2021 BLSS Computing P1

BLS/PRELIM/2021/4E/COMP/7155/01 BOON LAY SECONDARY SCHOOL PRELIMINARY EXAMINATION 2021 Name CCA Subject : COMPUTING Paper No : 1 Subject Code : 7155/01 Level : SECONDARY FOUR EXPRESS Date/Day : 30th AUGUST 2021 / MONDAY Time : 1100 – 1300 Duration : 2 HOURS Candidates answer on the Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Before you start your exam, check that you have received the correct paper and the number of printed pages are correct. Write your name, index number, and CCA in the spaces at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs or rough working. Do not use staples, paper clips, glue or correction fluid. Approved calculators are allowed. Answer all questions. The number of marks is given in brackets [ ] at the end of each question or part question. You should show all your working. The total number of marks for this paper is 80.

2 BLS/PRELIM/2021/4E/COMP/7155/01 This document consists of 13 printed pages. 1 Digital systems make use of several different methods to store data. a (i) Explain what is meant by “hexadecimal digits”. …………………………….……………………………………………………………………… …………………………….…………………………………………………………………...[1] (ii) Describe two examples where a hexadecimal storage system would be preferred over a denary system. …………………………….……………………………………………………………………… …………………………….……………………………………………………………………… …………………………….…………………………………………………………………...[2] (iii) Justify the use of hexadecimal storage systems in one of your examples in a(ii). …………………………….……………………………………………………………………… …………………………….…………………………………………………………………...[1] b (i) The character Omega, “Ω” is represented by the binary number 11101010 in ASCII. Convert 11101010 into a denary number. Show your working. …………………………….…………………………………………………………………...[1]

3 BLS/PRELIM/2021/4E/COMP/7155/01 (ii) The character “j” is represented by the denary number 106 in ASCII. Describe a method to convert 106 into its hexadecimal representation. …………………………….……………………………………………………………………… …………………………….……………………………………………………………………… …………………………….……………………………………………………………………… …………………………….……………………………………………………………………… …………………………….…………………………………………………………………...[3] 2 a Where appropriate, draw a line to match the terms to its correct description. Terms Description DoS attack Cookie A small piece of data used by websites to store personal information on a user’s web browser. Encryption Hidden program that secretly collects personal information. Phishing Flooding network with useless traffic, making the network slow or inaccessible. Software piracy Sending fake or spoof emails.

4 BLS/PRELIM/2021/4E/COMP/7155/01 Worms [4] b (i) What are cybersecurity threats and how can they affect our data security? …………………………….……………………………………………………………………… …………………………….……………………………………………………………………… …………………………….…………………………………………………………………...[2] (ii) In the context of computer systems, explain the difference between a computer worm, and a computer virus. …………………………….……………………………………………………………………… …………………………….…………………………………………………………………...[2] (iii) A key-logger is software that records every keystroke that has been entered into a computer system. Explain how a key-logger can be used as a part of a system’s security, or as spyware. As a part of a system’s security …………………………….……………………………………………………………………… …………………………….……………………………………………………………………… …………………………….…………………………………………………………………...[2] As a spyware …………………………….……………………………………………………………………… …………………………….……………………………………………………………………… …………………………….…………………………………………………………………...[2]

5 BLS/PRELIM/2021/4E/COMP/7155/01 (c) (i) What is ‘software piracy’? …………………………….……………………………………………………………………… …………………………….…………………………………………………………………...[1] (ii) Provide two possible reasons that causes software piracy to occur. …………………………….……………………………………………………………………… …………………………….……………………………………………………………………… …………………………….…………………………………………………………………...[2] (iii) Describe possible positive and negative effects of software piracy on the software industry. Positive …………………………….……………………………………………………………………… …………………………….…………………………………………………………………...[1] Negative …………………………….……………………………………………………………………… …………………………….…………………………………………………………………...[1] 3 a Decomposition, Pattern Recognition and Generalisation are three common problem solving techniques. (i) Describe how decomposition helps in problem-solving and algorithm design. …………………………….……………………………………………………………………… …………………………….…………………………………………………………………...[1] (ii) One approach to decomposing is modularity. Describe what this is.

6 BLS/PRELIM/2021/4E/COMP/7155/01 …………………………….……………………………………………………………………… …………………………….…………………………………………………………………...[1] (iii) What is Pattern Recognition? How is it useful in solving problems? …………………………….……………………………………………………………………… …………………………….……………………………………………………………………… …………………………….…………………………………………………………………...[2] b Read the following lines of code. 1 string_1 = 'this is a string 1234AZ!@#$%' 2 count = 0 3 for i in range(len(string_1)): 4 if string_1[i].isalpha(): count += 1 5 print(count) (i) What is the function of this code? …………………………….……………………………………………………………………… …………………………….…………………………………………………………………...[1] (ii) Explain how this code can be used for other similar situations with minimal modifications. …………………………….……………………………………………………………………… …………………………….……………………………………………………………………… …………………………….…………………………………………………………………...[2] (iii) In the code provided, suggest a replacement for the variable name count that is more self-explanatory. …………………………….……………………………………………………………………… …………………………….…………………………………………………………………...[1]

7 BLS/PRELIM/2021/4E/COMP/7155/01 4 a (i) Besides magnetic storage devices, there are two other types of external storage technologies found in a computer system. List their corresponding example and describe each of them in terms of their advantage and disadvantage. Type 1: Optical Storage Example: ………………………………………………………………………………………… Advantage: ……………………………………………………………………………………… Disadvantage: ………………………………………………………………………………..[3] Type 2: Solid-State Storage Example: ………………………………………………………………………………………… Advantage: ……………………………………………………………………………………… Disadvantage: ………………………………………………………………………………..[3] (ii) State what RAM stands for, and explain how it differs from Read Only Memory. …………………………….……………………………………………………………………… …………………………….……………………………………………………………………… …………………………….…………………………………………………………………...[2] b Explain the difference between an address bus and a data bus in a computer. …………………………….……………………………………………………………………… ………………..………………….…………………………………………………………………....... ………………..………………….…………………………………………………………………...[2]

8 BLS/PRELIM/2021/4E/COMP/7155/01 5 a In the space below, construct the logic circuit diagram for the following Boolean statement. X = (A OR B) NAND ((NOT A) AND C)) [4] b Construct the truth table for the Boolean statement: X = (A OR B) NAND ((NOT A) AND C)) A B C 0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 A – B – C – – X

9 BLS/PRELIM/2021/4E/COMP/7155/01 1 1 1 [4] 6 a (i) Suggest why a network of computing devices (computers, laptops, handphones, printers) could be useful at home. …………………………….……………………………………………………………………… …………………………….…………………………………………………………………...[1] (ii) Suggest how the setup of a home network compares to the computer network in a school computer lab in terms of : Data access control …………………………….……………………………………………………………………… …………………………….………………………………………………………………