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A Level OCR Computer Science > Section 2 Systems Software > Flashcards

Section 2 Systems Software Flashcards

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1
Q

Where is the operating system stored?

A

Permanent storage, e.g. hard disk

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2
Q

How is the operating system brought from secondary to primary storage?

A

A program called the loader (which is stored in ROM) copies the OS from storage to RAM

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3
Q

What 5 things does an os do aside from the UI?

A

Memory management
Interrupt service routines
Processor scheduling
Backing store management
Management of all input and output

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4
Q

How does paging work?

A

Memory is divided into 4Kb fixed pages. When data is stored in memory, a program may take up a number of consecutive addresses. A table is then made to map the physical memory address to the logical memory address.

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5
Q

What is segmentation?

A

Segmentation is the logical division of address space into varying segments (different sizes). As with paging, you can load a part of the program into memory initially.

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6
Q

Why does a full RAM cause a computer to slow down?

A

The computer has to swap pages in and out of RAM and secondary storage, it ends up doing this most of the time which tanks performance, this is known as thrashing.

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7
Q

What is meant by multi - tasking in a single core processor

A

When a processor with one core breaks down a large problem into small chunks and does those one after another to give the appearance of carrying out several tasks simultaneously.

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8
Q

What does the schedular do?

A

The schedular is a module in the operating system that makes sure processor time is used as efficiently as possible

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9
Q

What are the objectives of the schedular? (4)

A

Maximise throughput
Be fair to all users on a multi user system
Provide acceptable response time to all users
Ensure hardware resources are kept as busy as possible

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10
Q

What is backing store management?

A

The operating system keeps track of the locations in storage that are free so new files can be uploaded there. It also needs to know where files are stored so they can be quickly accessed

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11
Q

What does your computer do when talking to a peripheral (i.e. a printer) in order to not reduce performance?

A

It sends the data to be transferred to a buffer so that the CPU can continue on another task. This is to compensate for the difference in speeds between the CPU and the printer.

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12
Q

What is a distributed operating system?

A

A distributed operating system is a form of parallel processing where the operating system divides up tasks among multiple computers (often servers) to provide more power than a single large server

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13
Q

What two operating systems do mobile devices have?

A

Mobile operating system
Real-time operating system

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14
Q

What’s the purpose of the real time os in a smartphone?

A

It controls the low level hardware in a phone such as the radio or gps.

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15
Q

What are the main features of an os in a conventional household embedded system (4)

A

It will have a minimal user interface
It will accept input from sensors and output to control devices
Limited RAM so no complex memory management system
No permanent data storage devices to be managed

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16
Q

What will the features of the os in a real time system be? (I.e. airbus a320)

A

Must respond very quickly to inputs or sensors
Must be able to deal with many inputs simultaneously
Must have fail safe mechanisms if hardware fails
It must incorporate redundancy (if one part fails, switch to another)

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17
Q

Where is the bios stored?

A

EPROM (erasable programmable read-only memory)

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18
Q

What does the bios do?

A

It’s primary purpose is to initialise and test the system hardware components and then load the os

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19
Q

What does a driver do?

A

Provides a software interface for a particular hardware device like a printer

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20
Q

Why might an apple device install a different driver to a windows device for a printer?

A

Drivers are hardware specific and os specific

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21
Q

Def virtual machine

A

A virtual machine is any instance when software is used to take on the function of the machine often to emulate different hardware

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22
Q

What two categories of software are there?

A

Systems software, application software

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23
Q

What is system software?

A

The software needed to run the computers hardware including the os and utility programs

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24
Q

Give 2 main functions of an os

A

Resource management - managing computer hardware
Providing a UI

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25
Q

What are utility programs for?

A

They are pieces of software designed to optimise the performance of a computer or perform ‘housekeeping’ tasks.

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26
Q

What is a disk defragmenter and what does it do?

A

It reorganises a metal hard disk so that files which have been split up (fragmented) are recombined into a single series of sequential ‘blocks’ (sections of the hard disk)

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27
Q

What 4 things do backup services generally allow users to specify?

A

Where to store the backup
What to backup
How to run the backup (zip files or not)
When to run the backup

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28
Q

What does automatic update utility software do?

A

Makes sure that any software is up to date by searching the internet and installing the latest version if it is not currently installed

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29
Q

What 2 pieces of system software need automatic updating to work efficiently

A

Anti virus and firewall services need the latest protection to still work as intended.

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30
Q

Why is an automatic updater important for application software?

A

It means applications are kept as up to date as possible so bug fixes and improvements are automatic and seamless to the user.

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31
Q

What does a virus checker do?

A

Checks your hard drive and (depending on level of protection offered) your emails and installed data and removes them

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32
Q

Why might someone use compression software?

A

To be able to send a file with a size limit over the internet.

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33
Q

What are the 3 categories of application software?

