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Computer Science > Unit 2 : Systems Software > Flashcards

Unit 2 : Systems Software Flashcards

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1
Q

What is an operating system

A

● A collection of programs that provide an interface between the user and computer
● Provide the following features:

○ Memory management
○ Resource management eg. scheduling
○ File management
○ Input/ Output management
○ Interrupt management
○ Utility software
○ Security
○ User interface

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2
Q

What does the computer do when it doesn’t have enough memory

A

● Main memory is often not large enough to store all of the programs being used.
● Paging, segmentation and virtual memory are techniques used by the operating system to ensure memory is shared effectively by programs.

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3
Q

What is paging

A

● Memory is split up into equal-sized sections known as pages.
● Pages are swapped between main memory and the hard disk as needed.

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4
Q

What is segmentation

A

● Memory is split up into logical sized divisions, called segments.
● Segments vary in size
● Segments represent the structure and logical flow of the program.

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5
Q

What is virtual memory

A
  • A section of the hard drive acts as RAM when the space in main memory is insufficient to store programs being used.
  • Sections of programs not currently being used are temporarily moved into virtual memory through paging.
  • This frees up memory for other programs in RAM.
  • The key issue with using these techniques is disk thrashing, when the computer ‘freezes’ due to pages being swapped too frequently between the hard disk and main memory.
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6
Q

What are interrupts

A

● Signals generated by software or hardware to indicate to the processor that a process needs attention.
● Interrupts have different priorities and this is considered when allocating processor time.
● They are stored within an abstract data structure called a priority queue in an interrupt register.

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7
Q

What is the interrupt service routine

A

● Processor checks the interrupt register at the end of each Fetch-Decode-Execute cycle.

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8
Q

What happens when there is an interrupt with higher priority to the current process

A

● If there is an interrupt exists with a higher priority to the current process

○ The current contents of the registers in the CPU are transferred into a stack.
○ The relevant interrupt service routine (ISR) is loaded into RAM.
○ A flag is set to signal the ISR has begun.
○ The flag is reset once the ISR has finished.
○ This process is repeated.

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9
Q

What happens If there are no interrupts with a higher priority to the current process

A

● If there are no interrupts with a higher priority to the current process

○ The contents of the stack are popped back into the registers
○ Fetch-Decode-Execute cycle resumes

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10
Q

What is scheduling

A

● Operating system ensures all sections of programs being run (known as ‘jobs’) receive a fair amount of processing time using scheduling.

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11
Q

what is pre-emptive scheduling

A
  • Jobs are actively made to start and stop by the operating system. For example: Multilevel Feedback Queues, Shortest Remaining Time, Round Robin
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12
Q

What is non-preemptive scheduling

A
  • Once a job is started, it is left alone until it is completed.
  • For example: First Come First Served, Shortest Job First
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13
Q

What is the round robin algorithm

A
  • Each job is given a section of processor time - a time slice - within which it runs.
  • Once each job in the queue has used its first time slice, they are given another slice of processor time until a job has been completed
  • Completed jobs are removed from the queue.
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14
Q

What are the advantages of the round robin algorithm

A
  • All jobs will eventually be attended to
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15
Q

What are the disadvantages of the round robin algorithm

A
  • Longer jobs will take a much longer time for completion
  • Round robin does not take into account job priority or urgency
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16
Q

What is the first come first served algorithm

A
  • Jobs are processed in chronological order by which they entered the queue
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17
Q

What are the advantages of the first come first served algorithm

A
  • Straightforward to implement
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18
Q

What are the disadvantages of the first come first served algorithm

A
  • Does not take into account job priority or urgency
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19
Q

What is the multilevel feedback queue

A
  • This makes use of multiple queues, each which is ordered based on a different priority.
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20
Q

What are the advantages of the multilevel feedback queue algorithm

A
  • Takes into consideration different job priorities
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21
Q

What are the disadvantages of the multilevel feedback queue algorithm

A
  • Difficult to implement
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22
Q

What is the shortest job first algorithm

A
  • The queue storing jobs to be processed is ordered according to the time required for completion, with the longest jobs being serviced at the end.
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23
Q

What are the advantages of the shortest job first algorithm

A
  • Suited to batch systems, as waiting time is reduced
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24
Q

What are the disadvantages of the shortest job first algorithm

A
  • Requires processor to calculate how long each job will take
  • Processor starvation if short jobs are continuously added to the queue
  • Does not take into account job priority or urgency
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25
Q

what is the shortest remaining time algorithm

A
  • The queue storing jobs to be processed is ordered according to the time left for completion, with the jobs with the least time to completion being serviced first
26
Q

what are the advantages of the shortest remaining time algorithm

A
  • Throughput is increased as shorter processes can be quickly completed
27
Q

what are the disadvantages of the shortest remaining time algorithm

A
  • Does not take into account job priority or urgency
  • Processor starvation if short jobs are continuously added to the queue
28
Q

What are the types of operating system

A
  • Distributed
  • Embedded
  • Multi tasking
  • Multi User
  • Real Time
29
Q

