IGCSE Computer Science 0478: questions by topic

1 A hockey club records the number of people that watch each match. An 8-bit binary register is used to store this value. (a) 46 people watch the first match and 171 people watch the second match. Show how the registers would store these denary values as 8-bit binary. Denary value 8-bit binary 46 171 [2] Working space (b) Give the largest denary value that can be stored in the 8-bit binary register. [1] (c) The hockey club wants to increase the number of people that can watch each match to 2000. The 8-bit binary register may no longer be able to store the value. Give the smallest number of bits that can be used to store the denary value 2000. [1] Working space (d) Electronic data about the final score for the match is transmitted to a central computer 30 kilometres away, using serial transmission. (i) Explain why serial transmission is more appropriate than parallel transmission in this scenario. [3] (ii) The data transmission is also half-duplex. Describe half-duplex data transmission. [2] (iii) The data transmission uses checksums. Describe how checksums are used to detect errors in data transmission. [3]

1 Benedict has a computer that is assigned an Internet Protocol (IP) address. The IP address is: 198.167.214.0 The IP address is represented as denary values. (a) Convert the denary values 167 and 214 from the IP address to 8-bit binary. 167 214 Working space [2] (b) Benedict’s computer is also assigned a Media Access Control (MAC) address. (i) Identify one similarity between an IP address and a MAC address. [1] (ii) Identify two differences between an IP address and a MAC address. Difference 1 Difference 2 [2]

1 A denary value can be converted into hexadecimal and binary. (a) Complete the table to show the hexadecimal and 8-bit binary values of the given denary values. Denary Hexadecimal 8-bit binary 49 123 200 [6] Working space (b) Give two benefits, to users, of converting binary values to hexadecimal. Benefit 1 Benefit 2 [2] (c) Hexadecimal is used to represent Hypertext Markup Language (HTML) colour codes in computer science. Identify three other ways that hexadecimal is used in computer science. 1 2 3 [3]

1 Greta has a computer that she uses for schoolwork and leisure. (a) The computer has the Media Access Control (MAC) address: 00:A0:C9:14:C8:29 (i) Tick (3) to show whether the MAC address is initially assigned to the computer by the network, the manufacturer or the user. Tick (3) Network Manufacturer User [1] (ii) The values in the MAC address are hexadecimal values. Convert the three given hexadecimal values into 8-bit binary. 14 A0 C9 [3] Working space (iii) Convert the two given hexadecimal values into denary. 29 C8 [2] Working space (b) Greta stores data on several off-line storage devices, including an external hard disk drive (HDD), a USB flash memory drive and a compact disc (CD). (i) Identify the type of storage for each device. External HDD USB flash memory drive CD [3] (ii) Describe the operation of a HDD and how it stores data. [4]

1 Binary is a number system that is used by computers. (a) Tick (3) one box to show whether binary is a base-2, base-10 or base-16 number system. Tick (3) Base-2 Base-10 Base-16 [1] (b) Hexadecimal and denary are number systems that can be used by programmers. Convert these four hexadecimal values into denary values. 09 10 28 A1 [4] Working space

1 (a) Denary is a number system that is used by programmers. Tick (✓) one box to show whether denary is a base-2, base-10 or base-16 number system. Tick (✓) Base-2 Base-10 Base-16 [1] (b) Hexadecimal values can be used to represent denary values. Convert these four hexadecimal values into denary values. 05 20 1A AB [4] Working space (c) Hexadecimal values can also be converted to binary values. Tick (✓) one box to show the correct 8-bit binary value for each hexadecimal value. (i) Hexadecimal value 25 Tick (✓) 00011001 00100101 10100001 [1] (ii) Hexadecimal value 1B Tick (✓) 00011011 10110001 00011010 [1] (d) (i) Give one way that hexadecimal is used in website development. [1] (ii) Give one way that hexadecimal is used in low-level programming. [1]

1 (a) Xia has three files stored on her computer. Tick (3) one box to show which is the largest file size. File size Tick (✔) 999 kB 1 MB 850 000 bytes [1] (b) Denise has three files stored on her computer. Tick (3) one box to show which is the smallest file size. File size Tick (✔) 4000 MB 2 GB 2 500 000 kB [1]

