. Instructions • Use black ink or black ball-point pen. • Fill in the boxes at the top of this page. • Answer all questions. • Yo... u must answer the questions in the spaces provided. Do not write outside the box around each page or on blank pages. • If you need extra space for your answer(s), use the lined pages at the end of this book. Write the question number against your answer(s). • Do all rough work in this book. Cross through any work you do not want to be marked. Information • The marks for questions are shown in brackets. • The maximum mark for this paper is 100. Advice • In some questions you are required to indicate your answer by completely shading a lozenge alongside the appropriate answer as shown. • If you want to change your answer you must cross out your original answer as shown. • If you wish to return to an answer previously crossed out, ring the answer you now wish to select as shown. Please write clearly in block capitals. Centre number Candidate number Surname Forename(s) Candidate signature I declare this is my own work. A-level COMPUTER SCIENCE Paper 2 2 *02* IB/G/Jun22/7517/2 Do not write outside the box 3 Answer all questions. 0 1 . 1 Describe how a 12-bit unsigned binary integer such as 010010101110 can be converted directly into hexadecimal. The method you describe must not involve converting into decimal. [2 marks] 0 1 . 2 State one reason why hexadecimal is often used in preference to binary. [1 mark] 0 2 . 1 A data communications system uses parallel data transmission. Describe how parallel data transmission works. [2 marks] 3 *03* Turn over ► IB/G/Jun22/7517/2 Do not write outside the box 6 0 2 . 2 State one advantage of serial data transmission over parallel data transmission. [1 mark] 0 2 . 3 Shade one lozenge to indicate which of these statements about data communications systems is false. [1 mark] A For a particular communications channel, the bit rate can be higher than the baud rate. B Latency is the rate at which signals on a wire or line can change. C The bandwidth of a transmission medium is the range of signal frequencies that the medium can transmit without a significant reduction in signal strength. D The greater the bandwidth of a transmission medium the higher the bit rate that can be achieved by a communication system using it. 0 2 . 4 State the purpose of the start bit in asynchronous serial transmission. [1 mark] 0 2 . 5 State the purpose of the stop bit in asynchronous serial transmission. [1 mark] 4 *04* IB/G/Jun22/7517/2 Do not write outside the box 0 3 . 1 Complete the truth table in Figure 1 for the inputs A and B. [1 mark] Figure 1 ?? ?? ?? + ?? ??� ??� ??� ∙ ??� ?? � ��� ∙ �� ??�� 0 0 0 1 1 0 1 1 0 3 . 2 The truth table in Figure 1 demonstrates the correctness of an important law in Boolean algebra. State the name of the law. [1 mark] 5 *05* Turn over ► IB/G/Jun22/7517/2 Do not write outside the box 6 0 3 . 3 Using the rules of Boolean algebra, simplify the following Boolean expression. � A��� + B ������ ∙ � C + B �������� ⋅ �� C�� + C ⋅ (A + A� ∙ (B + 1)) You must show your working. [4 marks] Working Answer Turn over for the next question 6 *06* IB/G/Jun22/7517/2 Do not write outside the box 4 0 4 . 1 Define the term ‘system software’. [1 mark] 0 4 . 2 The list below contains five types of software. Four of the types are examples of system software. Shade one lozenge to indicate which type of software is not system software. [1 mark] A Assemblers B Bitmap image editors C Interpreters D Libraries E Utility programs 0 4 . 3 Describe two functions of an operating system. [2 marks] Function 1 Function 2 7 *07* Turn over ► IB/G/Jun22/7517/2 Do not write outside the box 0 5 . 1 Figure 2 shows a number stored using a fixed point representation and two’s complement, with six bits before and four bits after the binary point. Figure 2 1 0 1 1 0 0 1 0 1 1 Convert the number in Figure 2 to decimal. You should show your working. [2 marks] Answer 0 5 . 2 State two reasons why values stored using a floating point representation are usually stored in normalised form. [2 marks] Reason 1 Reason 2 Question 5 continues on the next page 8 *08* IB/G/Jun22/7517/2 Do not write outside the Questions 05.3 box , 05.4 and 05.5 use a normalised floating point representation with an 8-bit mantissa and a 4-bit exponent, both stored using two’s complement. 0 5 . 