BLSS 2019 P1

BOON LAY SECONDARY SCHOOL PRELIMNARY EXAMINATION 2019 Name [ ] CCA Subject : COMPUTING Paper No : 1 Subject Code : 7155/01 Level : SECONDARY FOUR EXPRESS Date/Day : 17 SEPTEMBER 2019 / TUESDAY Time : 1030 - 1230 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.

2 BLS/EYE/2019/4E/COMP/7155/01 This document consists of 13 printed pages. 1 (a) Denary numbers are stored as binary numbers inside a computer. (i) Convert the denary number 168 into 8-bit binary. Show your working. ……………………………………………………………………………………………………. ………………………………………………………………………………………………….[1] (ii) Convert the positive whole binary number 11010011 into a denary number. Show your working. ……………………………………………………………………………………………………. ………………………………………………………………………………………………….[1] (iii) Convert the hexadecimal number AC into its binary representation. Show your working. ……………………………………………………………………………………………………. ………………………………………………………………………………………………….[1] (b) Hexadecimal numbers are commonly used in file compression techniques and in Media Access Control (MAC) addresses. (i) Identify and calculate the largest denary value that can be stored by the following numbers. Show your working. A 4-character binary number ……………………………………………………………………………………………………. ………………………………………………………………………………………………….[1] A 4-character hexadecimal number ……………………………………………………………………………………………………. ………………………………………………………………………………………………….[1]

3 BLS/EYE/2019/4E/COMP/7155/01 (ii) State and describe one other use of the hexadecimal number system. ……………………………………………………………………………………………………. ………………………………………………………………………………………………….[2] 2 A computer network is a system of two or more computers that are connected together by a transmission medium for the exchange of data. (a) The diagram below shows how a home network is connected to the Metropolitan Area Network (MAN). (i) Complete the diagram by filling in the appropriate networking devices for the three parts labelled i., ii., and iii. Networking devices: Router, Modem, Bridge, Network Interface Card i. ………………………………………………………………………………………………… ii. ………………………………………………………………………………………………… iii. ………………………………………………………………………………………………[2] (ii) Explain the functions of the following networking devices: Router ……………………………………………………………………………………………………. MAN i. Home network ii. iii. Server Home terminal Mobile devices iii.

4 BLS/EYE/2019/4E/COMP/7155/01 ……………………………………………………………………………………………………. …………………………………………………………………………………………………[2] Network Interface Card (NIC) ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. …………………………………………………………………………………………………[2] (b) (i) Compare the difference in purpose and functionality between a client-server network and a peer-to-peer network. You may use an example to aid your answer. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ………………………………………………………………………………………………….[3] (ii) With reference to the transfer of information to terminals on a network, explain one difference between a bus and a star network. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ………………………………………………………………………………………………….[2] (iii) Explain what are parity bits and benefits of using parity bits in data communication. Include the working principle of either odd or even parity bits. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. …………………………………………………………………………………………………….

5 BLS/EYE/2019/4E/COMP/7155/01 ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ………………………………………………………………………………………………….[4] 3 Consider the following algorithm. 1 x = 0 2 y = 0 3 while True: 4 num = input("Key in an integer: ") 5 out = 0 6 for i in range (len(num)): 7 out += int(num[i])*i 8 if out % 5 == 0: 9 x += 1 10 else: 11 y += 1 12 print("X: {}, Y: {}".format(x,y)) 13 if (input("Try another number? (Y/N)").upper() != 'Y'): 14 break (a) (i) Complete the trace table for the algorithm. Use the data 1522, Y, 66733, Y, 23452, y, 35323, y, 1234, n, 8572, Y x y out [5] (ii) State the purpose of the algorithm. Assume only valid inputs are keyed in. ……………………………………………………………………………………………………. …………………………………………………………………………………………………….

6 BLS/EYE/2019/4E/COMP/7155/01 ………………………………………………………………………………………………….[2] (b) (i) Explain a benefit of including input validation checks in a computer program. ……………………………………………………………………………………………………. …………………………………………………………………………………………………[1] (ii) Write a validation check for the user input in the program above using pseudo code. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. …………………………………………………………………………………………………[3] 4 State the function and describe one difference for each of the following (a) (i) Data and address buses Function: …..……………………………………………………………………………………. ……………………………………………………………………………………………………. Difference: ………………………………………………………………………………………. ………………………………………………………………………………………………….[3] (ii) Memory and external storage Function: …..……………………………………………………………………………………. ……………………………………………………………………………………………………. Difference: ………………………………………………………………………………………. ………………………………………………………………………………………………….[3] (b) Complete the truth tables for the gates shown below: NAND gate Input 1 Input 2 Output 0 0 NOR gate Input 1 Input 2 Output 0 0

7 BLS/EYE/2019/4E/COMP/7155/01 0 1 1 0 1 1 0 1 1 0 1 1 [2] 5 (a) Draw the logic circuit to represent the following Boolean statement. Do not simplify the statement. X = (A OR B) AND (NOT (A) OR C) [4] (b) Complete the truth table for the Boolean statement: X = (A OR B) AND (NOT (A) OR C) A B C Working Space X 0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 A- B- C- X-

8 BLS/EYE/2019/4E/COMP/7155/01 1 0 1 1 1 0 1 1 1 [3] 6 A receptionist at a hotel wrote a program to find out how many of his guests have first or last names that have at least 5 characters. The program also outputs the first and last names that have at least 5 characters. You may assume that all the names in the list namelst are valid and are made up of only two words. The first word in each name is the first name and the second word is the last name. 1 namelst=['Eryn Hobby', 'Sharie Walko', 'Corrine Rieck', 'Latina Carns', 'Jeanetta Mertens', 'Jenae Yoshimoto', 'Geoffrey Gause', 'Elaina Pack', 'Jenelle Brickhouse', 'Nathanial Jacoby', 'Ulrike Selleck', 'Maryellen Hurlbut', 'Mose Jenner', 'Randall Wozniak', 'China Erick', 'Annamaria Seeley', 'Reva Ryman', 'Tera Ling', 'Phil Kellison', 'Judith Larue', 'Elfreda Kallenbach', 'Cristina Hu', 'Serafina Theis', 'Tiesha Gero', 'Maryrose Mcdermott', 'Sheena Dawes', 'Shea Cag