Computer Science > QUESTION PAPER & MARK SCHEME > OCR A Level Computer Science H446/01 Computer Systems. QUESTION PAPER AND ANSWERS (All)

OCR A Level Computer Science H446/01 Computer Systems. QUESTION PAPER AND ANSWERS

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OCR Insurance uses a computer system to calculate the price that customers pay for car insurance. (a) The computer system contains a CPU, GPU, RAM and ROM. (i) State two factors that affect the performance of a CPU. 1 ........................................................................................................................................ ........................................................................................................................................... 2 ........................................................................................................................................ ........................................................................................................................................... [2] (ii) Explain the difference between RAM and ROM, including how these are used by the computer system. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [4] (iii) Describe one non-graphical use OCR Insurance may have for a GPU. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2] 3 © OCR 2021 Turn over (b) The CPU uses pipelining to improve efficiency. Explain what is meant by the term ‘pipelining’. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [3] 4 © OCR 2021 (c)* OCR Insurance’s computer system uses secondary storage across the company in servers, client machines and for backup purposes. For each of these, discuss whether magnetic storage or solid state storage would be most suitable, taking into account the advantages and disadvantages of both. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [9] 5 © OCR 2021 Turn over (d) Customers’ details are stored in the flat file database table Customer. An extract of the table is shown below. CustomerID Surname Title Phone CarReg JJ178 James Mr (0121) 343223 DY51 KKY HG876 Habbick Miss (01782) 659234 PG62 CRG EV343 Elise Mrs (07834) 123998 HN59 GFR PG127 Pleston Mr (07432) 234543 JB67 DSF (i) State what is meant by the term ‘primary key’, identifying the primary key in the table above. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2] (ii) Write the SQL statement that would show only the CustomerID and Surname fields for customers with the Title “Miss” or “Mrs”. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [4] (iii) Describe one problem that would arise with the flat file database structure if a customer wanted to insure more than one car at the same time. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2] 6 © OCR 2021 (iv) Describe how the flat file database structure could be altered to efficiently allow each customer to insure multiple cars at the same time. (You may assume each car is insured to only one customer.) ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [5] 7 © OCR 2021 Turn over 2 (a) (i) Convert the denary number 231 to an unsigned 8-bit binary number. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [1] (ii) Convert the hexadecimal number 6F to an unsigned 8-bit binary number. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [1] (b) The floating point number 0011010100 is stored using 6 bits for the mantissa and 4 bits for the exponent, both in two’s complement. This number is not normalised. (i) Give the normalised version of this number, showing your working. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [4] 8 © OCR 2021 (ii) Convert your answer to part (i) to denary, showing your working. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [3] (c) Add together the two numbers below. Both numbers are stored in normalised floating point format, using 6 bits for their mantissa and 4 bits for their exponent which are both in two’s complement. Show the result in the same format and show your working. 0110000110 + 0101000100 ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [5] 9 © OCR 2021 Turn over 3 A website sells tickets for sporting events. The website uses HTML, CSS and JavaScript. (a) Describe the purpose of HTML and CSS within the code of the website. HTML ........................................................................................................................................ ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... CSS .......................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... [4] (b) One page in the website contains a hyperlink on an image. When the image stored as “ticket.png” is clicked, the user is hyperlinked to the page stored as “booking.htm”. Write the HTML code to implement this hyperlink. ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [3] 10 © OCR 2021 The website charges a booking fee of £2.99 on each ticket sold. In addition, if the tickets are purchased from outside of the UK, £4.99 is added to the booking fee. The booking fee is calculated using a JavaScript function named bookingfee(). (c) Complete the definition of the bookingfee() function below. function bookingfee(numtickets, country) { var nonUKprice = 4.99; var perTicketPrice = ………………………………………; var total = 0; if (country!="UK") { total = total + ………………………………………; } total = total + (……………………………………… * perTicketPrice); ……………………………………… total; } [4] (d) The JavaScript function above is used to show users the booking fee. When users click to buy the tickets, the booking fee is calculated again on the server. (i) Explain why server side processing is used to recalculate the booking fee. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [3] (ii) Explain one advantage of client side processing to either the customer buying the tickets, or to company who own the website. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2] 11 © OCR 2021 Turn over (e) Users are able to search for and find the ticket website using a search engine. Search engines can use indexing and ranking. (i) Describe how a website is indexed by a search engine. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [4] A search engine can use the PageRank algorithm to determine a website’s ranking. The PageRank algorithm utilises a damping factor. (ii) State what is meant by the term ‘damping factor’. ........................................................................................................................................... ...................................................................................................................................... [1] (iii) Give two other factors that affect the output value given by the PageRank algorithm for a website. 1 ........................................................................................................................................ ........................................................................................................................................... 2 ........................................................................................................................................ ........................................................................................................................................... [2] 12 © OCR 2021 4* “The Computer Misuse Act means that computer users are criminalised for simply trying to learn how systems work.” Discuss whether or not you agree with this statement. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... ..................................................................................................................................................... [9] 13 © OCR 2021 Turn over 5 All users of a computer system have a unique username and password. The computer system has implemented two-factor authentication so that users must respond to either an email or text message containing a secret code to be able to access the system. Let: A be a Boolean value for if a user enters a valid username B be a Boolean value for if a user enters a password that matches their username C be a Boolean value for if a user is able to respond to an email containing a secret code D be a Boolean value for if a user is able to respond to a text message containing a secret code Q be a Boolean value for if entry to the computer system is allowed (a) Complete the Boolean expression below: Q ≡ .................................................................................................................................... [3] (b) Another Boolean expression for a logic system is shown below: Q ≡ ¬ (¬ A ∧ ¬ B) (i) Simplify this Boolean expression so that it does not include any negation. You must explain which Boolean algebra rule(s) you are using at each step. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2] 14 © OCR 2021 A B S C (c) The logic circuit above has two inputs (A, B) and two outputs (S, C). (i) Give the Boolean expressions for the outputs S and C. S ≡................................................................................................................................... C ≡................................................................................................................................... [2] (ii) Complete the truth table for this logic circuit. A B S C 0 0 0 1 1 0 1 1 [2] (iii) Describe how this logic circuit can be adapted to add together two 4-bit binary numbers. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [4] 15 © OCR 2021 Turn over BLANK PAGE PLEASE DO NOT WRITE ON THIS PAGE 16 © OCR 2021 6 A program written using the Little Man Computer instruction set is shown in Fig. 1. INP STA numone INP STA numtwo main LDA numone SUB numtwo BRP pos notpos LDA count OUT LDA numone OUT HLT pos STA numone LDA count ADD one STA count BRA main numone DAT numtwo DAT one DAT 1 count DAT 0 Fig. 1 (a) Various registers are used when the program above is executed. (i) State what is meant by the term ‘register’. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2] (ii) Explain how the accumulator is used when the line BRP pos is executed. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2] 17 © OCR 2021 Turn over (b) Complete the table below to show the output(s) from this program given the inputs. Inputs Output(s) 12, 5 18, 2 16, 4 3, 7 [4] (c) Write an algorithm using pseudocode that has the same functionality as the code in Fig. 1. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [4] 18 © OCR 2021 (d)* In assembly language, different modes of addressing memory can be used. Discuss the different modes used. You should include: • How the operand value is determined • What an operand of 27 would refer to in that mode • The reasons for requiring multiple modes of addressing [12] ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ...............................................................................................

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