Explain why a personal computer (PC) needs an operating system (OS). One of the tasks carried out by the OS is the management of the use of the processor. Name and describe two other management tasks that the OS performs. A user has the following issues with the use of their personal computer (PC). For each case, state the utility software which should provide a solution. The user wants to send a large file as an attachment to an email. The user knows that the recipient’s Internet Service Provider (ISP) has a limit of 2MB for file attachments. Utility software solution: The user is writing a book and is worried that the document files could get damaged or deleted. Utility software solution: The computer has recently been slow to load large files. The user has deleted a large number of small files to try to solve the problem. A friend has advised that there is a procedure which should be regularly carried out to reorganise file storage on the hard disk. Utility software solution: The user clicked on an attachment in an unsolicited email. Since then, the computer has shown some unexplained behaviours. Utility software solution:

9608_s17_qp_12

THEORY

2017

Paper 1, Variant 2

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Aaron uses a desktop computer to do school work. Aaron has a mouse and keyboard that he can use as input devices and a monitor as an output device. Identify two additional input devices Aaron could use with his desktop computer. Identify two additional output devices Aaron could use with his desktop computer. Aaron needs to store a large number of applications and data on his computer. He needs at least 50GB of secondary storage space. Identify one internal secondary storage device for Aaron’s computer. Describe the internal operation of a trackerball mouse. Aaron’s computer has an operating system (OS). The OS manages the running processes and provides a user interface. Describe these OS management tasks. Process management Provision of a user interface Aaron’s computer has a virus checker and backup software. Describe these utility programs. Virus checker Backup software Aaron creates a web page using JavaScript code and HTML tags. Describe how the JavaScript code is translated using an interpreter.

9608_w19_qp_11

THEORY

2019

Paper 1, Variant 1

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Mahmoud is developing a new application, MyApp, that needs to work with three different operating systems (OS1, OS2 and OS3). He has decided to use virtual machine software to test MyApp with these three different operating systems. The diagram shows MyApp running on three virtual machines. MyApp MyApp MyApp OS1 OS2 OS3 Virtual machine software OS4 Hardware Describe the roles of the four operating systems (OS1, OS2, OS3 and OS4) shown in the diagram. Describe the role of the virtual machine software in the testing of MyApp. Explain one benefit and one drawback of this approach to testing MyApp. Benefit Drawback

9608_w20_qp_32

THEORY

2020

Paper 3, Variant 2

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A computer system is used to manage some of the functions in a vehicle. The vehicle has a number of sensors and actuators. One sensor is used to monitor the moisture on the screen. If the moisture exceeds a pre-set value, the windscreen wiper motor turns on automatically. The software used in the computer system is dedicated to the sensor management functions. When the system starts, the software runs some initial tasks. It then loops continuously until the system is switched off. State the name given to the type of system described. Explain your answer to part . Within the software loop, the value of each sensor is read in turn. The value read from the sensor is then processed. State two drawbacks with this method of reading and processing sensor data. Drawback 1 Drawback 2 An alternative method of reading and processing sensor data is to use interrupts. Each sensor is connected so that it can send an interrupt signal to the processor if its value changes. On receipt of an interrupt signal, the processor carries out a number of steps as shown in the following diagram. Interrupt Return to task 1. Disable interrupts 6. Enable interrupts 2. Save current task 3. Identify source of 4. Jump to Interrupt Service Routine interrupt 5. Restore task State the purpose of step 1. State the purpose of step 6. Explain how the current task is saved in step 2. State two benefits of using interrupts to read and process the sensor data. Benefit 1 Benefit 2 The interrupt handler in step 3 has to test each bit of a 16-bit register to discover the source of the interrupt. The contents of the 16-bit register are loaded into the 16-bit accumulator: Accumulator Bit: An instruction is required to achieve the following: • If bit 9 is zero, set the accumulator to zero. • If bit 9 is one, set the accumulator to a non-zero value. Write this instruction using an appropriate bitwise operation.

9608_s17_qp_31

THEORY

2017

Paper 3, Variant 1

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A computer system is used to manage some of the functions in a vehicle. The vehicle has a number of sensors and actuators. One sensor is used to monitor the moisture on the screen. If the moisture exceeds a pre-set value, the windscreen wiper motor turns on automatically. The software used in the computer system is dedicated to the sensor management functions. When the system starts, the software runs some initial tasks. It then loops continuously until the system is switched off. State the name given to the type of system described. Explain your answer to part . Within the software loop, the value of each sensor is read in turn. The value read from the sensor is then processed. State two drawbacks with this method of reading and processing sensor data. Drawback 1 Drawback 2 An alternative method of reading and processing sensor data is to use interrupts. Each sensor is connected so that it can send an interrupt signal to the processor if its value changes. On receipt of an interrupt signal, the processor carries out a number of steps as shown in the following diagram. Interrupt Return to task 1. Disable interrupts 6. Enable interrupts 2. Save current task 3. Identify source of 4. Jump to Interrupt Service Routine interrupt 5. Restore task State the purpose of step 1. State the purpose of step 6. Explain how the current task is saved in step 2. State two benefits of using interrupts to read and process the sensor data. Benefit 1 Benefit 2 The interrupt handler in step 3 has to test each bit of a 16-bit register to discover the source of the interrupt. The contents of the 16-bit register are loaded into the 16-bit accumulator: Accumulator Bit: An instruction is required to achieve the following: • If bit 9 is zero, set the accumulator to zero. • If bit 9 is one, set the accumulator to a non-zero value. Write this instruction using an appropriate bitwise operation.