2 Gurdeep takes high definition photographs using a digital camera. She has set up a website where users can view thumbnails of her photographs. A thumbnail is a small version of the high definition photograph. (a) Gurdeep compresses the high definition photographs to create the thumbnails. She uses lossy compression. Describe how lossy compression creates the thumbnails. [3] (b) Gurdeep sets up a web server to host her website. She reads about an Internet Protocol (IP) address, a Media Access Control (MAC) address and a Uniform Resource Locator (URL). Draw a line to connect each term to the correct example. Term Example IP address 192.168.0.255 MAC address https://www.cambridgeinternational.org URL 00:15:E9:2B:99:3C [2] (c) Users can buy the high definition photographs from the website. When a user buys a high definition photograph, a Secure Socket Layer (SSL) connection is created. (i) Give one benefit of using an SSL connection. [1] (ii) Explain how the SSL connection is created. [4]

2 Julia inputs personal data into her computer. She stores three copies of the data using a hard disk drive (HDD), a solid state drive (SSD) and a USB flash memory drive. (a) Identify three devices Julia can use to input personal data into her computer. Device 1 Device 2 Device 3 [3] (b) Six statements are shown about HDDs, SSDs and USB flash memory drives. Tick (✓) to show which statements apply to each type of storage. Some statements can apply to more than one type of storage. USB flash memory Statement HDD SSD drive (✓) (✓) (✓) it has no moving parts it is non-volatile it can use NAND gates to store data it uses magnetic properties to store data it has the smallest physical size it has the slowest read/write speeds [6] (c) Julia uses a USB connection to transfer data onto her USB flash memory drive. (i) One benefit of using a USB connection is that it is a universal connection. State two other benefits of using a USB connection. Benefit 1 Benefit 2 [2] (ii) Identify the type of data transmission used in a USB connection. [1]

2 Data storage can be magnetic, solid state or optical. (a) Six statements are given about data storage. Tick (3) to show if the statement applies to magnetic, solid state or optical storage. Some statements may apply to more than one type of storage. Statement Magnetic Solid state Optical (3) (3) (3) no moving parts are used to store data pits and lands are used to store data data is stored on platters flash memory is used to store data parts are rotated to store data data can be stored permanently [6] (b) (i) Give one example of magnetic storage. [1] (ii) Give one example of optical storage. [1] (iii) Identify which type of storage would be the most suitable for use in a web server and justify your choice. Type of storage Justification [3] (c) Describe the operation of USB flash memory and how it stores data. [3]

2 Jolene displays videos on her website. She uses lossy compression to reduce the file size of the videos. (a) Describe how lossy compression reduces the file size of the videos. [3] (b) State two reasons why Jolene would use lossy rather than lossless compression for the videos. Reason 1 Reason 2 [2]

2 Magda has a mobile telephone. She uses the touch screen on her telephone to send emails to her customers. The touch screen breaks, stopping Magda from using it to type her emails. (a) Identify one other input device that would be built into the mobile telephone that Magda could use to send an email to her customers. [1] (b) The touch screen operates by using the conductive properties of the object that is used to touch the screen. State whether the touch screen is a resistive, capacitive or infra-red touch screen. [1] (c) Magda is listening to music on her mobile telephone when she receives a telephone call. A signal is sent within the telephone to stop the music and output that a call has been received. Give the name of this type of signal. [1]

2 A train company wants to install a self-service ticket machine system for its train stations. When the customer has purchased their tickets, the machine will provide a paper ticket. (a) One output device that is used in the ticket machine is a display screen. Identify one other output device that is used in the ticket machine system. [1] (b) The train company does not want users to use a keyboard or a mouse to enter their data, when buying a ticket. The company is worried that they may be stolen or get too dirty. Identify one other input device that would be suitable for use in the ticket machine system, to allow users to enter their data. [1]

