2021 MSHS Computing P1 Solutions

Class/ Index Number / Centre Number/ ‘O’ Level Index Number / Name MARIS STELLA HIGH SCHOOL PRELIMINARY EXAMINATION SECONDARY FOUR COMPUTING 7155 Paper 1 Written 25 August 2021 2 hours Candidates answer on the Question Paper No Additional Materials are required. READ THESE INSTRUCTIONS FIRST MARK SCHEME For Examiner’s Use 80

2 This document consists of 10 printed pages. 1 Xavier is concerned about security threats that he may encounter when using the Internet. Two of the threats that he is concerned about are phishing and pharming. (a) Give one similarity and two differences between phishing and pharming. [3] One mark for similarity Similarity - Both involve fake/fraudulent websites - Both are designed to steal personal data Two marks for difference Difference - Pharming requires the installation of malicious code installed on computers - Phishing is initiated/started using form of an email - Phishing requires user to click on a link / open an attachment (b) State two other threats that Xavier could encounter when using the Internet. [2] Two marks - Virus - Worm - Malware (c) Xavier uses a firewall to secure data on his computer. (i) Xavier tells his classmate that a firewall can only be software-based. Explain if you agree or disagree with him. A firewall can be both a software and hardware. I disagree with Xavier. [1] (ii) Describe how the firewall helps to keep Xavier’s data secured. [4] Any four from: - Help prevent hacking / unauthorised access - Monitor incoming and outgoing traffic - Allows setting of criteria / rules for traffic - Can check whether traffic meets / defies criteria rules - Can reject any traffic that does not meet / defies criteria

3 2 A paragraph is given about MAC addresses and IP addresses. Complete the paragraph using the list of terms given. Not all terms need to be used. compiled control identify principal similar computer dynamic packet protocol unique [5] One mark for each correct term in the correct place - control - unique - identify - protocol - dynamic 3 (a) Five statements are given about storage devices. Tick (P) to show if the statement applies to hard disk drive (HDD) storage or solid state drive (SSD) storage. Some statements can apply to both. [5] Statement HDD (P) SSD (P) It uses magnetic properties to store data P It is non-volatile storage P P It can be used as an external storage device to back up data P P It has moving parts P It uses flash memory to store data P (b) Optical storage is another type of storage. [2] Any two from - CD (drive) - DVD (drive) - Blu-ray (drive)

4 4. Joshua wants to create a simple game using the programming language he is learning. (a) In the single-player computer game, the player has to shift brown blocks in order to create a clear path for the red block to reach the exit. The blocks can only move in either up and down directions or left and right directions. When the player successfully drags the red block to the exit sign, a message “Level Cleared” is shown and the next puzzle is unlocked. Players are given the choice to start from the last puzzle, choose a previously played puzzle or clear all current records and restart from the first puzzle. Before the program is written, the problem is decomposed into smaller, more manageable parts. Identify and describe three of these smaller parts. [3] Any three from - Menu to select if the player wants to start a new record, load his last unlocked puzzle, or select puzzles previously unlocked - Puzzles module to place (in a fixed sequence) different puzzle configurations for players to play - Winning module to detect if the red block is place at the exit sign to trigger the “Level Clear” message and to unlock the next puzzle. (b) In the process of creating the game, Joshua makes several programming errors. A logic error is one type of program error. Identify and describe two other types of program error. [4] Syntax Error - Errors that causes the translation process from source code to machine code to fail Run Time Error - Errors that occur while a program is running, usually causing the program to crash or hang

5 5 (a) Name and draw the single logic gate that can replace the given logic circuits. (i) NAND gate (ii) NOR gate [2] [2] (b) Complete the truth table for the given logic statement: X = (((A OR C) AND (NOT A AND NOT C)) NOR B) A B C Working space X A OR C NOTA AND NOT C NOT A AND NOT C NOR B 0 0 0 0 1 0 0 0 0 1 1 0 1 1 0 1 0 0 1 0 0 0 1 1 1 0 0 0 1 0 0 1 0 1 1 1 0 1 1 0 1 1 1 1 0 1 0 0 0 1 1 1 1 0 0 0 [4] 6 (a) An algorithm has been written in pseudocode to input the names and marks of 35 students. The algorithm stores the names and marks in two arrays name[] and mark[]. The highest mark awarded is calculated and the number of students with that mark is counted. Both of these values are output. 01 highestmark = 100 02 highestmarkstudents = 0 03 FOR count = 0 to 34 04 OUTPUT “ Please enter student name: ” 05 INPUT name[count] 06 OUTPUT “Please enter student mark: ” 07 INPUT mark[counter] 08 IF mark[count] == highestmark 09 highestmarkstudents = highestmarkstudents - 1 10 ENDIF 11 IF mark[count] > highestmark 12 mark[count] = highestmark 13 highestmarkstudents = 1 14 ENDIF 15 NEXT 16 OUTPUT “There are ”, highestmarkstudents, “ with the highest mark of ”, highestmark

6 State the line number in the algorithm where the four errors are found. Suggest a correction for each error. [4] Line 1 highestmark = 0 Line 7 INPUT mark[count] Line 9 highestmarkstudents=highestmarkstudents+1 Line 12 highestmark = mark[count] (b) Explain how you could extend the algorithm to also find the lowest mark awarded, count the number of students with that mark, and output both these values. [6] Any Six from - Add variable lowestmark … - … Set this to a high value for example 100 - Add variable lowestmarkstudents … - … Set this to zero - Add check IF mark[count] == lowestmark … - If check is true, add1 to lowestmarkstudents - Add check IF mark[count] < lowestmark - If check is true, set lowestmark to mark[count] and lowestmarkstudents to 1 - Add extra output statements

7 7 This pseudocode represents an algorithm. flag = -1 WHILE flag != 0 flag = 0 FOR count = 0 to 3 IF num[count] < num[count + 1] store = num[count] num[count] = num[count+1] num[count+1] = store flag = 1 ENDIF NEXT ENDWHILE (a) The contents of the array at the start of the algorithm are: num[0] num[1] num[2] num[3] num[4] 45 56 30 12 15 Complete the trace table for the algorithm using the data given in the array. flag count num[0] num[1] num[2] num[3] num[4] store -1 45 56 30 12 15 0 0 45 56 45 1 1 2 3 12 15 12 0 0 1 2 3 1m 1m 1m 1m 1m [5] (b) Describe the purpose of the algorithm. Any two from - The algorithm sorts/orders numbers - … into descending order / from largest to smallest

8 8 Range check is an example of how programs can perform validation checks on data entered. (a) Give the names of two other different validation checks and state the purpose of each. [4] One mark for correct validation and