2021 BLSS Computing P1 Solutions

BLS/PRELIM/2021/4E/COMP/7155/01 BOON LAY SECONDARY SCHOOL PRELIMINARY EXAMINATION 2021 Name CCA Subject : COMPUTING Paper No : 1 Subject Code : 7155/01 Level : SECONDARY FOUR EXPRESS Date/Day : 30th AUGUST 2021 / MONDAY Time : 1100 – 1300 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 12 printed pages.

2 BLS/PRELIM/2021/4E/COMP/7155/01 1 Digital systems make use of several different methods to store data. a (i) Explain what is meant by “hexadecimal digits”. Base 16, numbers are from 0 to 9, A to F. …………………………….…………………………………………………………………...[1] (ii) Describe two examples where a hexadecimal storage system would be preferred over a denary system. file compression, MAC addresses, colour codes, encryption [Any two] …………………………….…………………………………………………………………...[2] (iii) Justify the use of hexadecimal storage systems in one of your examples in a(ii). Able to represent more data with the same number of bits. [1] 4-bit binary word: max – 1111 = 15. 4-bit hexadecimal word: FFFF = 65535 [1] b (i) The character Omega, “Ω” is represented by the binary number 11101010 in ASCII. Convert 11101010 into a denary number. Show your working. 7 6 5 4 3 2 1 0 128 64 32 16 8 4 2 1 1 1 1 0 1 0 1 0 128 64 32 0 8 0 2 0 128 + 64 + 32 + 8 + 2 = 234 …………………………….…………………………………………………………………...[1]

3 BLS/PRELIM/2021/4E/COMP/7155/01 (ii) The character “j” is represented by the denary number 106 in ASCII. Describe a method to convert 106 into its hexadecimal representation. 1 – convert 106 to binary = 01101010 2 – break into words of 4-bits = [0010] [1010] 3 – convert the binary words into their hexadecimal equivalents = 6A …………………………….……………………………………………………………………… …………………………….……………………………………………………………………… …………………………….……………………………………………………………………… …………………………….……………………………………………………………………… …………………………….…………………………………………………………………...[3] 2 a Where appropriate, draw a line to match the terms to its correct description. Terms Description DoS attack ¢ Cookie ¢ ¢ A small piece of data used by websites to store personal information on a user’s web browser. Encryption ¢ ¢ Hidden program that secretly collects personal information.