MSHS 2019 P1 Solution

Class Index Number Name MARIS STELLA HIGH SCHOOL PRELIMINARY EXAMINATION SECONDARY FOUR COMPUTING 7155/01 Paper 1 Written 28 Aug 2019 2 hours Candidates answer on the Question Paper. No Additional Materials are required. MARK SCHEME For Examiner’s Use This document consists of 13 printed pages. 80

2 1 Insert six of the following words or numbers about computers and data in the correct place in the text below. 2 10 16 analogue binary denary digital hexadecimal While analogue data is transmitted via fibre optical cables, a computer cannot process this type of data. For a computer to be able to process data, it needs to be converted to digital data. As humans, we mostly use a denary number system; this is a base 10 number system. Computers use a binary number system; this is a base 2 number system. [6] 2 The three binary numbers in the registers X, Y, Z were transmitted from one computer to another. Parity bit Register X 1 0 0 1 1 0 0 0 Register Y 0 1 1 0 0 1 1 1 Register Z 1 0 0 1 1 0 0 1 One binary number was transmitted incorrectly. This is identified through the use of a parity bit. Identify which register contains the binary number that was transmitted incorrectly. Explain the reasons for your choice. Any three from: - Count the number of 1/0 bits (in each byte/register) - Two bytes/registers have an odd number of 1/0 bits // Two use odd parity - Odd parity must be the parity used - One byte/register has an even number of 1/0 bits // One uses even parity - One with an even number of one bits/even parity is incorrect// Register Z should be odd parity [4] 3 John is writing a program using a high-level language. The program will be published and sold for a profit.

3 (a) John uses an interpreter when creating the computer program. State three features of an interpreter. [3] (b) James writes a similar code and compiled the program when he completed it. Explain two benefits of compiling the program. [4] (a) Any three from: - Executes one line at a time // translates source code line by line - Produces error message to tell user location of error // easier to debug code - Stops execution once the program encounters an errors - Changes to the source code take effect immediately - Interpreters usually offer an interactive mode, which facilitates learning and experimentation. (b) Any four from: - Produce executable file… - … more saleable - Program will be machine independent/portable… - … this means it can be used on any hardware - No need for compiler to run executable file… - … this means it will be quicker to run - … customers can just execute the program - Source code cannot be accessed… - … therefore, code cannot be stolen/plagiarised 4 Consider the logic statement:

4 X = ((A AND B) AND (A OR NOT C)) OR (B AND NOT C) (a) Draw a logic circuit to represent the given logic statement. [6] 1 mark per correct gate with correct inputs. (b) Complete the truth table for the given logic statement. A B C R S T U V X 0 0 0 0 1 1 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 1 1 0 1 1 0 1 1 0 0 0 0 0 0 1 0 0 0 1 1 0 0 0 1 0 1 0 1 0 0 0 0 1 1 0 1 1 1 1 1 1 1 1 1 1 1 0 1 0 1 [4] 5 Phishing and pharming are two examples of online security threats to a computer system. A B C X T S U V R

5 (a) Explain what is meant by phishing and pharming. (a) Four from: Phishing: - A legitimate looking email is sent to a user - The email will provide the user with a link/open an attachment - The link will redirect a user to a legitimate looking webpage (to steal personal data) Pharming: - Manipulating a user’s computer by installing malicious code on a user’s hard drive/server - The code will cause a redirection to a legitimate looking webpage (to steal personal data) [4] (b) Identify two other online security threats to a computer system. (b) Two from: - Hacking - Virus - Denial of service - Spyware - Worms - Trojan Horse [2] (c) Give two security measures that can help to protect a computer system from online security threats. (c) Two from: - Firewall - Proxy server - Anti-virus - Anti-malware - Anti-spyware - Username and password [2] 6 Darryl stores data electronically.

6 Describe two methods that he could use to avoid loss of stored data. Backups - Make a copy of the data - Copy stored away from main computer - Data can be restored from backup Anti-virus - Scans computer for viruses - Software to detect/remove viruses - Can prevent data being corrupted by viruses Firewall - Hardware or software that monitors network traffic - To help prevent hackers gaining access / deleting data Password/Biometrics - To help protect files/computer from unauthorised access Restricted access - To stop users downloading/installing software that could harm Verification - Message to ask user if user is sure that file is to be deleted Physical methods - Locks/alarms/CCTV to alert/deter unauthorised access [4]

7 7 The following checks the level of chlorine and the depth of water compared to the height of the swimming pool. Error messages are output if a problem is found. START END INPUT Height, Depth, Chlorine OUTPUT “Water too deep” OUTPUT “Water too shallow” OUTPUT “Too much chlorine add more water” OUTPUT “Too little chlorine add more chlorine” OUTPUT “Pool OK to use” Is Depth > Height/2? Is Depth < Height/3? Is Chlorine > 3? Is Chlorine < 1? Is OK == True? OK = True OK = False Yes Yes Yes Yes Yes No No No No No

8 (a) Complete the trace tables for each set of input data. Input data: 6, 2.5, 2 Height Depth Chlorine OK OUTPUT 6 2.5 2 True Pool OK to use Input data: 4, 3, 1.5 Height Depth Chlorine OK OUTPUT 4 3 1.5 True Water too deep False Input data: 6, 3.5, 4 Height Depth Chlorine OK OUTPUT 6 3.5 4 True Water too deep False Too much chlorine add more water [6] (b) Identify a problem with the algorithm that the flowchart represents. Any one from: - Cannot add more water if the water is too deep - No validation e.g. allows a negative height/depth/amount of chlorine - Tells you to add chlorine when there is no water Runs only once [1] 8 Describe two differences between Read Only Memory (ROM) and Random Access Memory (RAM). Difference 1 …………………………………………………………………………………….. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. Difference 2 …………………………………………………………………………………….. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. …………………………………………………………………………………………………….

9 Any 2 sets of points from: - ROM is permanent memory… - … RAM is temporary memory - ROM is non – volatile - … RAM is volatile … - ROM is read only … - … RAM can have read/write operations - ROM holds instructions for