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IGCSE Edexcel Computer Science > Hardware > Flashcards

Hardware Flashcards

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1
Q

What is meant by the term ‘computer architecture’?

A

The structure of a computer system - the hardware components it has and how they work together to execute programs

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2
Q

Give the core elements used in von Neumann architecture.

A
  • Input & output mechanisms
  • Main memory
  • Central processing unit (CPU)
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3
Q

John von Neumann proposed the concept of a stored program.

State the two items he proposed to store in main memory.

A
  • Program instructions
  • Data
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4
Q

Describe the function of the central processing unit.

A

To decode and execute program instructions fetched from memory

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5
Q

State what is meant by the term ‘program instruction’.

A

A task that is carried out by the CPU

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6
Q

(Exam-style question)

Von Neumann developed the stored program concept.

Describe the stored program concept. (2)

A
  • Instructions and data are stored in main memory
  • Instructions and data are fetched, decoded, and executed in a sequence by the CPU
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7
Q

(Exam-style question)

Describe how the CPU and main memory work together to run programs. (4)

A
  • Program instructions and data are stored in main memory and are fetched by the CPU one at a time, where they are decoded and executed
  • Results of operations carried out in the CPU are stored in memory
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8
Q

(Exam-style question)

Explain one reason why the stored program concept enabled computers to become general purpose machines capable of performing a variety of different tasks. (2)

A

Computers could be reprogrammed to carry out different tasks because they were able to store program instructions and data in memory

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9
Q

Give some examples of input devices and output devices.

A

Input -

  • Keyboard
  • Mouse
  • Scanner
  • QR code reader
  • Sensor
  • Microphone
  • Touchscreen / tablet

Output -

  • Monitor
  • Printer
  • Projector
  • Speaker
  • Touchscreen / tablet
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10
Q

Describe the characteristics of main memory.

A
  • It holds the program instructions and data that the CPU is currently using
  • It consists of a collection of storage locations, each with its own unique address

(a storage location can hold a program instruction or an item of data)

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11
Q

State what is meant by the term ‘memory address’.

A

A pointer to a location in memory

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12
Q

Main memory is volatile.

Describe what is meant by this.

A
  • Power is needed to retain its contents
  • When the computer is switched off, its main memory is completely wiped
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13
Q

Why is main memory classed as primary storage?

A

The CPU has fast, direct access to it

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14
Q

Why is main memory often referred to as random-access memory?

A

The storage locations can be read from and written to in any order

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15
Q

Give some characteristics of random-access memory (RAM).

A
  • Stores currently executing programs and data
  • Volatile - if a computer loses power, all data stored in its RAM is lost
  • Not suitable for long-term storage of software/data
  • Contents of RAM can be manipulated while computer running
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16
Q

Give some characteristics of read-only memory (ROM).

A
  • Memory that cannot be changed by program or user
  • Retains its memory after computer turned off - its contents are permanently embedded
  • Used to store instructions/software for the computer to boot up when turned on - e.g. BIOS
17
Q

Give some characteristics of cache memory.

A
  • Cache memory stores commonly used instructions and is used to speed up processing
  • Cache located on same microchip as CPU, so can be accessed much quicker than ordinary RAM
  • Executing a program from cache memory means it runs more quickly
  • Computers don’t have much cache memory because it is much more expensive
18
Q

Give some characteristics of virtual memory.

A
  • It’s an area on a secondary storage device used to store programs if you do not have enough physical memory to store them
  • Programs that are open but not currently active are transferred to virtual memory to make room in main memory
  • Not physical
19
Q

Give some characteristics of flash memory.

A
  • Physical, secondary storage devices
  • Non-volatile storage
  • Solid state technology, so non-mechanical
  • More reliable and durable than alternatives - can only be overwritten limited number of times
20
Q

Describe the function of the control unit (CU).

A
  • Handles all processor signals
  • Controls flow of data within the system
  • Fetches instructions from memory sequentially, decodes them and directs operations of other parts of the system to execute them
21
Q

Describe the function of the arithmetic logic unit (ALU).

A

Performs arithmetic and logic operations on data

22
Q

Describe the function of the clock in a computer system.

A
  • Controls the rate at which program instructions are executed
  • Each ‘tick’ of the clock triggers the CPU to carry out one action
  • Its speed is measured in cycles per second: 1Hz = 1 cycle per second

(Modern CPUs have clock speeds of around 3GHz)

23
Q

What are general-purpose registers in a computer system?

A

Direct-access storage which temporarily stores data and instructions within the CPU

24
Q

The fetch-decode-execute cycle is the cycle the central processing unit (CPU) follows in order to process instructions.

Name two registers used in the cycle.

A

Any two from:

  • Program counter / PC
  • Current instruction register / CIR
  • Memory address register / MAR
  • Memory data register / MDR
  • Accumulator / ACC
25
Q

Describe the function of the program counter (PC).

A
  • Holds the memory address of the next instruction to be fetched from main memory
  • Memory address incremented during the fetch process
26
Q

Describe the function of the current instruction register (CIR).

A

Holds the instruction currently being executed or decoded

27
Q

Describe the function of the memory address register (MAR).

A

Holds the memory address of current data that is to be fetched from memory

28
Q

Describe the function of the memory data register (MDR).

A

Holds data found at memory address held in MAR, or data that is to be transferred to main memory

29
Q

Describe the function of the accumulator (ACC).

A

Holds the result of a calculation performed by the ALU

30
Q

What is a core within a computer system?

A

A processing unit within the CPU, containing an ALU, control unit and registers

31
Q

What is a bus within a computer system?

A

A collection of wires that is used to transfer data between the CPU, main memory and input/output devices

32
Q

Give the 3 types of buses used in a computer.

A
  • Control bus
  • Address bus
  • Data bus
33
Q

Describe the function of the control bus.

A

Carries signals from the processor between the components of the CPU and other parts of the computer system

(bidirectional)

34
Q

Describe the function of the address bus.

A

Holds the address of the memory location that the CPU will read from or write to

(unidirectional)

35
Q

Describe the function of the data bus.

A

Transfers program instructions and data between memory and the CPU

(bidirectional)

36
Q

(Exam-style question)

Describe how the width of the address bus determines the size of the memory that a CPU can use. (3)

A
  • Each memory location has a unique binary address
  • Each wire in the address bus represents one bit of the address
  • Therefore, the number of wires it has determines how many unique addresses can be generated
37
Q

(Exam-style question)

Describe one reason the data bus needs to be bi-directional. (2)

A

The CPU needs to be able to read program instructions and data from memory and write the results of operations to memory

38
Q

(Exam-style question)

Describe how program instructions stored in memory are processed by the central processing unit. (3)

A
  • Instructions are fetched from memory into the CPU one at a time, where they are decoded and executed by the control unit (CU)
  • Arithmetic and logic operations are performed by the ALU
39
Q

Describe what happens in each stage of the fetch-decode-execute cycle.

A

Fetch -

  • Memory address of current instruction held in program counter is copied into MAR
  • Address in program counter is then incremented by one - program counter now holds address of next instruction
  • Processor sends signal containing memory address of current instruction along address bus to main memory
  • RAM retrieves instruction/data stored at that address and passes it back along the data bus to MDR - instruction is then copied into CIR

Decode -

  • Control unit (CU) reads contents of CIR, checking if it is a part of its instruction set

Execute -

  • Instruction held in CIR is then decoded and executed by CU - the results of processing are stored in ACC

IGCSE Edexcel Computer Science (23 decks)

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