N04/5/COMSC/SP1/ENG/TZ0/XX COMPUTER SCIENCE STANDARD LEVEL PAPER 1. Monday 15 November 2004 (afternoon) 1 hour 15 minutes INSTRUCTIONS TO CANDIDATES

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1 c IB COMPUTER SCIENCE STANDARD LEVEL PAPER 1 DIPLOMA PROGRAMME PROGRAMME DU DIPLÔME DU BI PROGRAMA DEL DIPLOMA DEL BI N04/5/COMSC/SP1/ENG/TZ0/XX Monday 15 November 2004 (afternoon) 1 hour 15 minutes INSTRUCTIONS TO CANDIDATES! Do not open this examination paper until instructed to do so.! Section A: answer all the questions.! Section B: answer three questions pages

2 2 N04/5/COMSC/SP1/ENG/TZ0/XX SECTION A Answer all the questions. 1. Three optical input systems for computers are OMR (Optical Mark Recognition), OCR (Optical Character Recognition) and Bar-Codes. State which is most appropriate for inputting data recorded by a human being: OMR, OCR, or Bar-Codes. State which is most appropriate for producing a document for further word-processing. Describe how one of these systems is commonly used at a point-of-sale in a retail store. 2. Two search algorithms are binary search and sequential search. Outline a set of data, stored in an array, for which a binary search cannot be used. This must include at least four sample data items, and clearly state the reason that a binary search cannot be used. State which search algorithm (binary or sequential) is more efficient on large sets of data in the situation where either can be used. 3. The following algorithm is supposed to return the last digit of an integer. For example: LASTDIGIT(12345) ==> 5 LASTDIGIT(3) ==> 3 function LASTDIGIT(val NUMBER integer) result integer while (NUMBER >= 10) do NUMBER <-- NUMBER - 10 endwhile return NUMBER endfunction LASTDIGIT Determine the value returned by the function for a negative input: LASTDIGIT ( -27 ) The value returned for LASTDIGIT ( -27) is incorrect. State whether this is a syntax error, a logic error, a run-time error, or none of these. Explain why the use of a compiler rather than an interpreter can reduce the number and severity of run-time errors

3 3 N04/5/COMSC/SP1/ENG/TZ0/XX 4. A teacher stores graphics files on a server in a LAN. A student stores graphics files on a web-server. Outline one advantage and one disadvantage of LAN storage compared to WAN storage. Describe a reliable method the teacher could use to copy files from one LAN to a separate LAN which is not connected to the Internet. [4 marks] 5. A multimedia software utility retrieves data from a hard-disk at a speed of 5 MB per second. Calculate the data-transfer rate in kb per second. State whether digital-to-analog conversion is performed by multimedia software, a hardware device, or the operating system. 6. A printer uses parity checking during data transmission. Describe how parity checking is performed. Include some sample data in your answer. State whether it is possible for a printer to be infected by a computer virus, and justify your answer. [3 marks] 7. Describe one application of sensors. Explain why the signal from a sensor requires conversion before processing in a computer Turn over

4 4 N04/5/COMSC/SP1/ENG/TZ0/XX SECTION B Answer three questions. 8. An server must store the NAME, ACCOUNT, and PASSWORD for each user in the database. The database is represented by three parallel arrays as shown below. There are exactly four users in the system. NAME Fred Green Elly Brown Dave Black Axel White ACCOUNT GreenF@mail.com BrownE@mail.com BlackD@mail.com WhiteA@mail.com PASSWORD Tree Earth Moon Sun The following algorithm should sort the data. It assumes all 3 arrays have already been declared as global variables, and already contain 4 rows of data. main SORTDATA SORT(NAME) endmain SORTDATA procedure SORT(ref DATA string array[1..4]) declare P integer, C integer, B integer for P <-- 1 upto 3 do B <-- P for C <-- P+1 upto 4 do if (DATA[C] < DATA[B]) then B <-- C endif endfor SWAP( DATA[B],DATA[P] ) endfor endprocedure SORT procedure SWAP( ref ITEMA string, ref ITEMB string) declare TEMP string TEMP <-- ITEMA ITEMA <-- ITEMB ITEMB <-- TEMP endprocedure SWAP State the name of the standard sorting algorithm attempted by SORT. (This question continues on the following page)

