JYSS 2018 P1 Solution

Answers 1 (a) RING Network - Any TWO from: [textbook] Advantages Disadvantages • Can operate over larger distances and handle more data • If a computer or cable in the network fails, the entire network may fail as the data cannot be passed on • Data packets that are sent between two computers will pass through intermediate computers, hence a central server is not required to manage the network • Adding a new computer to the ring network would mean that the whole communication ring needs to be temporarily interrupted -shared resources -less efficient than star because it needs to travel through all other work stations first to get to destination work station -a faulty connection between two stations can cause network failure -it is difficult to add a new station/device as it has to come between 2 existing stations -this type works well during heavy loading -it is possible to create large networks using this topology (b) STAR Network - Any TWO from: [textbook] Advantages Disadvantages • The load on each section of cabling is reduced as each computer uses a separate cable from the rest • Uses more cabling than other topologies and hence costs more • If a fault occurs at a computer or cable, it is easy to isolate the fault and do a replacement without affecting the rest of the network • If the central network device fails, the entire network fails -shared resources -cable failure isolates/affects only the work station where cable failed -if one station/connection fails the other devices are not affected -if the central hub breaks down, the whole network fails -it is easier to identify faults using this type of topology -it is easy to expand this type of network

2 2 1 mark for each correct tick 3 Description It is more difficult to debug the code since one error can produce many other associated errors. The speed of execution of program loops is slower. Compiler It produces fast, executable code that runs directly on the processor. Interpreter It is easier to debug the code since an error is displayed as soon as it is found. Statement True (/) False (/) Firewalls can monitor incoming and outgoing traffic. ü Firewalls cannot block access to a certain website. ü Firewalls can be software and hardware. ü Firewalls can act as intermediary servers. ü Firewalls can block unauthorised traffic. ü

3 4E Computing P1 2018 Prelim [Turn over 4 (a) (i) – value of count starts at 1 so only 999 iterations – value of count reaches 1000, but before 1000th input (ii) – line 1 should read count = 0 – line 5 should read count = 1001 (or count >1000) – change to appropriate loop structure [2] (b) (i) – normal/valid (test data) – any value in given range (1 to 12) e.g. 4 (ii) – abnormal/invalid (test data) – any value which is outside the range/any value not acceptable – i.e. letters, negative numbers, values > 12 e.g. adfrk, -20, 36 (iii) – extreme/boundary (test data) – data which is on the boundaries/edges of the acceptable range – i.e. 1 or 12 for extreme; 0, 1, 12 or 13 for boundary – Month names, instead of values, are acceptable e.g. April 5 Line 4 correct line WHILE Number <= 99 OR Number > 1000 Line 7 correct line Num[Index] = Number Line 9 correct line NEXT (Index) Line 10 correct line PRINT Count 6 (a) (i) Plagiarism (ii) Free and Open-Source software (iii) Freeware (iv) Shareware (v) Ethics (b) File name: ComputingPapers Protocol: http(://) Web server name: www.junyuansec.moe.edu.sg (c) (i) First six digits: manufacturer code/manufacturer ID (ii) Last six digits: serial number/serial ID of device/product

4 7 viruses: – malicious code which self replicates – designed to delete, alter or corrupt files phishing: – sending emails to recipients claiming to be a legitimate company – when email opened, recipient is directed to a bogus website/gets details about customer pharming: – malicious code installed on PC or a server – code misdirects user to a fraudulent website (without their knowledge) hacking: – unauthorised access to a computer system – in an effort to use data illegally (e.g. fraud) – to change/delete/corrupt data on a computer key logging/spyware – program installed on a computer to monitor all key presses – each key press is relayed back to the program writer or spyware – scan files on hard drive – ‘snoop’ applications shoulder surfing: – the act of watching a person key in secure data (e.g. PIN, password, etc.) – stealing security data by using binoculars, CCTV near ATMs etc. to watch key presses etc 8 (a) A B X C D E F

5 4E Computing P1 2018 Prelim [Turn over (b) Input Working space Output A B C D E F X 0 0 0 1 1 0 1 0 0 1 1 0 0 1 0 1 0 0 1 1 1 0 1 1 0 0 0 0 1 0 0 0 1 0 0 1 0 1 0 0 0 0 1 1 0 0 1 1 1 1 1 1 0 0 0 0 (c) X = (NOT A NAND B) AND (B OR C) 9 HighF HighC TempF OUTPUT –100 –100 68 68 18 46 68 18 50 68 18 86 86 27 65 86 27 50 86 27 40 86 27 30 86 27 –1 The highest temperature is, 86 Fahrenheit, 27 Celsius 10 (a) (i) (byte) 5 (ii) (column) 4 (iii) corrected byte is: 1 0 0 1 1 1 1 1 (iv) that gives the value: 1 5 9

6 (follow through applies) (b) Two marks for each correct description (i) Check digit • A digit that is calculated from the data // uses modulo to calculate digit // valid description of modulo • It is appended / added to the data • Digit is recalculated when data is entered • Digits are compared to check for error (ii) Checksum • A value is calculated from the data // Valid description of calculation • It is transmitted with the data • Value is recalculated after transmission • Values are compared after transmission to check for error 11 (a) (i) 2 marks for 3 correct binary conversions, 1 mark for 2 correct binary conversions (ii) 1 mark for each correct hex value converted 1 A F (b) 1 mark for working + 1 mark for correct answer Working – 1200 × 8 = 9600 (bytes) – 9600/1024 or 9600/1000 Answer – 9.4 or 9.6 kilobytes 0 0 0 1 1 0 1 0 1 1 1 1

7 4E Computing P1 2018 Prelim [Turn over (c) Any one from: MAC (Media Access Control) address – unique number that identifies a device (connected to the Internet) – address is made up of manufacturer id + serial number of device – address is allocated by the manufacturer Any one from: IP (Internet Protocol) address – location/address of a device on the Internet – address is unique for given Internet session – address is supplied when a device connects to the Internet – address is allocated by the network 12 Sample program in pseudocode: largest = 0 smarket1 = 0: smarket2 = 0 for item = 1 to 1000 input price1, price2 if price1 > price2 then smarket1 = smarket1 + 1 if price2 > price1 then smarket2 = smarket2 + 1 difference = price1 – price2 if difference < 0 then difference = - difference if difference > largest then largest = difference next item output smarket1, smarket2, largest