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OCR AS Computer Science > Unit 1 (Computer systems) > Flashcards

Unit 1 (Computer systems) Flashcards

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1
Q

Explain one benefit of using paging for memory management on a laptop. (2)

A
  • Programs/data can be held in non-contiguous memory locations (using virtual addressing)…
  • …making it easier to make best use of remaining storage/ to avoid having to move content around to fit in new programs.
  • It allows pages to be transferred to and from secondary storage (i.e. virtual memory).
  • As random access there is no performance drop vs sequential storage.
    (1 per -, max 2)
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2
Q

At what stage would an interrupt be handled in the FDE cycle. (1)

A

The execute stage

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3
Q

State the type of translator that is used to convert assembly language into machine readable code. (1)

A

Assembler

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4
Q

State why computer systems store data in binary. (1)

A
  • Computers use binary logic for on/off or 1/0
  • Computer systems are based on switches/transistors
  • Binary is high tolerance
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5
Q

Describe the purpose of the Regulation of Investigatory Powers Act. (3)

A
  • Sets out to empower/ limit the extent to which public bodies can use technological surveillance.
  • This can include monitoring internet activity.
  • Electronic communications.
  • And forcing users to hand over encryption keys.
    (1 per - , max 3)
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6
Q

Show the denary number −2⅝ as a floating-point binary number with a 6-bit mantissa and
4-bit exponent, both stored using two’s complement representation.

A

101011 0010

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7
Q

State the name of one scheduling algorithm other than First Come First Served. (1)

A
  • Round Robin
  • Multi-level feedback queues
  • Shortest job first
  • Shortest time remaining
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8
Q

State what is meant by the term real-time operating system. (1)

A

The system gives a response within a guaranteed time frame. (1)

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9
Q

Describe why ‘Film Title’ is not a suitable primary key. (2)

A

A primary key must have a unique value for each record (1) – however it is possible for two films to have the same name (1).

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10
Q

Convert the denary number 171 into a hexadecimal number. (1)

A

AB

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11
Q

(unsigned)

11011011
10001001 +

A

0110 0100

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12
Q

State which method of compression is most likely to be used for photographs on webpages. (1)

A

Lossy

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13
Q

State two functions of an operating system other than memory management and scheduling. (2)

A
  • Peripheral management
  • Handle interrupts
  • File management
  • Provides a user interface
  • Provides platform to install and run software.
  • Provides utilities for system maintenance.
  • Allows multi-tasking
  • Provides security
    (1 per -, max 2)
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14
Q

Convert the denary number 43 into an 8 bit binary number. (1)

A

00101011

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15
Q

What type of network model is used when a user can stream a movie of another users computer rather than the company’s servers. (1)

A

Peer to peer (1).

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16
Q

Convert the two’s complement binary number 10011011 into a denary number. (1)

A

-101

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17
Q

Using two’s complement convert the denary number -43 into an 8 bit binary number.

A

11010101

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18
Q

Explain why all closed source software is most likely to be compiled rather than run on an interpreter. (2)

A
  • Compilers translate the source code prior to distribution.
  • Meaning the user gets an executable program (which makes amending of the program much more difficult).
  • Interpreters translate source code every time the program is run meaning the user needs the source code to run the program.
    (1 per - , max 2)
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19
Q

Describe what is meant by the term ‘BIOS’. (2)

A
  • Stored in ROM
  • Tests hardware/components (are working)
  • Boots up the operating system
    (1 per -, max 2)
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20
Q

Convert the binary number 10110011 into a hexadecimal number. (1)

A

B3

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21
Q

Convert the denary number –17 into an 8-bit binary number using sign and magnitude. (1)

A

1001 0001

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22
Q

Define the term ‘array’. (2)

A
  • A data structure/holds multiple pieces of data
  • Has a single identifier
  • Elements are accessed by an index
  • Holds data of the same data type
  • Elements are stored contiguously in computer memory
    (1 per - , max 2)
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23
Q

Describe one difference between paging and segmentation. (2)

A
  • Paging uses physical addressing….
  • ….Segmentation uses logical addressing
  • Paging uses fixed size memory blocks….
  • …. Segmentation uses variable length memory blocks
    (1 per -, max 2)
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24
Q

Explain why the Harvard architecture is suitable for a washing machine. (2)

A
  • Fixed instruction size
  • No need for memory to be shared between data and instructions
  • Removes need for secondary storage
  • Instructions would never be changed
    (1 per -, max 2)
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25
Q

Using normalised floating point binary representation using 4 bits for the mantissa and
4 for the exponent, represent the denary value -1.75.