5 5 N04/5/COMSC/SP1/ENG/TZ0/XX (Question 8 continued) Trace the algorithm, using the array given, and state the contents of the NAME array after the second pass - that is, after the loop where P = 2. [3 marks] Outline the difference between pass-by-value and pass-by-reference parameters. The algorithm does not correctly sort the database. (d) (i) Describe the incorrect results of this error and the cause of the error. (ii) Suggest a change to the SORT algorithm, which would correct this error. The correction must only change the SORT procedure, and should not change the SWAP procedure Turn over

6 6 N04/5/COMSC/SP1/ENG/TZ0/XX 9. A book publisher is converting all of its books to electronic (digital) versions. Each book is scanned in through an optical scanner. The text is converted to HTML format. Pictures are automatically saved in a standard graphics format and linked to the HTML text in the correct position. The resulting digital books can be displayed by a browser. A clerk must place a book in the scanner, press a button, turn a page, place it in the scanner again, press a button again, etc. This continues through the entire book. State whether the scanning process is best described as batch processing, interactive processing, or real-time processing. Explain the need for analog-to-digital conversion during the scanning process. Discuss an appropriate testing-strategy for three aspects of the conversion process from paper to electronic format. [3 marks] After converting a book to HTML format, the publisher may add multimedia files to the book, creating a multimedia enhanced version. The average size of a multi-media enhanced version is 500 MB. (d) Explain how a web-browser can display a 500 MB book in a computer with only 64 MB of RAM. The publisher sells some multimedia enhanced versions on CD-ROM - these are identical to the online versions. Although the publisher's web-site is always available, and the online books are available at no cost, they still sell a lot of CD-ROMs. (e) Outline two advantages of using the CD-ROM version rather than the web-based version, justifying the cost of purchasing the CD-ROM

7 7 N04/5/COMSC/SP1/ENG/TZ0/XX 10. A software developer is creating an Electronic Voting Application (EVA). EVA can be used in public elections. It might be used through Internet connections or on PCs in normal voting locations. The hardware issues have been solved, but the software is still under development. There are three major undecided issues: 1. Interface - How can users conveniently interact with the system? 2. Security - How can cheating (fraud) be prevented? 3. Reliability - How can operators ensure that all votes are correctly counted and the system never loses data? (d) Outline two standard methods for collecting wishes and preferences from users about the design of the interface. Explain how reliability can be improved by clear and complete system documentation. State which of the three undecided issues might be handled partially through encryption, and justify your answer. In an election with eight candidates, a voter must vote for exactly one candidate. (i) (ii) (iii) State whether validation or verification is appropriate for ensuring that the voter only votes for one candidate. Outline one appropriate response from the system when a voter incorrectly votes for two candidates. Suggest a method for storing each voter's ballot in a single byte Turn over

8 8 N04/5/COMSC/SP1/ENG/TZ0/XX 11. Alex is a personal computer (PC) user. She uses her PC for: 1. Playing video games (stored locally) 2. Internet access, especially downloading files 3. Word-processing simple text documents Alex's PC is 5 years old. The hard-disk is about half full, which is okay, but Alex finds that all the applications listed above run too slowly. She wishes to upgrade the hardware, by doing one or more of the following:! Add an extra hard-disk-drive! Add more RAM! Replace the CPU with a faster model (d) Explain why adding more RAM might speed up one of the applications, clearly identifying which application you are discussing. Explain why replacing the CPU will probably not speed up Internet downloads. Explain why none of the upgrades listed is likely to speed up word-processing. One possible CPU upgrade would significantly increase the cache memory, but this new CPU runs at the same speed as the old one. Outline the function of cache memory, and state whether or not it is possible that this upgrade would speed up the applications. [3 marks] Alex found out that hardware upgrades are expensive, and is looking for ways to speed up the applications without hardware upgrades. (e) State the name of a software utility which might speed some of the applications (above), and outline how this software utility functions

M12/5/COMSC/SP1/ENG/TZ0/XX COMPUTER SCIENCE STANDARD LEVEL PAPER 1. Friday 18 May 2012 (afternoon) 1 hour 30 minutes INSTRUCTIONS TO CANDIDATES

M12/5/COMSC/SP1/ENG/TZ0/XX COMPUTER SCIENCE STANDARD LEVEL PAPER 1. Friday 18 May 2012 (afternoon) 1 hour 30 minutes INSTRUCTIONS TO CANDIDATES M12/5/COMSC/SP1/ENG/TZ0/XX 22127013 COMPUTER SCIENCE STANDARD LEVEL PAPER 1 Friday 18 May 2012 (afternoon) 1 hour 30 minutes INSTRUCTIONS TO CANDIDATES Do not open this examination paper until instructed