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CompSci: Component 2 > 2.6 The Operating System > Flashcards

2.6 The Operating System Flashcards

1
Q

What is scheduling?

A

The method by which the processor allocates its time into slices for specific jobs. The scheduler decides which job will be processed next.

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2
Q

Where is scheduling used?

A

Used in multi-programming, multi-tasking and multi-access operating systems.

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3
Q

Why are job priorities relevant to scheduling?

A

They are used to enable important data to be pushed forward in the line and less important data to fall back and processed after.

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4
Q

Why is it important to take care when allocating job priorities?

A

Care must be taken when allocating job priorities because if a job is constantly moved back, it may never get processed.

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5
Q

What concept can be utilised to stop possible starvation or indefinite blocking of data when it is moved back in the schedule?

A

Aging can be used where the priority of a low-priority task is incremented as the waiting time increases.

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6
Q

What three states can jobs have in a scheduled system?

A

Ready - The process is waiting to be executed
Running - The process is being executed by the processor
Blocked - The process is waiting for some event (such as input or output)

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7
Q

What is Deadlock in terms of scheduling?

A

Deadlock occurs when processes are blocked by another process which is also blocked. This can mean all the processes are waiting for data from each other.

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8
Q

What is a Single-User (Standalone) operating system?

A

Only allows one user to access the programs/data at a time.
If the system is also Single-Tasking then only one program can be executed at a time.

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9
Q

What is a Multi-User (Multi-Access) operating system?

A

Allows different users to use the processing capabilities of the computer at the same time. It is similar to Multi-Tasking however the emphasis is on different users, not different programs.

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10
Q

What is a Multi-Programming operating system?

A

A system where multiple jobs are processed simultaneously therefore they are typically used in large commercial systems which need to cope with multiple processes daily.

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11
Q

How does Multi-Programming benefit the CPU?

A

It is used to ensure the most efficient use of the CPU whilst also preventing it from becoming idle whilst waiting for an input/output.

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12
Q

How is scheduling utilised in Multi-Programming operating systems?

A

The operating system implements scheduling by moving jobs in and out of memory and allowing each job a pre-determined time-slice to access the CPU.

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13
Q

What is a Time-Slice?

A

The amount of time allocated to each job by the operating system

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14
Q

What is Partitioning?

A

The division of computer memory for different jobs. This allows more than one job to be resident in the memory at the same time.

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15
Q

What is Real-Time Processing?

A

A mode of operation where data received is immediately processed and stored data is instantly updated. A computer used for real-time processing is dedicated and does nothing else.

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16
Q

Name 3 examples of Real-Time Processing.

A

Flight Simulators
Computer Guided Missiles
Air Traffic Control

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17
Q

What is Real-Time Transaction?

A

An online system where individual discrete transactions are processed as they occur. When a transaction is received, the data stored is updated immediately.

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18
Q

How could Real-Time Transactions be utilised in a booking system?

A

It would ensure that no two people make the same booking as the system is always up-to-date.

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19
Q

What is important to do after a process has finished? (After partitioning)

A

It is important to release the partition so that the area of memory can be reused by another process.

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20
Q

What could happen to the memory after a large number of jobs have been processed?

A

The memory may become fragmented, suggesting it is made up of lots of little ‘free’ areas rather than one large area. This can slow down the operation of the computer system.

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21
Q

What is the main advantage of partitioning?

A

It allows for separate processes to be allocated to partitioned areas of main memory instead of loading it into memory one at a time and significantly slowing down processing speeds.

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22
Q

What are the two memory management techniques for partitioning?

A

Contiguous - Each executing process must be loaded entirely into one partition of main memory.

Non-contiguous - Processes can be divided into different parts and fill the space in main memory (Without having to be stored in the same place)

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23
Q

What is an advantage and disadvantage of non-contiguous as a memory management technique?

A

It reduces memory wastage as it fills the gaps in the memory but it slows down the execution time as address translation is longer.

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24
Q

What is Fixed Partitioning?

A

Partitions of memory are fixed in size therefore, a process could be loaded in of equal or greater size and will just be confined to that space.

25
Q

What are four potential consequences of fixed partitioning?

A

Internal/External Fragmentation - Main memory use is inefficient as any program no matter how small occupies an entire partition.

Limited process size - Processes larger than the partition cannot be accommodated for.

Limitation on degree of multiprogramming - Number of processes cannot be greater than the number of partitions in memory.

26
Q

What is variable partitioning?

A

System which divides memory into non-overlapping variable sizes.

The number of partitions is fixed but the size varies.

More flexible as small processes are allocated to small partitions and large processes are allocated to larger partitions.

27
Q

What is dynamic partitioning?

A

Partitions are not made before execution, they are created during the run-time according to the processes’ needs so the partition matches in size.

