2022 MSHS S4 Prelims Paper 1 Answers final

Class/ Index Number / Centre Number/ ‘O’ Level Index Number / Name MARIS STELLA HIGH SCHOOL PRELIMINARY EXAMINATION SECONDARY FOUR COMPUTING 7155/01 Paper 1 Written 23 August 2022 2 hours Candidates answer on the Question Paper. No Additional Materials are required. MARKING SCHEME For Examiner’s Use This document consists of 16 printed pages. 80

2 1 Five data loss issues are shown on the left. Six possible methods of data recovery or protection are shown on the right. Draw one line to link each issue to its correct method . Data Loss Issues Methods Data loss caused by hard disk head crash Anti-virus software Hacking into files and changing or deleting data Encryption A computer program that attaches itself to a harmless program and modifies it Read policy privacy An intruder with physical access to a storage device accessing files or folders Anti-spyware software Software that logs/records all key presses on your computer without you knowing Create back-up files Use of passwords and firewall [5]

3 2 There are five stages in developing a program. Identify three stages and elaborate the process of each stage. 1 mark to identify the stage, 1 mark for explaining what happens at that stage 1 – Gather Requirements • Determine the nature of the problem by interviewing the intended audience of the program • Identifying a set of input necessary and how input will be collected • Identifying what outputs are required and how output will be given 2 – Plan Solutions • Manually solving different simplified examples of the problem and generalising the steps needed to produce the required output (apply generalising to solve problem and plan solution) • Trying different ways to break down the problem into smaller parts such that the intended output of each part gets closer and closer to what is needed to solve the problem(apply decomposition to solve problem and plan solution) • Comparing the problem to other problems that have been solved before and identifying which algorithms can be used. • Estimating the amount of effort needed to write the code or the time needed to complete the algorithm before making a definite choice ( plan logistics and project timeline) • Writing possible algorithms using either flowcharts or pseudo-code 3 – Write code • Write code that performs the algorithm as planned in the previous stage as efficiently as possible. 4 – Test and Refine Code • Running the code through one or more test cases to evaluate whether the written code adequately satisfies the gathered requirements and is ready to be used. 5 – Deploy Code • To allow program to be used by intended audience by training users to use the program. • Transitioning from an old program or system to the new program. • Evaluating the effectiveness of the program in solving the problem and considering any changes that might increase its usability or effectiveness. [6]

4 3 (a) Read the following section of a program code that inputs twenty numbers and then outputs the largest number input. 1 highest = 0 2 count = 0 3 while count < 20: 4 number = int ( input ( “Please enter a number: “ ) ) 5 if number < highest: 6 number = highest 7 count = count + 1 8 print ( “The highest number is “, highest ) There are three errors in this code. Locate these errors and suggest a corrected piece of code. 1 mark for each correct correction Line 5 if number > highest: Line 6 highest = number Line 8 print ( “The highest number is “, highest ) (student needs to explain or show the need to remove indentation or to bring the print statement outside the loop) or Remove indentation so the print statement is outside of the loop [3] (b) (i) Identify the type of errors found in part (a) Logic error [1] (ii) Identify and describe another type of error not found in part (a) 1 mark for the type of error and 1 mark for the description Syntax Errors – Errors that are due to incorrect source code that does not follow the rules of the language. Run-time Errors – Errors that are detected while a program is running, usually causing the program to crash or hang. [2]

5 (c) The program code is to be interpreted rather than compiled. Give one difference between these two methods. Any one of the following: - Compiled code will not need the compiler program to run, but code to be interpreted will require the conversion program to run. - Interpreter converts each line one at a time, while compiler converts the whole program into an executable file - Interpreter locates errors as it runs while the compiler detects syntax errors before the program is even run. [1] 4 The table contains statements about types of memory and secondary storage. Tick (  ) one or more boxes in each row to indicate if the statement is about RAM, ROM or Secondary Storage. Statement Secondary Storage RAM ROM Data is retained when electrical supply is cut off   Stores data that is currently being used by the processor  Data is lost when the power is switched off  Data can be stored in this device while the computer is running   [4]

6 5 (a) Complete the truth table for the following logic circuit: A B C P Q R S X 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 1 0 1 0 1 1 0 0 1 0 1 1 0 0 0 1 0 0 0 1 0 1 0 0 0 0 0 1 1 0 1 0 1 0 1 1 1 1 1 0 1 0 1 (b) What could replace the whole logic circuit? Replace the logic circuit with input B only [1] A B C X P Q R S 1m 1m 1m 1m

7 (c) Draw the logic circuit for the following logic statement: X = 1 if (A is NOT 1 AND B is 1) AND ( B is NOT 1 OR C is 1 ) [5] 6 A program has been written to process students’ marks in a set of tests. (a) Describe two validation checks that could be made on a student’s name. 1 mark each length check – to ensure up to 30 letters of alphabet only (number of letters can be any value reasonable for a long name) character/format check – to ensure name doesn’t contain numeric characters (b) Describe two validation checks that could be made on the test marks. 1 mark each range check – to ensure marks are within correct boundaries (e.g. between 0 and 100) length check – to ensure no more than 3 digits are input [4] A B C X

8 7 An encryption system assigns a value to each letter of the alphabet: A = 1, B = 2, C = 3, ……… , Y = 25, Z = 26 Each letter is stored in a 12-bit binary register. The letters “S” (19th letter) is stored as: 2048 1024 512 256 128 64 32 16 8 4 2 1 0 0 0 0 0 0 0 1 0 0 1 1 A 4-bit register is used to store the encryption key. This register shows how many places the bits are shifted to the left in the 12-bit register when it is encrypted. For example, 8 4 2 1 0 1 0 1 means each bit in the 12-bit register is shifted 5 places to the left and the register now becomes: 2048 1024 512 256 128 64 32 16 8 4 2 1 0 0 1 0 0 1 1 0 0 0 0 0 Therefore, the letter “S” would be transmitted with the 4-bit register and the 12-bit register as a 16-bit register as follows: Encryption Key Data bits 0 1 0 1 0 0 1 0 0 1 1 0 0 0 0 0 (a) “W” is the 23rd letter of the alphabet. (i) How is the letter “W” represented in the 12-bit register, before encryption?