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GCSE - Computer Science > Unit 1 - System Architecture✔️ > Flashcards

Unit 1 - System Architecture✔️ Flashcards

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1
Q

Three example of input devices?

A

Keyboard,scanner,microphone

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2
Q

Three example of output devices?

A

Speakers,display or printer

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3
Q

What is the cpu?

A

Central processing unit - process input,store data and output results it is the brains of the computer and executes instructions

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4
Q

How did early computers store data to be worked on?

A

Before 1943 early computers stored data to be worked on in memory - the program was not stored - instructions were input one at a time usings switches and executed one at a time

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5
Q

Who is von Neumann and what did he do?

A

• In 1943-44, mathematician von Neumann had the idea of storing the program instructions as well as the data in memory

• The stored-program computer was born

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6
Q

How does Von Neumann architecture work?

A

Program instructions and the data the programs are using are both stored in the same memory - the CPU accesses both instructions and data from the same RAM

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7
Q

Main components of the CPU?

A

• Control Unit
• Arithmetic-Logic Unit (ALU)
• registers
• Cache

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8
Q

What is the CPU’s register?

A

• A register is a very fast memory location in the CPU itself

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9
Q

What is a cache?

A

• Cache is located on the CPU – it is slower to access than registers but faster than RAM

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10
Q

What are the main registers in the CPU?

A

•Program Counter (PC)

• Memory Address Register (MAR)

• Memory Data Register (MDR)

• Accumulator

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11
Q

What does the program counter do?

A

holds the address of the next instruction to be executed

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12
Q

What does the memory address register do - MAR?

A

holds the memory address of the current instruction to be executed, and then the data that it uses, so that these can be fetched from memory

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13
Q

What does the memory data register do - MDR?

A

holds the actual instruction, and then the data that has been fetched from memory

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14
Q

What does the acccumulator do?

A

holds the result of an instruction before it is transferred to memory

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15
Q

What does the control unit do?

A

• The control unit coordinates and controls all of the activities taking place within the CPU

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16
Q

List three things the control unit does?

A

• It decodes instructions and executes them
• It receives signals from the system clock
• It directs the timing and control of other parts of the CPU

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17
Q

What is the purpose of the arithmetic logic unit - ALU?

A

The ALU or Arithmetic Logic Unit is where the actual arithmetic operations are done - It also carries out logical operations such as those including AND, OR and NOT

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18
Q

What is the fetch - decode - execute cycle?

A

Three operations operated by the cpu:
• FETCH – causes the next instruction and any data involved to be fetched from main memory
• DECODE – decodes the instruction
• EXECUTE – the instruction is executed

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19
Q

What does the program counter do?

A

• The Program Counter holds the address of the next instruction to be executed - increased by 1 as soon as the instruction has been fetched

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20
Q

What is the purpose of the accululator - ACC?

A

The accumulator (ACC) is where arithmetic and logic results are temporarily stored

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21
Q

Explain in depth what happens during the fetch stage of Fetch,decode,execute cycle?

A

1) the memory Addresss held in the program counter is copied into the MAR

2) the address in the program counter (PC) is then increased by 1 - the PC now holds the address of the next instruction to be fetched

3)processor sends a signal along the address bus to the memory address held in the MAR

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22
Q

How does the MAR and MDR work together?

A

The two work together; The MAR knows where to look for data in RAM, the MDR keeps hold of that data until it’s ready to be used by the CPU

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23
Q

Three factors that affect CPU performance?

A

• Clock speed
• Processor cores
• Cache

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24
Q

What is clock speed?

A

Cycles per second measured in hertz (Hz) - faster clock speed - faster the instructions are processed

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25
Q

What is a CPU’S number of cores?

A

The number of duplicate processing units (cores) placed in one CPU

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26
Q

What is a CPU’S cache size?

A

Memory on the CPU that is faster than RAM but slower than registers and is expensive

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27
Q

Units and values of clock speed?

A

1 cycle per second eg 1 instruction carried out = 1Hz

• 1 kilohertz (kHz) = 1000 cycles per second
• 1 Megahertz (MHz) = 1,000,000 cycles per
second
• 1 Gigahertz (GHz) = 1,000,000,000 cycles per second

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28
Q

what is clock speed?

A

1 cycle per second eg 1 instruction carried out = 1Hz

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29
Q

What are the benefits of dual core cpu?

A

• A dual-core processor has the potential to perform two instructions at the same

• This allows twice as many instructions to be executed - not always taken advantage of by software

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30
Q

What is the cpus cache?

A

• Cache is a small amount of very fast, expensive memory in the CPU

• It can be accessed faster than regular main memory (RAM)

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31
Q

What is an embedded sysetm?

A

A computer system that is used to control mechanical or electrical systems - includes RAM,ROM and a cpu

32
Q

Name three examples of an embedded system?

A

-microwave
-dishwasher
-satnav

33
Q

CPU speed of embedded systems?

A

Typically slow

34
Q

CPU speed of genreal purpose machines?

A

Typically very fast

35
Q

Software of embedded systems?

A

Has one purpose and cannot install new software

36
Q

Software of genreal purpose machines?

A

New software can be installed

37
Q

Storage of genreal purpose machines?

A

Programs stored on hard drives

38
Q

Software of embedded sysetms?

A

Programs stored on ROM

39
Q

Reliability of genreal purpose machines?

