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 progr