3 Figure 3 shows a floating point representation of a number. Figure 3 Calculate the decimal equivalent of the number. Express your answer as a fraction or to 4 decimal places. You should show your working. [2 marks] Answer 9 *09* Turn over ► IB/G/Jun22/7517/2 Do not write outside the Questions 05.3, 05.4 and 05.5 use a normalised floating point representation with an box 8-bit mantissa and a 4-bit exponent, both stored using two’s complement. 0 5 . 4 Write the normalised floating point representation of the decimal value –23.25 in the boxes below. You should show your working. [3 marks] Answer Question 5 continues on the next page 10 *10* IB/G/Jun22/7517/2 Do not write outside the box 11 Questions 05.3, 05.4 and 05.5 use a normalised floating point representation with an 8-bit mantissa and a 4-bit exponent, both stored using two’s complement. 0 5 . 5 Figure 4 shows the closest possible representation of the decimal number –0.22558594 in this floating point system. Figure 4 By converting this number back to decimal it can be seen that the actual value stored is –0.2265625 Calculate the relative error that has occurred when representing –0.22558594 You should show your working. Express your answer as a percentage to 2 decimal places. [2 marks] Answer 11 *11* Turn over ► IB/G/Jun22/7517/2 Do not write outside the Turn over for the next question box DO NOT WRITE ON THIS PAGE ANSWER IN THE SPACES PROVIDED 12 *12* IB/G/Jun22/7517/2 Do not write outside the box 0 6 Supermarkets often gather information about their customers and the purchases that they make. This information can be analysed by the supermarket and other companies for a range of purposes. Some of the information is collected at the checkout, where the identity of the person is read from a loyalty or payment card using RFID (radio-frequency identification) and a barcode reader is used to identify the products being purchased. By analysing the purchases that a shopper has made, it might be possible to identify such things as whether the shopper has children, is pregnant, or lives in a house with a garden. Other types of analysis might include the amount of money a customer spends, the times that they choose to shop at and the differences in shopping habits of different groups of shoppers. Describe the principles of operation of the hardware used to collect the information and discuss some of the ethical and legal issues that might arise as a result of the capture and processing of this data. In your answer you will be assessed on your ability to follow a line of reasoning to produce a coherent, relevant and structured response. [12 marks] 13 *13* Turn over ► IB/G/Jun22/7517/2 Do not write outside the box 12 14 *14* IB/G/Jun22/7517/2 Do not write outside the box 0 7 A network of zoos uses a relational database system to store information about the animals that they have so that they can be matched up with animals at other zoos in a breeding programme. Figure 5 shows the structure of the relations in the database. Figure 5 Zoo(ZooName, Town, Country) AnimalLocation(AnimalID, ZooName, DateArrived, DateLeft) Animal(AnimalID, IndividualName, Species, DateOfBirth, Sex) Match(AnimalFemaleID, AnimalMaleID, DateOfMatch, Successful) • The Zoo relation stores details of the zoos that participate in the breeding programme. Each zoo is uniquely identified by its ZooName. • The AnimalLocation relation identifies which zoos each animal has lived at. The zoo that the animal is currently at can be identified because the DateLeft attribute is set to 01/01/0001 to indicate that the animal has not left. • The Animal relation stores details of the individual animals that are available to be matched with other animals for breeding. Each animal is identified by a unique number, the AnimalID. The individual name of the animal (eg ‘Timothy’) is also stored, together with the species of the animal (eg ‘Red Panda’), its date of birth and its sex (‘Male’ or ‘Female’). • The Match relation stores details of matches that have been made. The attributes AnimalFemaleID and AnimalMaleID refer to the AnimalID values of the two matched animals in the Animal relation. 0 7 . 1 Shade one lozenge to identify which of the properties below does not have to be true for a fully normalised database. [1 mark] A Each attribute in a relation is dependent on the primary key. B Each attribute in a relation is dependent only on the primary [Show More]

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