A

1001 0001

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26
Q

Describe how you can use iteration when reading from a text file. (2)

A
  • To setup a loop…
  • To repeat (the same block of code)
  • for each line in the text file // until each value has been read.
    (1 per -, max 2)
27
Q

Describe one difference between CISC and RISC (2)

A
  • Some instructions in CISC will rarely get used …
  • … In RISC instructions are used regularly
  • In assembly for CISC, a statement that takes one mnemonic …
  • … (may) take multiple mnemonics in RISC
  • Compilers for RISC need to be more complex …
  • … than compilers for CISC
  • CISC architecture has complex circuitry and is therefore more expensive to manufacture…
  • …RISC architecture has simple circuitry minimising manufacture cost.
    (1 per -, max 2)
28
Q

Describe what is meant by the term JavaScript. (2)

A

A programming language that runs in a web browser (1) that can be embedded into HTML (1) with script tag (1) to add interactivity to a page (1).

29
Q

Using normalised floating point binary representation using 4 bits for the mantissa and
4 for the exponent, represent the denary value 1.75.

A

0111 0001

30
Q

State if removing an external hard disk drive from a computer would need to interrupt the current fetch-decode execute cycle of the CPU. (1)

A
  • GUI will need to remove open file manager windows
  • OS will need to remove open files/release locks
  • Inform the CPU to cease transferring files
31
Q

Describe what happens to the contents of RAM and ROM when power to the system is removed. (2)

A

The contents of RAM are wiped (1) whereas the contents of ROM remain the same (1).

32
Q

Explain why it is usually the case that JavaScript is interpreted rather than compiled. (2)

A

JavaScript is likely to be run on a variety of machines (1) with different processors/architectures (1). Compiled code is machine dependent (1) whereas interpreters run on high level code (1) which is machine independent (1).

33
Q

Explain how the Domain Name System (DNS) plays a role in websites being loaded. (2)

A
  • DNS is used to resolve IP corresponding to URL
  • Request sent to DNS resolver.
  • Resolver checks its cache and if it doesn’t hold the URL, it passes it in to the TLD Name server which checks its cache and returns the answer or passes on to the..
  • Authoritative Name Server.
  • The IP address is returned back up to the requesting client.
  • Or an error if no resolution can be found.
    (1 per -, max 2)
34
Q

Give three functions of an operating system. (3)

A
  • Provide a user interface
  • Provide System Security
  • Manage hardware
  • Provide utilities
  • Provide a platform from which software can be installed/run
  • Schedule jobs
  • Handle interrupts
  • Manage memory
    (1 per - , max 3)
35
Q

Describe how a stack is used when handling interrupts. (2)

A
  • Stacks use LIFO/FILO storage
  • As processes are halted by an ISR they are pushed on the stack
  • When they are returned, they are popped from the top of the stack
  • So they are returned to in correct order
    (1 per -, max 2)
36
Q

Describe what is meant by the term ‘Von Neumann Architecture’. (1)

A
  • Uses the same memory for data and instructions
  • Uses the same bus for data and instructions
  • Can only fetch either data or instructions at one time/follows FDE
    (1 per -, max 3)
37
Q

Describe the Harvard architecture. (2)

A
  • Uses separate memory blocks for instructions and data
  • Has separate buses (data and address) for data and instructions
  • Has fixed memory sizes for data and Instructions
  • Instruction memory may be ROM
    (1 per -, max 2)
38
Q

00011010
00110010 -

A

00011000

39
Q

Name the register in which the result of arithmetic operations are stored. (1)

A

The accumulator (1).

40
Q

Give an example of why a website might use CSS. (1)

A
  • To define the formatting of a website.
  • To change the formatting depending on device.
  • To give a consistent look to every page.
  • To set the formatting {sensible example of part of site}.
    (1 per -, max 1)
41
Q

Explain two reasons why you would use flash technology to store files over a magnetic hard drive. (4)

A
  • Faster read/write times
  • More portable/durable.
  • Lower power consumption
  • Quieter running
42
Q

Explain one advantage of using layers in the protocol TCP/IP. (2)

A
  • Allows different layers to be worked on independently
  • Allows layers to be replaced/upgraded without affecting others
  • Allows for layers from different providers to be used interchangeably
    (1 per -, max 2)
43
Q

State what is meant by the term ‘protocol’. (1)

A

A set of rules (for communication).