A

General-purpose, special-purpose (which includes custom-written (bespoke) software and off the shelf software)

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34
Q

What is general purpose software?

A

Software such as a word processor or spreadsheet that is used for many different purposes

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35
Q

What is special purpose software.

A

Software that performs a single specific task or a set of tasks such as hotel booking systems or fingerprint scanners

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36
Q

What two ways a software be bought?

A

Off-the-shelf - ready to go straight after purchase but more general
Bespoke - custom written software maybe bought by a hotel to carry out a specific task

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37
Q

Features of off-the-shelf software

A

Cheaper than bespoke software
May contain unwanted features and not contains desired but not essential features
Ready to be installed immediately
Well documented, tested and error free

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38
Q

Features of bespoke software (compared to off-the-shelf software)

A

More costly to produce and purchase
Features customised to user requirements and other features added as needs arise
May take a long time to develop
May contain hidden errors

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39
Q

What 4 things does the Open Source Initiative say about open source software?

A

It is licensed to use but the license is free
Open source software must be distributed with the source code
Developers can sell the software they have created
Any software created from open source software must also be ‘open’

40
Q

What are 3 features of closed source software?

A

There are restrictions on how the software can be used
The original developer holds the copyright on the software
Users do not have access to the source code and can’t sell it on

41
Q

What is a benefit of proprietary software over open source?

A

Proprietary software (especially when developed by companies) usually comes with regular updates and technical support for users

42
Q

What 5 things might you consider when choosing software for a specific purpose?

A

Does it do everything you need it to?
Does it run on the available hardware?
Is it available off the shelf?
How much will it cost?
Is it well used, tried and tested?

43
Q

Why do different processors have different assembly code?

A

Assembly language is hardware specific

44
Q

How is assembly language converted to machine code?

A

The source code is converted to byte code (or straight to machine code) by a compiler to get the output machine code (or object code)

45
Q

How does a compiler work?

A

A compiler scans through source code performing different checks before converting to object code

46
Q

How does an interpreter work?

A

An interpreter reads source code line by line, analyses it, and if it contains no errors, translates and runs it.

47
Q

What do modern interpreted languages do to speed up run time?

A

The source code is scanned first and converted to byte code which is then executed by a byte code interpreter

48
Q

What is a big advantage of byte code?

A

You can achieve platform independence (programs can be run on any computer regardless of hardware capabilities.

49
Q

What is an advantage (not independence) provided by byte code?

A

It adds an extra layer of security between your computer and the software (if malicious)

50
Q

Advantages of a compiler (4)

A

The object code can be saved on disk
The object code executes faster than interpreted code
Object code can be distributed without the compiler
Object code is more secure as is much more difficult to ‘reverse engineer’

51
Q

Advantages of an interpreter (4)

A

Platform independence
It is useful for development as there is no need for lengthy compilation

52
Q

Disadvantages of an interpreter

A

The program may be slower than a compiled program since each statement has to be translated first

53
Q

What are the 5 steps in the compilation process?

A

Lexical analysis,
Parsing/syntax analysis,
Symbol table,
Semantic analysis,
Code generation and optimization

54
Q

What happens during lexical analysis? (3)

A

All whitespaces and comments are removed.
Simple error checks such as looking for illegal identifiers are carried out
Keywords, constants and identifiers are exchanged for tokens

55
Q

What is the symbol table during compilation?

A

The symbol table is a table built up by the lexer which keeps track of the run time memory addresses for each identifier, it holds things such as the type and kind of an item.

56
Q

What happens during syntax analysis?

A

The token stream for the lexical analysis is checked against the rules of the language by parsing.

57
Q

What happens during semantic analysis within compilation?

A

Semantic analysis checks the tokens for valid code (i.e. a variable that has been used but not defined.

58
Q

What happens during code generation in the compilation process?

A

The code is converted into machine/object code. This may take a few parses as code optimization takes place

59
Q

What happens during code optimization in compilation?

A

The compiler removes unused statements and variables. It also replaces inefficient code with code that achieves the same thing but in a different way.

60
Q

Define an operating system

A

A program or set of programs that manage the operations of the computer for the user. It is the bridge between the user and the computer hardware since users can’t directly control computer hardware

61
Q

Define a system interrupt

A

A signal from a program, hardware device or internal clock to the cpu to say when a program has been terminated or to request a service from the os.

62
Q

How do interrupts allow multi-tasking?

A

The system clock triggers an interrupt to allow the cpu to process something else

63
Q

What happens when the CPU receives an interrupt?

A

It suspends execution of the current program/process and disables interrupts of a lower priority. It then puts all the values of the program counter onto the stack and calls upon an interrupt service routine to deal with the interrupt.

