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computer science ongoing flashcards > Set 5 > Flashcards

Set 5 Flashcards

1
Q

What is application software? Give 3 examples

A

Application software is designed to perform tasks a user wants to complete (user-oriented tasks), e.g. word processors, spreadsheet software, movie editing etc.

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2
Q

What is systems software?

A

Systems software is software used in the management of a computer system.

This comprises layers of software that abstract the user from how the computer works.

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3
Q

What are utility programs?

A

Utility programs are systems software that is used to perform a non-core/ancillary/specific management function for a computer.

They help to manage or maintain a computer system but are not critical to the system.

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4
Q

What are two ways utility programs can be installed

A

Utility programs can either be supplied with the operating system or installed at a later time.

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5
Q

Give four types of system software

A

Operating System
Utility Programs
Libraries
Translators

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6
Q

Give three examples of utility programs

A

antivirus software, defragmentation, compression

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7
Q

What are libraries?

A
  • Libraries are precompiled, pretested routines (sets of code) that other programs can link to and use
  • As long as the programmer includes a reference to the library in their code, they can access all the functions of the library
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8
Q

How do libraries save developers time?

A
  • Common tasks can be written as libraries for repeated use
  • This saves time for developers as it saves them from having to rewrite the instructions
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9
Q

What are translators?

A

Translators are systems software tools that are used to convert program code from one format into another, without adjusting the logical operation of the original program code

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10
Q

Name three types of translator

A

Compilers, Assemblers, Interpreters

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11
Q

What is the purpose of compilers?

A

To turn program source code into a target language version (eg machine code / bytecode) that can be executed by the computer

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12
Q

What is the purpose of assemblers?

A
  • To turn low-level assembly language code into executable machine code
  • They are very fast to run
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13
Q

How do interpreters work?

A

Interpreters run instructions from a high-level language by determining what actions should occur line-by-line and executing equivalent prewritten executable code.

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14
Q

Why is the operating system classified as systems software?

A

It is required for the functioning/maintenance of the system itself, and performs tasks that are machine oriented

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15
Q

2 main roles of OS

A
  1. To hide the complexities of the hardware from the user
  2. To manage the resources which processes compete for

Give a concrete example, e.g. “To allocate I/O devices to processes”

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16
Q

How does the OS hide the complexities of the hardware from the user?

A

By presenting the user with a virtual machine to interact with.
e.g.
- Graphical User Interfaces (GUIs)
- Command Line Interfaces (CLIs)
- Application Programing Interfaces (APIs)

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17
Q

What is a virtual machine?

A

A virtual machine is the apparent machine or interface that the OS presents to the user

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18
Q

What is a process?

A

A process is an instance of a program being executed

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19
Q

Give four resources processes compete for:

A
  • (Secondary) Storage
  • I/O Devices
  • Memory
  • Processor time
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20
Q

Give four ways the OS manages storage:

A
  • Allocating space on storage devices to files
  • Organising files into directories
  • Determining where on the device to save a file
  • Manages which process/user can access (read/write/modify) different files and directories
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21
Q

How does OS manage I/O devices?

A
  • By allocating I/O devices to different processes
  • And managing communication between the processes and devices
22
Q

How does OS manage memory?

A

By allocating different parts of main memory for all the processes. (Locations may not be contiguous)

23
Q

How does OS manage processors?

A

By allocating processor time to each of the processes (aka processor scheduling)

24
Q

Give four characteristics of a low-level language:

A
  • They are defined by the processor they are designed to run on
  • Non portable - they are specific to the instruction set of the processor they are written for
  • They are machine-oriented and have no built-in functions
  • There is a one-to-one mapping between a low-level language instruction and its equivalent machine code language instruction
25
Q

Why are low-level languages non-portable?

A

They are specific to the instruction set of the processor they are written for

26
Q

What two things make up a low level instruction?

A
  • Opcode - an mnemonic which represents the machine operation that the processor should perform
  • Operand(s) - a value or set of values relevant to the opcode
27
Q

Give three things the operand of a low level instruction can be, and what addressing type it is

A
  • memory locations (direct memory addressing)
  • register values (direct register addressing)
  • actual decimal values (the operand is the datum) (immediate addressing)
28
Q

Why is hexadecimal used in some low level languages?

A
  • Binary machine code is difficult for humans to debug and fix problems in.
  • So hexadecimal is usually used instead, as it is easier to read and understand
29
Q

What is assembly code?