The number of partitions is not fixed as it depends on the number of incoming processes and size of main memory.

28
Q

What are three advantages of dynamic partitioning?

A

No Internal fragmentation.
No restriction on degree of multiprogramming.
No restriction of process size.

29
Q

What are two disadvantages of dynamic partitioning?

A

More difficult to implement as it requires allocation of memory during run-time.
External Fragmentation may still arise as memory can become free after processes are finished however, once you are during the run-time of the program, partitions cannot be changed.

30
Q

What is the difference between internal and external fragmentation?

A

Internal fragmentation occurs when small processes are assigned large partitions therefore fragments are created.

External fragmentation is the opposite because it occurs when the assigned partition is too small for the process so fragments are formed where the process could be stored instead.

31
Q

What is an operating system?

A

A set of programs which manage the operations of a computer.

32
Q

What is booting?

A

When a computer is first switched on, the OS is transferred from disc to memory.
This is controlled by the BIOS located in ROM.

33
Q

What is the Kernel?

A

The central component of the operating system which provides the link/interface between the software and the hardware.

34
Q

What are the 4 main responsibilities of the Kernel?

A

Process Management - Allocates processor time.
Memory Management - Allocates memory to processes.
Device Management - Processed outputs are handled using device drivers.
Interrupt Handling - Enables the CPU to process higher priority events.

35
Q

What are the purpose of utility programs on an operating system?

A

File management, editing of files, reorganising disk space (Defragmentation), backups, encryption

36
Q

What is Spooling?

A

Items are sent to a hardware device and stored in a queue for processing.
Uses input and output buffers to compensate for the difference in speed between devices.

37
Q

What is Polling?

A

The sequential checking of jobs so each job gets its appropriate share of time.
Also can be used to check the status of each user.

38
Q

Why does the operating system periodically check the progress of jobs?

A

To allow jobs to re-join the runnable queue when input/output is completed.

39
Q

What is Batch Processing?

A

One or more programs which are submitted to the computer as a ‘job’ are put into a queue without interaction between the user and the computer.

40
Q

What is a Batch Operating System?

A

Processes are carried out with no user interaction.
Errors are stored in a file for later use and not dealt with as they occur.

41
Q

What is an advantage of a Batch Operating System?

A

Batch processing may avoid using computer resources at times when demand is high/off-peak.

42
Q

What is Multi-Tasking?

A

Occurs when more than one task or application is available to the user at the same time (The operating system switches quickly between one task to another).

43
Q

What is Backing Storage?

A

Refers to any storage that isn’t the main memory.
Can be referred to as secondary storage - Hard drive is the most common type.

44
Q

How is data on a secondary storage medium stored?

A

It is stored in blocks where the size depends on the type of media in which it is formatted.

45
Q

What are four examples of File Attributes?

A

Read-Only
Hidden
System
Archive

46
Q

What is a Command Driven Interface?

A

A user has to type in a command and tailor it to suit the requirements. (e.g. DOS)

47
Q

What is a disadvantage of a Command Driven Interface?

A

Users will have to learn the commands and spell them correctly every time.

48
Q

What is a Menu Driven Interface?

A

Options are displayed as a Hierarchy of menus, selecting one option leads to another menu.

49
Q

What is a GUI?

A

A graphical user interface includes small icons which are used to represent different selections.
Sometimes called a WIMP environment (Windows, Icons, Menus, Pointers)

50
Q

What are three advantages of a GUI?

A

No great level of IT needed.
Easily recognisable and understandable.
No need to learn any commands.

51
Q

What is an interrupt?

A

A signal generated by a device or software, which may cause a break in the execution of the current routine.

52
Q

What are 6 potential causes of interrupts?

A

Run time error.
Security Update.
Power Failure.
User request.
Printer sends interrupts to Spooling system.
Input/Output process.

53
Q

What is Interrupt Handling?

A

Once an interrupt occurs, the current state of the program is suspended.
This procedure deals with the interrupt and ensures the program resumes from its original point.

54
Q

Why are interrupts allocated different priority levels?

A

So if two or more interrupts occur at the same time, the computer knows which one to deal with first.

55
Q

What is an example of a low priority and a high priority interrupt?

A

‘Printer Out of Paper’ would be low priority and Impending data loss would be of high priority.

56
Q

What is Buffering?

A

Buffering is using an area of memory to store data while transferring to/from a peripheral.

57
Q

Why is a buffer used?

A

To compensate for different speeds of devices.
Buffering in a printer.
Single Buffering in a keyboard.
Internet Downloads.

58
Q

Why is Double Buffering used?

A

Whilst one buffer is being emptied another can be filled to avoid waiting for data to transfer and make the process more efficient.

CompSci: Component 2 (7 decks)

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