64
Q

Name 5 different scheduling algorithms

A

Round robin
First come first served
Shortest remaining time
Shortest job first
Multi-level feedback queues

65
Q

Name 3 types of interrupts

A

Hardware
Software
Input/output

66
Q

Give 2 examples of a hardware interrupt

A

Power button pressed
Memory parity error (corrupt memory)

67
Q

Name 3 different software interrupts

A

Illegal instruction encountered
Arithmetic overflow
New log on request

68
Q

Give 2 examples of an input/output interrupt

A

Buffer nearly empty
Completed data transfer to/from a device

69
Q

What are the three levels to an os?

A

The bootloader, the kernel, the shell

70
Q

What happens when a process is blocked?

A

If a process is running and requires an input/output then it will be blocked while the CPU waits for the input/output response and it will carry on to execute the next process. When the response is received, the blocked process is returned to the back of the queue

71
Q

What is round robin scheduling?

A

In round robin scheduling, processes are added to a stack on a first in first out basis with each process getting a time slice or quantum of processor time defined by an interval timer set by the os to generate regular interrupts. If the process isn’t finished by then, the CPU moves on to the next process and the current process is returned to the stack.

72
Q

How does first come first served scheduling work?

A

The first job to arrive is the first one to be executed with no system of priorities

73
Q

How does shortest remaining time scheduling work?

A

The job with the shortest estimated time to complete is executed first, this reduces the queue length and the number of small jobs waiting behind big jobs

74
Q

How does shortest job first scheduling work

A

The program with the shortest estimated running time is run first.

75
Q

What is the main disadvantage with shortest time/job scheduling?

A

They require knowledge of how long a process is going to take which is fine for non time-sensitive tasks but otherwise can slow down a system or simply isn’t possible for a computer.

76
Q

How does multi level feedback queueing scheduling work?

A

Multi level feedback queues implements several job queues, allowing jobs to move between queues depending on their size and requirements. It attempts to keep I/O jobs as busy as possible possible so that I/O devices do not cause a bottleneck in the system. This helps maximise processor usage as it doesn’t have to wait for I/O devices

77
Q

What is a multi-tasking operating system?

A

An operating system, such as windows, that usually runs on a PC or laptop that can run many jobs simultaneously.

78
Q

What is a multi-user, multi-tasking system

A

A system that acts like a time-share where one single powerful mainframe or supercomputer is connected to dozens or hundreds of terminals where each terminal gets a slice of processor time according to a scheduling algorithm.

79
Q

Why might someone use a compressor or zip a file to make it smaller?

A

Sometimes applications limit the size of files that can be shared or stored. It also reduces broadband usage if the file is able to be transmitted.

80
Q

What is the difference between open-source software and freeware?

A

Freeware is free to use but the user does not gain access to the source code

81
Q

What is the name for the list of operations that a particular computer can execute (when talking about assembly language)

A

The instruction set

82
Q

What is the advantage of using a compiler to generate object code?

A

The object code can be distributed and executed without the compiler.

83
Q

How is a symbol table accessed to reduce the time the lexical analyser has to wait?

A

A hash table is used. Also synonyms (collisions) are inevitable and so are stored in the next available space

84
Q

What happens during parsing? (During syntax analysis)

A

Parsing is the task of systematically applying the rules of each statement to determine its validity. Stacks will be used to check if brackets are correctly paired.
The priorities of arithmetic operators are determined and converted to a form better for machine code.

85
Q

What is a disadvantage of code optimisation in compilation?

A

It can drastically increase compilation time it sometimes produces unexpected results.

86
Q

What is a linker and what does it do?

A

Once a program is compiled, the linker put the appropriate machine addresses in all the external call and return functions so that modules in the code are linked together correctly

87
Q

What does a loader do? (During compilation)

A

A relocating loader can load object code anywhere in memory provided it is in a relocatable format

88
Q

What are 2 advantages of using libraries in code?

A

They are tested and free of errors
They save the programmer time as they don’t have to ‘re-invent the wheel’

89
Q

Which types of operating systems are stored in read-only memory?

A

Real-time and embedded

90
Q

What is a linker?

A

A linker is a piece of software that links libraries to code that uses them

91
Q

What is a loader?

A

A piece of software that decides where the loaded machine code will go in memory

92
Q

What is a statically linked library?

A

A library that is included in the object code of a file.

93
Q

What is a dynamically linked library?

A

A library that is only loaded and given to the CPU when it is called

94
Q

What is one advantage and disadvantage of statically linked libraries?

A

The code that contains them takes up more space in memory
It takes less time to run because it is already in the object code

95
Q

What is one advantage and disadvantage of dynamically linked libraries?

A

The libraries are not included in the object code so it takes up less memory
The library needs to be installed on the end users device, this is time consuming and sometimes inconvenient

96
Q

Which types of operating systems are stored in RAM?

A

Embedded systems and real-time systems

A Level OCR Computer Science (12 decks)

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