BLSS Paper 1[Ans][Vetted]

BOON LAY SECONDARY SCHOOL PRELIMINARY EXAMINATION 2022 Name CCA Subject : COMPUTING Paper No : 1 Subject Code : 7155/01 Level : SECONDARY FOUR EXPRESS Date/Day : XX XXX 20XX / XXXXESDAY Time : XXXX – XXXX Duration : 2 HOURS Candidates answer on the Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Before you start your exam, check that you have received the correct paper and the number of printed pages are correct. Write your name, index number, and CCA in the spaces at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs or rough working. Do not use staples, paper clips, glue or correction fluid. Approved calculators are allowed. Answer all 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. This document consists of 13 printed pages.

2 BLS/PRELIM/2022/4E/COMP/7155/01 1 (a) A computer is a complex electronic device that utilizes many different components to perform calculations and output the desired results. (i) Buses are used to transfer data from one part of a computer to another. Draw one or more lines to match the type of bus (left) to their correct description(s) (right). Type of bus Description Transports information from memory to processor when reading data from memory Data bus Transports information from memory to processor when writing data to memory Transports information from processor to memory when reading data from memory Address bus Transports information from processor to memory when writing data to memory [2] (ii) What are the two components inside a CPU and what are their respective functions? Component 1 : Control Unit Function: Coordinates all input, output and data transfer functions in the computer …………………………………………………………………………………………………… ………………………………………………………………………………………………...[2] Component 2 : Arithmetic Logic Unit Function: Performs all logical and mathematical calculations …………………………………………………………………………………………………… ………………………………………………………………………………………………...[2]

3 BLS/PRELIM/2022/4E/COMP/7155/01 (b) RAM is placed near to the CPU as it is a “volatile” memory. (i) Explain the term “volatile” in this context. It means that data will be erased once the memory loses power. …………………………………………………………………………………………………… ………………………………………………………………………………………………...[1] (ii) State two functions of RAM. It stores data and programs that are frequently used. It stores temporary data or results from intermediate calculations. …………………………………………………………………………………………………… ………………………………………………………………………………………………...[2] (iii) Other than being volatile, state another characteristic of RAM and explain why it is placed near the CPU. It is very fast – able to read and write very quickly. It is placed near the CPU to reduce the time needed to transfer data between the CPU and the RAM. ………………………………………………………………………………………………...[2] (c) Data for longer-termed storage is usually kept in secondary storage drives. (i) Provide an example of data that is usually kept in secondary storage drives and explain your choice. An archive of photos / Any other reasonable answer. As an archive, the photos do not need to be accessed frequently and can thus be stored on secondary storages which are slower but also cheaper. ………………………………………………………………………………………………...[2]

4 BLS/PRELIM/2022/4E/COMP/7155/01 (ii) Explain how data in secondary storage devices can be accidentally damaged without internet access. There could be malfunctions in the reading and writing sequences that caused data corruption. OR, there could have been an interruption during the transmission of data resulting in the loss of data. ………………………………………………………………………………………………...[2] 2 (a) A simple home network can allow for devices in a home to connect to the internet. (i) State the function of the following networking hardware. Network interface controller Allows a computer or hardware to connect to a network. …………………………………………………………………………………………………… ………………………………………………………………………………………………...[1] Network hub Receives an input packet and broadcasts it to all the devices connected to it. …………………………………………………………………………………………………… ………………………………………………………………………………………………...[1]

5 BLS/PRELIM/2022/4E/COMP/7155/01 (ii) In the space provided below, construct a simple home network that would allow devices to connect to the internet. Your network must consist of the following: • Modem • Router • Network Switch You should use well labelled boxes to represent the hardware. [3] (b) (i) State and explain if a home network should use a wired or wireless setup. (Accept either answer with reasonable justifications) Wired – higher speed, more secure, reliable Wireless – decent speed, higher mobility, easy to add devices. …………………………………………………………………………………………………… …………………………………………………………………………………………………… ………………………………………………………………………………………………...[3] Home Desktop Internet Modem Router Home Laptop Network Switch

6 BLS/PRELIM/2022/4E/COMP/7155/01 (ii) The table below shows three common network topologies. Label them with their correct names and state a feature of each topology. Name Bus Ring Star Feature Unidirectional Messages travel through all computers in the network Easy to add / remove nodes [6] (c) (i) Explain the need for parity bits and checksums in data transmissions. During transmission, there can be packet (data) losses due to transmission errors that might occur over long distances. Parity bits and checksums provide a simple low-level method to determine if packets received are correct. ………………………………………………………………………………………………...[2] (ii) Explain how checksums can be used in a network. A checksum is calculated using a predetermined hashing function (calculation steps) and is applied on every packet of data. This checksum is also transmitted to the receiver. When the receiver receives the data packet and the checksum, it will generate its own checksum value from the data packet to determine its integrity. …………………………………………………………………………………………………… ………………………………………………………………………………………………...[3]

7 BLS/PRELIM/2022/4E/COMP/7155/01 3 (a) The development of a program involves many stages. (i) Draw lines to connect the descriptions on the left to the correct stages of developing a program on the right. Description Stage Gather requirements Train users to use the program. Plan solutions Compare the actual output with expected output. Write code Determine the complete set of outputs that is necessary to solve the problem. Test and refine code Write possible algorithms using either flowcharts or pseudo-code. Implement code [2] (ii) Explain why it is necessary to plan, test and refine the code before implementing it. It is to ensure that the exact requirements of the program are known so that time spent writing code will be meaningful. This also allows the programmer to cater to the necessary error, boundary and normal test cases that are required. ………………………………………………………………………………………………...[2]

8 BLS/PRELIM/2022/4E/COMP/7155/01 (b) The code below was found in an unnamed python file without any instructions. Study the code carefully and answer the questions that follow. list1 = ["M", "na", "i", "Ke"] list2 = ["y", "me", "s", "lly"] list3 = [] for i in range(len(list1)): list3.append(list1[i]+list2[