9608_s17_qp_33

THEORY

2017

Paper 3, Variant 3

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The following diagram shows how applications X, Y and Z can run on a virtual machine system. Application X Application Y Application Z Guest operating system 1 Guest operating system 2 Virtual machine software / virtual machine monitor Host operating system Hardware The virtual machine software undertakes many tasks. Describe two of these tasks. Task 1 Task 2 Explain the difference between a guest operating system and a host operating system. A company uses a computer as a web server. The manufacturer will no longer support the computer’s operating system (OS) in six months’ time. The company will then need to decide on a replacement OS. The company is also considering changing the web server software when the OS is changed. Whenever any changes are made, it is important that the web server service is not disrupted. In developing these changes, the company could use virtual machines. Describe two possible uses of virtual machines by the company. Use 1 Use 2 The web server often has to handle many simultaneous requests. The company uses a virtual machine to test possible solutions to the changes that they will need to make. Explain one limitation of this approach.

9608_s16_qp_31

THEORY

2016

Paper 3, Variant 1

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The following diagram shows how applications X, Y and Z can run on a virtual machine system. Application X Application Y Application Z Guest operating system 1 Guest operating system 2 Virtual machine software / virtual machine monitor Host operating system Hardware The virtual machine software undertakes many tasks. Describe two of these tasks. Task 1 Task 2 Explain the difference between a guest operating system and a host operating system. A company uses a computer as a web server. The manufacturer will no longer support the computer’s operating system (OS) in six months’ time. The company will then need to decide on a replacement OS. The company is also considering changing the web server software when the OS is changed. Whenever any changes are made, it is important that the web server service is not disrupted. In developing these changes, the company could use virtual machines. Describe two possible uses of virtual machines by the company. Use 1 Use 2 The web server often has to handle many simultaneous requests. The company uses a virtual machine to test possible solutions to the changes that they will need to make. Explain one limitation of this approach.

9608_s16_qp_32

THEORY

2016

Paper 3, Variant 2

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The following diagram shows how applications X, Y and Z can run on a virtual machine system. Application X Application Y Application Z Guest operating system 1 Guest operating system 2 Virtual machine software / virtual machine monitor Host operating system Hardware The virtual machine software undertakes many tasks. Describe two of these tasks. Task 1 Task 2 Explain the difference between a guest operating system and a host operating system. A company uses a computer as a web server. The manufacturer will no longer support the computer’s operating system (OS) in six months’ time. The company will then need to decide on a replacement OS. The company is also considering changing the web server software when the OS is changed. Whenever any changes are made, it is important that the web server service is not disrupted. In developing these changes, the company could use virtual machines. Describe two possible uses of virtual machines by the company. Use 1 Use 2 The web server often has to handle many simultaneous requests. The company uses a virtual machine to test possible solutions to the changes that they will need to make. Explain one limitation of this approach.

9608_s16_qp_33

THEORY

2016

Paper 3, Variant 3

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A computer at a remote weather station is performing three tasks: • measuring and recording the temperature every 10 seconds • measuring and recording the wind speed every 10 seconds • sending the previous day’s temperature and wind speed readings to a scientist at another location via the Internet. The operating system is managing the multitasking of these tasks. At one point in time: • the temperature measuring and recording task is idle • the wind speed is being recorded • the task to send the previous day’s temperature and wind speed readings is waiting for an internet connection. Identify the process state for each task. Give a reason why each task is in that process state. Temperature measuring and recording process state Reason Wind speed measuring and recording process state Reason Sending process state Reason The weather station computer uses an operating system. Explain how this operating system uses interrupts to schedule the measuring and recording tasks.

9608_s20_qp_31

THEORY

2020

Paper 3, Variant 1

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A computer at a remote weather station is performing three tasks: • measuring and recording the temperature every 10 seconds • measuring and recording the wind speed every 10 seconds • sending the previous day’s temperature and wind speed readings to a scientist at another location via the Internet. The operating system is managing the multitasking of these tasks. At one point in time: • the temperature measuring and recording task is idle • the wind speed is being recorded • the task to send the previous day’s temperature and wind speed readings is waiting for an internet connection. Identify the process state for each task. Give a reason why each task is in that process state. Temperature measuring and recording process state Reason Wind speed measuring and recording process state Reason Sending process state Reason The weather station computer uses an operating system. Explain how this operating system uses interrupts to schedule the measuring and recording tasks.

9608_s20_qp_33

THEORY

2020

Paper 3, Variant 3

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