2022 MSHS S4 Prelims Paper 1 Qns 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. READ THESE INSTRUCTIONS FIRST Write your class, index number, Centre number, O level index number and name in the spaces at the top of this page. Write in dark blue or black pen. You may use a HB pencil for any diagrams or graphs. Do not use staples, paper clips, highlighters, glue or correction fluid. Approved calculators are allowed. Answer all the 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. For Examiner’s Use This document consists of 14 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 Issue Method 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] 2 There are five stages in developing a program. Identify three stages and elaborate the process of each stage. 1 ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… 2 ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… 3 ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… [6]

3 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. Error 1 Line …………………….…………………….……………………………………………. Error 1 Correction …………………………………………………………………………………. Error 2 Line …………………….…………………….……………………………………………. Error 2 Correction …………………………………………………………………………………. Error 3 Line …………………….…………………….……………………………………………. Error 3 Correction …………………………………………………………………………………. [3] (b) (i) Identify the type of errors found in part (a) ………………………………………………………………………………………………… [1] (ii) Identify and describe another type of error not found in part (a) Type of Error …...…………………………………………………………………………… Describe ...…………………………………………………………………………………… ………………………………………………………………………………………………… [2] (c) The program code is to be interpreted rather than compiled. Give one difference between these two methods. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. [1]

4 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] 5 (a) Complete the truth table for the following logic circuit: A B C Working Space X 0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1 [4] (b) What could replace the whole logic circuit? ………………………………………………………………………………………………………. [1] A B C X

5 (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 .……………………………………………………………………………………………………. ………………………………………………………………………………………………………. 2 .……………………………………………………………………………………………………. ………………………………………………………………………………………………………. (b) Describe two validation checks that could be made on the test marks. 1 .……………………………………………………………………………………………………. ………………………………………………………………………………………………………. 2 .……………………………………………………………………………………………………. ………………………………………………………………………………………………………. [4] A B C X

6 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? 2048 1024 512 256 128 64 32 16 8 4 2 1 [1] (ii) The 4-bit register contains the following value: 8 4 2 1 0 1 1 0 How is the letter “W” stored in the 12-bit register, after encryption? 2048 1024 512 256 128 64 32 16 8 4 2 1 [1]

7 (b) A 4-bit register and a 12-bit register is shown below. Which letter of the alphabet has been transmitted? (Explain how you got your answer.) Encryption Key Data bits 0 0 1 1 0 0 0 0 1 1 0 0 1 0 0 0 ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. ………………………………………………………………………………………………………. [2] (c) (i) What is the largest encryption key that can be stored in the 4-bit register? 8 4 2 1 [1] (ii) Convert this into denary (base 10). ………………………………………………………………………………………………… [1] (iii) If this encryption key were used, what problem would it cause? ………………………………………………………………………………………………… ……………………………………………