44
Q

Explain why a company may opt for a peer to peer model. (2)

A

Peer to peer means there isn’t a reliance on the company’s server (1) and its connection to the Internet (1).
This means it hasn’t got to invest in lots of hardware and bandwidth (1) and the system is likely to be more fault tolerant (1).

45
Q

Convert the denary number –97 into an 8-bit binary number using two’s complement. (1)

A

1001 1111

46
Q

Explain why First Come First Served is a suitable scheduling algorithm for a router. (2)

A
  • Jobs dispatched on a FIFO basis
  • Each job/packet is equal priority
  • Each job/packet switch has the same processing time
    (1 per -, max 2)
47
Q

State what opcode SUB does. (1)

A

Performs subtraction (1).

48
Q

State which of a stack or queue would be considered as a ‘First In First Out’ data structure. (1)

A

A queue

49
Q

Describe why ‘Film Title’ would make a suitable secondary key. (2)

A

A secondary key is indexed allowing for faster searching (1) and users are likely to want to search by film (1).

50
Q

State the name of one utility that you could install on a laptop. (1)

A
  • Disk Defragmentation
  • System Clean-up
  • Anti-Virus/Malware
  • Firewall
  • File management
  • Disk Drivers
51
Q

Convert the binary number 11101100 into a denary number. (1)

A

236

52
Q

Convert the denary number 97 into an 8-bit binary number. (1)

A

0110 0001

53
Q

Describe what happens during the ‘Fetch’ stage of the FDE cycle. You should refer to the use of specific registers in your answer. (4)

A
  • Data/address is copied from PC to MAR
  • PC is incremented (by 1) (this can be in any location from here down)
  • Data in MAR is passed onto the Address Bus
  • Read signal is sent onto the control bus
  • RAM copies the data from the location specified by the address bus onto the data bus
  • Data on the data bus is passed into the MDR
  • Data is copied from the MDR to the CIR
    (1 per -, max 4)
54
Q

Explain the difference between open source and closed source software. (4)

A
  • Open source has the source code freely available to amend/copy/redistribute/recompile.
  • Whereas closed source is distributed in binary form only/the source code is not made available.
  • There are licensing conditions restricting the redistribution/there is no permission to amend the (program) code.
    (1 per - , max 4)
55
Q

Explain why photographs on webpages must be compressed. (2)

A
  • Reduces the size of the image file
  • Uses lower bandwidth in transmission
  • Takes up less storage (on the HTTP server)
    (1 per -, max 2)
56
Q

Explain why a real-time operating system would be suitable for this purpose of monitoring a patients vital signs. (2)

A

If something happens to a patient, a response must be immediate (1).
Other types of system may have delays in response (1).
This could result in a patient not receiving treatment in time (1).

57
Q

Explain two advantages of a vital sign monitoring system having its operating system stored in ROM. (2)

A

ROM is quick to start up so the system can be started up quickly (in an emergency) (1).
ROM cannot be altered so there is no chance of the OS being accidentally or maliciously changed (on what is a safety critical system) (1).

58
Q

Show the denary number 35 as an 8-bit (unsigned) binary number.

A

00100011

59
Q

State one advantage of using two’s complement instead of sign and magnitude. (1)

A
  • Can be easily used in binary arithmetic
  • Increased range of numbers available
60
Q

11010011
01111001 –

A

01011010

61
Q

State the name of a type of translator software other than a compiler or interpreter. (1)

A

An Assembler

62
Q

Explain two other pieces of utility software that you should install on a computer. (4)

A
  • Disk Defragmentation…
  • …To keep optimal r/w speed for her HDD
  • File management…
  • …To allow easy access to her file system
  • Disk Drivers…
  • … To allow her to use new peripheral devices
  • System Clean-up…
  • … to keep her system free of redundant files
  • Anti-Virus/Malware…
  • … to find and remove/quarantine viruses/malware (A worms/trojans etc)
    (1 per -, max 4)
63
Q

State in order the 4 layers of the TCP/IP stack. (4)

A
  • Application
  • Transport
  • Network
  • Link

OCR AS Computer Science (2 decks)

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