Hardware Flashcards by Jake ,./..

What is meant by the term ‘computer architecture’?

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

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Give the core elements used in von Neumann architecture.

Input & output mechanisms
Main memory
Central processing unit (CPU)

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John von Neumann proposed the concept of a stored program.

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

Program instructions
Data

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Describe the function of the central processing unit.

To decode and execute program instructions fetched from memory

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

A task that is carried out by the CPU

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(Exam-style question)

Von Neumann developed the stored program concept.

Describe the stored program concept. (2)

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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(Exam-style question)

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

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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(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)

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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Give some examples of input devices and output devices.

Input -

Keyboard
Mouse
Scanner
QR code reader
Sensor
Microphone
Touchscreen / tablet

Output -

Monitor
Printer
Projector
Speaker
Touchscreen / tablet

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Describe the characteristics of main memory.

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

A pointer to a location in memory

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Main memory is volatile.

Describe what is meant by this.

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

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Why is main memory classed as primary storage?

The CPU has fast, direct access to it

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

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

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

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

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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

Give some characteristics of cache memory.

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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

Give some characteristics of virtual memory.

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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

Give some characteristics of flash memory.

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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

Describe the function of the control unit (CU).

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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

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

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Performs arithmetic and logic operations on data

Describe the function of the clock in a computer system.

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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)

What are general-purpose registers in a computer system?

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

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.

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Any two from:

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

Describe the function of the program counter (PC).

* Holds the memory address of the next instruction to be fetched from main memory * Memory address incremented during the fetch process

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

Holds the instruction currently being executed or decoded

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

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

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

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

Describe the function of the accumulator (ACC).

Holds the result of a calculation performed by the ALU

What is a core within a computer system?

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

What is a bus within a computer system?

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

Give the 3 types of buses used in a computer.

* Control bus * Address bus * Data bus

Describe the function of the control bus.

Carries signals from the processor between the components of the CPU and other parts of the computer system | *(bidirectional)*

Describe the function of the address bus.

Holds the address of the memory location that the CPU will read from or write to | *(unidirectional)*

Describe the function of the data bus.

Transfers program instructions and data between memory and the CPU | *(bidirectional)*

# **(Exam-style question)** Describe how the width of the address bus determines the size of the memory that a CPU can use. (3)

* 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

# **(Exam-style question)** Describe **one** reason the data bus needs to be bi-directional. (2)

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

# **(Exam-style question)** Describe how program instructions stored in memory are processed by the central processing unit. (3)

* 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

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

**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**

Hardware Flashcards

(39 cards)