A

Runs many programs and may be less reliable and need restarting

40
Q

Reliability of embedded systems?

A

Typically very reliable

41
Q

Why is primary storage needed for Von Neumanns architecture?

A

primary storage is needed to store programs that are currently running and need to be accessed by the CPU

42
Q

What is RAM?

A

Random Access memory - is primary storage that is much faster than a hard drive and stores the operating system and other important operations

43
Q

List three things RAM stores?

A

-the operating system
-software currently in use
-the data which the software is using

44
Q

Is Ram volatile?

A

Yes - looses data is the power is off

45
Q

Example of non-volatile storage?

A

Hard drive - programs and data are permantley stored here and are not lost if the power is off

46
Q

What is virtual memory?

A

• Virtual memory is part of the hard drive used as an extension to RAM

47
Q

Advantages of virtual memory?

A

• Uses cheap secondary storage on the hard drive
• Prevents error messages saying ‘out of memory’ – the programs and files will still open

48
Q

Disadvantages of virtual memory?

A

• Accessing virtual memory is very slow
• To access data, the existing data in RAM needs to be copied to the virtual memory, then data in virtual memory needs to be copied to RAM

49
Q

What is ROM?

A

Read only memory - primary storage that does not loose data when the power is off and stores the initial program that is run when the computer is turned on

50
Q

Two things ROM stores?

A

-boostrap - inital program which tells the operating sysetm where to find the operating system in the hard drive

-BIOS - stores basic configuration of pc like processor speed

51
Q

Does RAM an ROM both have a read and write ablility?

A

No - RAM does but ROM can not write only read

52
Q

What is secondary storage?

A

• Secondary storage is not directly accessible by the CPU
• It is non-volatile, meaning it will keep data even if there is no power
•can be external or internal

53
Q

Three uses of secondary storage?

A

-programs and data stores on hard drive
-SD cards can be used for additional storage on cameras and phones
-memory sticks to transport data from one place to another

54
Q

2 examples of secondary storage?

A

-HDD - hard drive
-SSD - solid state drive

55
Q

2 examples of offline secondary storage?

A

-falsh memory eg SD cards
-removable HDD or SSD

56
Q

List three storage methods?

A

• Magnetic
• Optical
• Solid State

57
Q

How does a magnetic storage device work?

A

• Magnetic: Mechanical parts move over the disks surface to read and write data magnetically, or a drive head reads a magnetic tape

58
Q

How does a optical storage device work?

A

• Optical: Lasers read and write data using lig

59
Q

How does a solid state storage device work?

A

• Solid State: Data is recorded onto solid memory chips without any moving parts

60
Q

Describe the features of magnetic disks?

A

Disk contains circles called tracks which are each divided into sectors - with disk heads mounted on mechanical arms which read and write data

61
Q

What moves the read/write arm?

A

Actuator moves the read/write arm

62
Q

Advantages of magnetic storage?

A

-Cheap
-large storage capacities
-relativley fast write speed

63
Q

Disadvantaged of magnetic storage?

A

-lots of mechanical parts - can make them less durable

64
Q

Explain how optical storage works?

A

-data stored as pits and lands pressed into a spiral track circulating outwards from the centre
-laser beam passes over the pits and lands - level of reflection is measured
-from the signal, 0s and 1s can be derived

65
Q

Advantages of optical storage?

A

-cheap
-very easily portable
-take up little space physically

66
Q

Disadvantages of optical storage?

A

• Less storage capacity compared to other types
• Easily damaged / scratched, requires a CD reader
• Slow write s

67
Q

Why can blu-ray disks store more then CD disks despite the same physical size?

A

CD has bigger pits and lands (as red light has a large wavelength) so the smaller blu-ray pits and lands allow it to store more data

68
Q

What are the basic features of SSD?

A

•Solid-state disks use non-volatile flash memory to store information
• Very fast read/write speeds as it doesn’t need to wait for a disk to spin to the correct location and an arm to move
• No mechanical or moving parts meaning these disks are very durable

69
Q

Explain how flash memory works?

A

• Large electric current used to force electrons through a barrier and trap them on the other side
• They remain on the other side until ‘flashed’ with a new current, hence the name

70
Q

Advantages of SSDs?

A

• Highly durable, no moving parts, very fast read/write speeds, no noisy fan or drive arm, faster start up times

71
Q

Disadvantages of SSDs?

A

• More expensive than magnetic hard disks, similar storage capacity as magnetic disks

72
Q

Explain in depth what happens during the decode stage of Fetch,decode,execute cycle?

A

4) the instruction/data held in that memory address is sent along the data bus to the memory data register (MDR)

5) the instruction/data held in the MDR is copied to the current instruction register (CIR)

73
Q

Explain in depth what happens during the execute stage of Fetch,decode,execute cycle?

A

6) the insturction/data held in the current instruction register (CIR) is decoded and the executed in the control unit (Cu) - results are stored in the accumulator (AAC)

7)cycle returns to step one

74
Q

What is the current instruction register (CIR)?

A

Holds the instruction that is currently being decoded and executed

75
Q

What registes are involved in the fetch phase in the cpu?

A
  • PC - program counter
  • CIR - current instruction
  • MAR - memory address register
  • MDR - memory data register

GCSE - Computer Science (10 decks)

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