SPS 2022 Sec 4E Computing Prelim P1 MS

Sec 4 O Level Prelim 2022 Computing Marking Scheme 1 Function Description COUNT • • Counts the number of cells that are not empty. COUNTA • • Counts the number of characters in a cell. COUNTIF • • Counts the number of cells within a range that meet a specified condition. • Counts the number of cells that contain numeric data. [3] 2(a) When the Central Processing Unit (CPU) receives an instruction to write data to the memory, the uni-directional address bus carries the destination address from CPU to memory. The data bus carries the data to be written. The speed of a CPU is usually measured in gigahertz. Temporary memory refers to Random Access Memory. This memory is volatile, which means all data and instructions stored on it are erased when the computer is switched off. [1] [1] [1] [1] [1]

2(b) (i) A bit is the smallest unit of data in a computer, which can take on the value of either 0 or 1. A byte is a unit of data made up of eight bits [1] [1] (ii) 139 MB = 139 000 KB 2 450 000 000 B = 2.45 GB [1] [1] 3 Problem Effect Method of keeping data safe Power failure If the power supply to a computer fails, data that is in the process of being written to a storage device may become corrupted and data that is stored in volatile memory but not yet written to a storage device will be lost. Set up a backup po wer supply or uninterruptible power supply (UPS) so storage devices can complete any write operations in case of a power failure. Human error EITHER ONE: • Storage devices may be accidentally damaged during transport. • Multiple users working on the same file may accidentally overwrite each other’s data. EITHER ONE: • Make regular backups of data. • Use adequate protection when transporting storage devices. • Set up rules when collaborating with multiple users to prevent them from writing to the same file at the same time. Computer Virus Virus may purposely damage and corrupt data as a way of attacking the computer. EITHER ONE: Avoid opening email/chat attachments or files from unknown sources. Install and configure a firewall to prevent them from spreading through the network. Install anti -virus and anti-spyware software, as well as perform regular scans and updates. Each correct box [1m]. Penalise for repeated effect / method. [6]

4 (a) Compilers and interpreters translate/convert source code (which humans can understand) into machine code (which only computers understand). 1 mark for general explanation 2 marks if source code and machine code are explained [2] 4(b) 1) In a compiler, source code is translated into machine code completely before the compiled program can be run. [1] In an interpreter, the source code to machine code translation happens while the interpreted program is running concurrently. [1] 2) In a compiler, syntax errors are detected (during the compilation phase) before the program is run. [1] In an interpreter, syntax errors may interrupt the running of a program. [1] Alternative answer: The compiler is not required to run the program after compilation is completed. [1] The interpreter needs to be run every time the program is used (because the program can only be run through the interpreter). [1] [4] 5(a) Input: time_spent: number of hours travelling to work every day Output: Average number of hours spent travelling to work Processes required: Sum up the total number of hours spent travelling for one month and divide by the number of days [1] [1] [1] 5(b) Input: equipment_list: equipment requiring electrical energy consumption_list: energy consumption of the list of equipment Output: Electrical equipment with highest energy consumption Processes required: Step 1: Compare the energy consumption of first equipment with the energy consumption of second equipment in the consumption_list. Pick the higher consumption Step 2: Repeat step 1 for subsequent items in the consumption_list until the end of the list has been reached. Step 3: Obtain the equipment from the equipment_list with the highest energy consumption. [1] [1] [1]

6 (a) 01 move = [“Rock”, “Scissors”, “Paper”] 02 quitGame = FALSE 03 WHILE quitGame == FALSE #loop until game ends 04 OUTPUT(“Enter 1 for Rock.”) 05 OUTPUT(“Enter 2 for Scissors.”) 06 OUTPUT(“Enter 3 for Paper.”) 07 OUTPUT(“Enter 0 to exit.”) 08 INPUT user 09 IF user != 0 10 IF user < 1 or user > 3: 11 OUTPUT (“ENTER a valid choice!”) 12 CONTINUE #skips the rest of the code below and repeats at line 03 13 ENDIF 14 computer = RANDINT(1,3) 15 OUTPUT(“You picked ”, move[user - 1]) 16 OUTPUT(“Computer played”, move[computer - 1]) 17 IF computer == user 18 OUTPUT(“It is a tie!”) 19 ELSEIF computer == 1 and user == 2 20 OUTPUT(“Computer wins!”) 21 ELSEIF computer == 2 and user == 3 22 OUTPUT(“Computer wins!”) 23 ELSEIF computer == 3 and user == 1 24 OUTPUT(“Computer wins!”) 25 ELSE 26 OUTPUT(“You win!”) 27 ENDIF 28 ELSE 29 quitGame = True 30 OUTPUT(“Thank you for playing, goodbye!”) 31 ENDWHILE Error 1: Line 02: quitGame = TRUE Correction: quitGame = FALSE Error 2 Line 10: IF user < 1 or user < 3 Correction: IF user < 1 or user > 3 Error 3 Line 17: IF computer != user Correction IF computer == user Error 4 Line 21: ELSEIF computer == 2 and user == 0: Correction ELSEIF computer == 2 and user == 3 [4]

(b) Error type 1: Syntax error [1m] Description: Result of incorrect source code that does not follow the rules of the language [1m] Error type 2 Runtime error [1m] Description: Error that occurs while the program is running (e.g. input data that has not been properly validated by a format check to ensure that it is a valid integer) [1m] [4] (c) Test case condition Test data Normal 2 3 Error 3.0 “ ” or “two” Note: reject out of range test date (e.g. 0, 4, etc), those belong to Boundary. [4] 7 (a) X P Q R S G H OUTPUT 0 1 2 3 0 0 1 2 1 9 3 4 2 1 13 4 3 28 1 4 33 14 6 5 2 34 24 6 46 0 7 44 [1]

7(b) H counts the number of X inputs divisible by 3. [1] 8 1 mark for every 2 correct logic gate. [4] 9 To convert a binary number to its hexadecimal equivalent, we split the number into groups of four binary digits, starting from the right. If a group does not have the full set of four binary digits, add leading zeros to that group until it is a full set of four binary digits. Then convert each four-digit binary group into its corresponding hexadecimal digit using a conversion table. Hexadecimal value: BD16 [1] [1] [1] 10(a) A series of computing devices connected together. [1] (b) A hub broadcasts the data packet to all computers in the network. A switch only broadcasts it to the computer that is meant to receive it. [1] [1] (c) All the devices are connected to the central server. Data that needs to be shared are hosted on the central server and access can be controlled through the server. Additional devices can be easily added by connecting them to the central server. [Accept other reasonable answers] [1] [1] [1] (d) (i) 1 0 0 1 0 1 1 0 A B C Q

Correct parity bit value 1 [1m] Correct prepended parity bit position at the beginning of data [1m] [2] (ii) Any 1 from the following. Maximum 1 mark. • Even number of incorrect bits (or 2 errors / even errors) can cance