A
  • A low-level language that uses a set of mnemonics that represent binary machine code instructions
  • Assembly code is converted into machine code using an assembler.
30
Q

Give three characteristics of high-level languages

A
  • High-level languages are problem oriented
  • Portable - not specific to any type of processor
  • One instruction in a high-level language represents many instructions in a low level language
31
Q

What is an imperative language?

A
  • A high level language where a problem is solved by writing a sequence of instructions that state how it should be solved
  • It has structures for assignment/iteration/selection and uses English-like keywords for these
32
Q

Give four pros of high-level languages:

A
  1. Programs are machine independent / portable
  2. People find it easier to debug high-level language programs
  3. People find it easier to read/write/understand high-level language program code
  4. Saves time for programmers as they use fewer lines of program code
33
Q

Give four cons of high-level languages:

A
  1. Programs written in a high-level language may not make best use of specific features of a particular processor
  2. Programs written in a high-level language may not execute as quickly
  3. Programs written in a high-level language may use more memory
  4. Some programs are easier to write using a low-level language - e.g. some parts of a computer’s operating system
34
Q

Give four pros of low-level languages:

A
  1. Programs written in a high-level language may not make best use of specific features of a particular processor
  2. Programs written in a low-level language may execute quicker
  3. Programs written in a low-level language may use less memory
  4. Some programs are easier to write using a low-level language - e.g. some parts of a computer’s operating system
35
Q

Give four cons of low-level languages:

A
  1. Non-portable as they are specific to the instruction set of the processor they are written for
  2. People find it harder to debug low-level language programs
  3. People find it harder to read/write/understand low-level language program code
  4. Requires programmers to write more lines of program code
36
Q

What is a low-level language?

A
  • A language that is based upon the instruction set of a processor
  • They are defined by the processor they are designed to run on
37
Q

What is immediate addressing?

A
  • When the operand value is an actual decimal value that is part of the instruction
  • There is no need to go to any memory address in this case
38
Q

Give three advantages of compilers (over interpreters):

A
  • The source code cannot be accessed by users
  • Users do not need to have an interpreter to the run the program
  • The program will execute more quickly
39
Q

Why is code that will be executed in a web browser often interpreted rather than compiled?

A
  • It’s impossible to know what type of processor will be in the user’s computer
  • A compiled program will only execute on a processor of a specific instruction set, whereas interpreters can execute on a computer with any type of processor
40
Q

Why are translators necessary?

A
  • High-level instructions cannot be executed directly
  • Processors can only execute machine code instructions
41
Q

How do compilers and interpreters approach errors differently?

A
  • Compilers analyse the program as a whole, and will not translate any of the program if it encounters an error
  • Interpreters analyse the program on a line-by-line basis, and execute until the first error is encountered
42
Q

Give an example of an intermediate language and how its used

A
  • Bytecode
  • Compilers convert high-level code into bytecode, and then use a virtual machine to execute the bytecode on different processors
43
Q

What is the difference between source code and object code?

A
  • Source code is the input to a translator
  • Object code is the output of a translator
44
Q

Explain the relationship between hardware and software

A
  • Software is the programs that execute on the hardware
  • Hardware is the physical components that allow the software to execute
45
Q

What does computationally secure mean for a cipher?

A

A cipher is computationally secure if it cannot be cracked in ‘reasonable time’.

46
Q

What are the disadvantages of Caesar cipher?

A
  • Easy to crack because there are only 25 keys
    • → so very quick to crack with brute force
  • Frequency analysis reveals the likely shift
  • Word structure is preserved
  • Key length is such shorter than the message
  • So NOT computationally secure
47
Q

What is encryption?

A

The process of converting plaintext to ciphertext, so that it cannot be understood if intercepted

48
Q

What is special about a Vernam cipher key?

A
  • The key is randomly generated, or taken from a ‘one-time pad’.
  • and key length = plaintext length
49
Q

What operation does the Vernam cipher use for encryption and decryption?

A

XOR

50
Q

What are the five conditions for perfect security?

A
  • Key is chosen truly randomly
  • Key is only used once
  • Key is known only to the sender and receiver
  • Key must be destroyed after use
  • Key length at least message length
51
Q

What is symmetric encryption?

A

When the same key is used for both encryption and decryption

computer science ongoing flashcards (11 decks)

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