What is the distributed type of operating system

A
  • Run across multiple devices
  • Means the load of a task is spread across multiple computer processors
30
Q

What is the embedded type of operating system

A
  • Built to perform a small range of specific tasks
  • Catered towards a specific device eg. a household appliance.
  • Limited functionality and hard to update
  • Consume less power than other types of OS.
31
Q

What is the multi tasking type of operating system

A
  • Enables user to carry out tasks simultaneously.
  • Time slicing is used to switch quickly between programs and applications in memory.
32
Q

What is the multi user type of operating system

A
  • Multiple users make use of one computer.
  • A scheduling algorithm Is used to allocate processor time fairly between jobs and prevent processor starvation.
33
Q

What is the real time type of operating system

A
  • Used in time-critical computer systems and designed to perform a task within a guaranteed time frame.
34
Q

What is BIOS

A

● Basic Input Output System is the first program that runs when a computer system is switched on.
● Runs a series of tests before the operating system is loaded into memory:
● POST (Power-on self test) which ensures that all hardware is correctly connected and functional
● Checking the CPU clock, memory and processor
● Testing for external memory devices

35
Q

What are device drivers

A

● Computer programs that allow the operating system to interact with hardware.
● Are specific to the computer’s architecture.
● Specific to the operating system .

36
Q

What are virtual machines

A

● A theoretical computer and a software implementation of a computer system.
● Provides an environment with a translator for intermediate code to run.

37
Q

What are the uses of intermediate code

A

● Testing programs
● Protection from malware
● Running software compatible with different versions/ types of operating systems

38
Q

What is intermediate code

A

● Code halfway between machine code and object code is called intermediate code.
● Independent of processor architecture so can run across different machines and operating systems.
● Takes longer to execute than low-level code

39
Q

What is application software

A

● Used by the end-user
● Perform one specific task

  • Examples: desktop publishing, word processing, spreadsheets, web browsers.
40
Q

What is system software

A

● Manages computer resources
● Ensures consistently high performance.

  • Examples: library programs, utility programs, operating system, device drivers
41
Q

What are utilies

A

● Maintain a high-performing operating system.
● Each utility has a specific function

  • Examples: compression, disk defragmentation, automatic updating, automatic backup
42
Q

hat is source code

A
  • Code written by a programmer
43
Q

What is open source code

A

● Can be used without a license
● Distributed with the source code.

44
Q

What are the advantages of open source code

A
  • Improved by community effort.
  • Technical support from online community.
  • Can be modified and sold on for profit.
45
Q

What are the disadvantages of open source code

A
  • Inadequete support available (no user manuals)
  • Lower security
46
Q

What is closed source code

A
  • User must hold correct license
  • Users cannot access source code
  • Company owns the copyright license
47
Q

What are the advantages of closed source code

A
  • Regular well tested updates
  • Company provides expert support and user manuals
  • Highly levels of security as developed professionally
48
Q

What are the disadvantages of closed source code

A
  • License has restrictions about use
  • Users can not modify and improve code
49
Q

What is a translator

A

● A program that converts source code into object code. There are three types:

  • Compiler
  • Interpreter
  • Assembler
50
Q

What is a complier translator

A

● Translate high-level code into machine code all at once.
● Initial compilation process is longer than using other translators.
● Compiled code is platform-specific
● Compiled code can be run without a translator present.

51
Q

What is a interpreter translator

A

● Translate and execute code line-by-line.
● Produce an error if a line contains an error.
● Slower than running compiled code.
● Correct interpreter required to run on different platforms.
● Code is platform-independent.
● Useful for testing code.

52
Q

What is an assembler interpreter

A

● Assembly code is a low-level language that is platform specific.
● Assemblers translate assembly code into machine code.
● Each line of assembly code is equivalent to almost one line of machine code.

53
Q

What are the stages of compilation

A
  • Lexical analysis
  • Syntax analysis
  • Code Generation
  • Optimization
54
Q

What is lexical analysis

A

● Whitespace and comments are removed.
● Keywords and identifiers are replaced with tokens.
● Information about tokens is stored in a symbol table

55
Q

What is syntax analysis

A

● Tokens analysed against rules of the programming language.
● Syntax errors are flagged up.
● Abstract syntax tree is produced

56
Q

What is code generation

A

● Abstract syntax tree used to produce machine code.

57
Q

What is optimisation

A

● Aims reduce execution time
● Is a very time-consuming stage.
● Redundant parts of code are removed.

58
Q

What are linkers

A

● Software that links external modules and libraries included within the code.

59
Q

What is a static linker

A

● Module/library code is copied directly into the file.
● Increases the size of the file.

60
Q

What is a dynamic linker

A

● Addresses of modules/ libraries are added to the file.
● External module/library updates automatically feed through to the main file

61
Q

What are loaders

A

● Programs provided by the operating system.
● Fetches the library/ module from the given memory location.

62
Q

What is the use of libraries

A

● Pre-compiled programs which can be incorporated within other programs.
● Error-free
● Save time and effort of developing and testing modules.
● Can be reused across multiple programs
● Save programmers from ‘reinventing the wheel’

Computer Science (8 decks)

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