2 A sports stadium has an electronic counter that counts each person that enters the stadium. The count is stored as binary in a 16-bit register. A denary value of the count is displayed on a screen at the entrance. (a) The screen currently displays: 0 0 7 1 Give the binary value that is stored in the register to display the count shown. Binary value: Working space [2] (b) More people enter the sports stadium and the screen now displays: 0 2 5 7 Give the binary value that is stored in the register to display the count shown. Binary value: Working space [2] (c) After everyone has entered the stadium, the register stores the binary value: 0000001000000100 Show what the screen will display when this binary value is stored. Display: [1] Working space (d) Sensors are used at the entrance to count the number of people entering the stadium. (i) Identify two sensors that could be used to count the number of people entering the stadium. Sensor 1 Sensor 2 [2] (ii) Tick (3) one box to show if a sensor is an example of an input device, storage device or output device. Device Tick (✔) input storage output [1]

3 The given table shows the name or description of four devices. The table is incomplete. Complete the missing device names and descriptions. Device name Description Uses either thermal bubble or piezoelectric technology Actuator Uses thousands of tiny mirrors that can move very quickly to create an image Mouse [4]

3 A firewall can be used to help keep the data secure that is stored on a computer. (a) The given paragraph describes how the firewall operates to help keep the data secure. Complete the paragraph using the most appropriate terms from the given list. Not all of the terms on the list need to be used. • Accept • Criteria • Hacking • Input • Network • Outgoing • Output • Processor • Reject • Software • Store • Storage A firewall can be or hardware based. It monitors traffic between the computer and the The user sets for the traffic. The firewall will or the traffic based on this. It can help prevent and malicious software that could be a threat to the security of the data. [6] (b) Identify three other methods that could be used to keep the data secure. Method 1 Method 2 Method 3 [3]

3 Consider the logic statement: X = ((((NOT A AND B) OR C) AND B) NOR (B OR C)) (a) Draw a logic circuit to represent the given logic statement. Do not attempt to simplify the statement. All logic gates must have a maximum of two inputs. A X B C [6] (b) Consider the completed truth table for the given logic statement. Row number A B C Working space X 1 0 0 0 1 2 0 0 1 1 3 0 1 0 1 4 0 1 1 0 5 1 0 0 1 6 1 0 1 0 7 1 1 0 1 8 1 1 1 1 There are four errors in the truth table in the output (X) column. Identify the four incorrect outputs. Write the row number to identify each incorrect output. Row Row Row Row [4]

3 An optical mouse is a type of input device that can be used to input data into a computer system. (a) Complete the paragraph about the operation of an optical mouse, using the most appropriate terms from the given list. Not all terms need to be used. • Ball • Battery • LCD • LED • Lens • Magnifies • Matrix • Microswitch • Photoelectric • Photographic • Reduces • USB An optical mouse shines an from the bottom of the mouse onto a surface. Light bounces straight back from the surface into a cell. This has a that the reflected light to allow detection of smaller movements. When a button on the mouse is clicked, a is pressed. A connection is used to carry the data to the computer. [6] (b) Identify two other input devices that can be used to enter data into a computer. 1 2 [2]

3 Five statements are given about the error-checking methods checksum, check digit and parity check. (a) Tick (3) to show whether each statement applies to checksum, check digit or parity check. Some statements may apply to more than one error-checking method. Check Parity check Statement Checksum digit (3) (3) (3) uses an additional bit to create an odd or even number of 1s checks for errors on data entry compares two calculated values to see if an error has occurred will not detect transposition errors sends additional values when data is transmitted from a computer to another [5] (b) Identify one other error-checking method. [1]

3 (a) Six statements are given about methods of data transmission. Tick (✓) to show if each statement applies to serial simplex, parallel simplex, parallel half-duplex or serial duplex data transmission. Some statements may apply to more than one data transmission method. Serial simplex Parallel simplex Parallel half-duplex Serial duplex Statement (✓) (✓) (✓) (✓) bits are transmitted along a single wire data is transmitted in both directions it is only suitable for distances less than 5 metres bits from the same byte are transmitted one after the other data may not arrive in the correct sequence data is transmitted in both directions, but only one direction at a time [6] (b) A Universal Serial Bus (USB) connection can be used to transmit data from a mobile device to a computer. Give three benefits of using a USB connection for this purpose. Benefit 1 Benefit 2 Benefit 3 [3]