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Computer Science > Operating Systems > Flashcards

Operating Systems Flashcards

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1
Q

Operating system

A

Core software that controls how the computer operates

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2
Q

Purpose of Operating System

A
  • Control the hardware of the computer system. e.g. hard drive
  • Manage software, in terms of loading (and unloading) into main memory.
  • Provide security, such as user name and password control.
  • Provide an user interface
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3
Q

Parts of an Operating System

A

The KERNEL
The DEVICE DRIVERS
The USER INTERFACE
The SYSTEM UTILITIES

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4
Q

The Kernel

A
  • Loading / Unloading applications from memory
  • Memory management
  • File management
  • Data security
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5
Q

Device drivers

A

Enables the operating system to control and communicate with the device.

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6
Q

User Interface

A

Allows a person to interact with the computer.

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7
Q

System Utilities

A

All the basic facilities that run in the background without user interaction
- File management services
- Anti-virus utility
- File compression utiity

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8
Q

Reason for memory management

A

Every computer has a limited amount of memory. Memory is a limited resource so it has to be managed.Task of memory manager.

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9
Q

Segmentation

A
  • Memory is split up into segments
  • Segments can vary in size
  • Uses logical divisons
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10
Q

Paging

A
  • Memory is split into equal size pages
  • Pages are swapped between main and virtual memory
  • Uses physical divisions
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11
Q

Disk thrashing.

A

As more pages are swapped, eventually more time is spent swapping pages than on processing the data. This is called disk thrashing.

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12
Q

Memory leaks

A

A well-written program will flush its data away once it no longer needs it and declares memory as free.
A badly-written program will not flush its data properly. The memory remains unavailable, locked up.

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13
Q

Scheduling

A

Task of allocating CPU processor time amongst all running programs.

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14
Q

Purpose of scheduling

A
  • Processes as many tasks as possible in a given time
  • Makes maximum use of CPU time
  • It will try to minimise the delay between when the user requests something to be done and when that task is completed.
  • Makes maximum use of resources
  • Ensure that no task is left uncompleted for too long
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15
Q

Round Robin

A
  • Eeach process is give time slice
  • If completed next process is loaded
  • If not repeats until is completed
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16
Q

First come first served

A
  • Process in the order they enter the queue
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17
Q

Shortest job first

A
  • The queue is ordered by the amount of processor time needed
  • Shortes Jobs are completed first
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18
Q

Shortest Time Remaining

A
  • The queue is based on the timeleft to completion
  • Jobs with the least time needed are completed first
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19
Q

Multi-level feedback queues

A
  • Uses multiple queues, each with a different priority
20
Q

Polling

A

CPU to keep checking devices or events to see if they need attention. For instance a file may need to be sent to the printer.

21
Q

Interrupt

A

It is a signal for the CPU to stop what it is doing and instead carry out the interrupt task. Once the task is complete, the CPU goes back to what it was doing.

22
Q

Interrupt Service Routine

A
  • At the end of FDE cycle the interrupt register is checked
  • If there is an interrupt with a hiher priority than the current task
    Contetns of registers copied into stack
    ISR is load into RAM
    Flag is set interrupt begun
    Flag is reset when ISR finished
    Reapeats until no interrupts exist
23
Q

Types of Operating System

A

Multi-tasking
Multi-user
Embedded
Distributed
Real-time
Batch

24
Q

Multi-tasking operating System

A
  • Allows multiple taskts to be completed simultaniously
  • Uses time slicing to switch between aplplications
25
Q

Multi-user operating system

A
  • Several users can use a single computer
  • A scheduling algorithm alllocates processor time
26
Q

Distributed operating system

A
  • Runs across several devices
  • Spreads taskloads across multiple computers
27
Q

Real time operating system

A
  • Performs task within a guaranteed time frame
28
Q

Embedded operating system

A
  • Built for a specific task
  • Limited functionality
  • Less resource intensive
29
Q

BIOS

A

Basic Input Output System
- Runs when a computer turns on
- Runs tests then loads the OS into memory
- Power On Self Test makes sure all hardware is connected anf functional
- Tests the CPU, Memory and external devices

30
Q

Virtual Machine

A
  • A software implementation of the computer
  • Can execute intermediate code
  • Takes longer to execute
  • Used to emulate the machine
31
Q

Utilities

A

Application that has a very specific task to carry out

32
Q

Open source software

A
  • Source code provided
  • No license required
33
Q

Closed source software

A
  • Need a license to use
  • Source code not available
  • Protected by Copyright
34
Q

Open source Pros / Cons

A
  • Free
  • Source code is publicly available
  • Technical support limited
  • Not well dcumented
  • Less secure
  • Variable quality code
35
Q

Closed source Pros / Cons

A
  • More secure
  • Regular updates
  • More polished
  • Well documented and supported
  • More expensive
  • Code can not be changed
36
Q

Translator

A

Converts one computer language into another. Usually it translates source code into machine code.
- Compiler
- Interpreter
- Assembler

37
Q

Compiler

A
  • Translates code in one go
  • Compilation process is longer
  • Produces platform specific code
  • Complied code can be run without a translator
38
Q

Interpreter

A
  • Translates and executes code line by line
  • Will error if line contains an error
  • Slower to run than complier
  • Useful for testing
39
Q

Assembler

A
  • Platform specific low level code
  • Translates assembly code to machine code
  • 1 line of assembly code = 1 line of machine code
40
Q

Software development​ Stages

A

Analysis​
Design​
Implementation (programming, testing and installation)​
Evaluation​
Maintenance​

41
Q

Waterfall Model Pros / Cons

A

Pros
- Simple to understand and use​
- Each stage separated and documented
- Project easy to manage
- Works well for smaller projects

Cons
- There is not much user involvement after the Analysis stage,
- No software is produced until late in ​the cycle​
- Too late to make changes

42
Q

Spiral Model​

A
  • Analysis
  • Design
  • Implementation
  • Evaluation
43
Q

Spiral Model Pros / Cons

A

Pros
- Well-defined steps make the project easy ​to manage​
- Software is produced at an early stage
- User gives feedback on each prototype
- Functionality can be added during the process​
- End result is more likely to be what the ​user wants

Cons
- Time-consuming so the finished product takes longer to develop​
- More costly to develop because of the time involved​
- Not suitable for smaller projects​

44
Q

Agile model​

A
  • Software is developed in rapid incremental cycles​
  • Each version builds on previous functionality​
  • Each version is thoroughly tested before release​
  • Good for small, time-critical projects​
  • Limited planning is needed to get started
45
Q

Agile model​ Pros / Cons

A

Pros
- Rapid, continuous delivery of useful software leads to customer satisfaction​
- Customers, developers and testers constantly interact
- Working software is delivered frequently
- Software is easily adapted to changing circumstances​
- Even late changes in requirements can ​be implemented

Cons
- Lack of emphasis on necessary design and documentation
- The project can fail to deliver if the customer is not clear about the final outcome​
- Not suitable for novice programmers

Computer Science (3 decks)

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