Purposes of an Operating System (OS) (Cambridge (CIE) A Level Computer Science): Exam Questions

The kernel is the central component of an Operating System (OS).

Outline how the kernel of an OS acts as an interrupt handler.

(i) State what is meant by the term multi‑tasking in an Operating System.

(1)

(ii) Describe how multi‑tasking is implemented in an Operating System.

(2)

A student buys a new computer.

State one benefit to the student of a user interface and give an example.

Benefit

Example

Two of the process states are the running state and the ready state.

Identify one other process state.

Outline conditions under which a process could change from the running state to the ready state.

Outline the reasons why an operating system may need to use virtual memory.

Explain the circumstances in which disk thrashing could occur.

An operating system receives an interrupt that has a higher priority than the process that is currently running.

Identify:

• the mode that the system enters to handle the interrupt

• the table that is consulted to find the Interrupt Service Routine (ISR) for this type of interrupt.

A student copies a photo from the hard disk of a computer to a USB flash drive. The student does this by dragging the icon for the photo onto the icon for the flash drive.

The user interface hides the complexities of the hardware from the student.

Identify two complexities of the hardware that are hidden from the student during this task.

An operating system uses interrupt handling to manage low-level scheduling.

Process A is in the running state and process B is in the ready state. An interrupt is generated. The interrupt has a higher priority than process A.

Explain how the kernel handles this interrupt so that process A stops running and can later continue from the point at which it stopped.

An operating system (OS) gives every process a process state.

Complete the table by writing the name of the process state that matches each description. The first row has been done for you.

A process is in the running state. It needs to read data from a file stored on a hard disk before it can continue.

Describe the changes of process state that happen from this point until the process is executed by the processor again.

A computer has a single processor. A user has three programs open at the same time:

• a music player

• a word processor

• a program that is copying a large file to a USB flash drive.

The user believes that all three programs are running at the same time.

Explain how the operating system uses the running, ready and blocked process states to make it appear that all three programs are running at the same time.

A student's computer has a processor with a single core. The student has a web browser, a music player and a spreadsheet open at the same time. The student also sends a long document to a printer.

Explain how the Operating System (OS) maximises the use of the computer's resources in this situation.

Your answer must refer to the processor, main memory and the printer.

A file server has a single processor. Its operating system has many processes to run.

Give two reasons why the operating system needs to schedule these processes.

A computer is running several programs at the same time, including a web browser, a word processor and a music player.

Explain why the operating system needs to carry out memory management while these programs are running.

A computer is used for two tasks at once. A user is typing a report in a word processor. At the same time, a video-editing program is producing a long video file, which needs a lot of processor time. The video-editing process joined the queue for the processor first.

Explain why round robin scheduling is more suitable than first come first served scheduling in this situation.

Paging is one of the techniques an operating system uses for memory management.

Describe what is meant by paging.

A program is stored on secondary storage. The operating system uses paging when the program is run.

Describe how paging is used to manage main memory while the program is running.

A computer uses paging. The table shows eight blocks of main memory. All the blocks are the same size.

A running program needs three more of its pages to be loaded from secondary storage. There is no area of main memory where three free blocks are next to each other.

Explain how paging allows all three pages to be loaded into main memory.

Four processes are waiting in the queue for the processor. They joined the queue in the order shown. No other processes join the queue.

Throughput is the number of processes completed in a given amount of time.

Use the information in the table to explain why shortest job first scheduling gives a higher throughput than first come first served scheduling for these processes.

A computer uses segmentation for memory management.

Identify the two values that make up an address in a program's logical address space when segmentation is used.

Paging and segmentation are both used in memory management.

Complete the table to show one difference between paging and segmentation for each feature.

A computer has 8 GiB of RAM. A user starts a program that needs 12 GiB of memory for its code and data. The operating system uses segmentation and virtual memory.

Explain how segmentation and virtual memory allow this program to run on the computer.

Describe what is meant by virtual memory.

A computer uses paging and virtual memory. The RAM is full. A running program needs a page that is currently held in virtual memory.

Describe how the operating system replaces a page in RAM so that the program can use the page it needs.

A computer uses virtual memory stored on a hard disk drive. A technician records how the computer spends its time as more programs are opened.

(i) Using the table, state the smallest number of programs open at which the computer has reached the thrash point. Give a reason for your answer.

(2)

(ii) Explain why the percentage of time spent swapping pages increases as more programs are opened.

(3)