1.1: Systems Architecture

Difference Between Embedded Systems and General Purpose Computers

Embedded systems have limited functions and one program; general purpose computers can perform various tasks with different programs.

Microcontroller/Microprocessor

A single microchip with all computer components in one package.

Components in Microcontroller/Microprocessor

CPU, RAM, ROM, Input and Output Interface.

Benefits of Integrating Components in Microcontroller

Cheaper, more reliable, smaller, use less power

Embedded System

A computer system that performs a limited number of specific functions and is built into another device.

General Purpose Computers

Computers not embedded in another device, capable of various tasks with different programs.

Examples of Embedded Systems

Washing machine, Digital assistant, Smart TV, Supermarket checkout

Why Microcontrollers are Suitable for Embedded Systems

Microcontrollers make devices cheaper, smaller, and more power-efficient, ideal for controlling other devices.

Memory Addresses

Unique number that identifies each location in RAM.

Comparison of RAM and ROM

RAM: stores data and instructions, volatile, read/write, larger size.
ROM: stores boot-up instructions, non-volatile, read only, smaller size

Virtual Memory

Operating system moves programs and data from RAM to hard disk when RAM is full.

How Virtual Memory Works

Operating system swaps unused programs/data to hard disk, retrieves when needed, may cause delays

Need for Virtual Memory

Prevents 'memory full' error when RAM is filled with running programs and data

Main Memory

Electronic circuit that stores information

Purpose of Main Memory

Store running programs and currently used data for CPU access

Other Names for Main Memory

Primary storage, primary memory

Types of Main Memory

RAM - Random Access Memory, ROM - Read Only Memory

Characteristics of RAM

Volatile, fast for CPU, consistent speed for data access

Content Stored in RAM

Running programs, currently used data, operating system

Characteristics of ROM

Read-only, data put in factory, non-volatile, fast for CPU

Content Stored in ROM

1. Boot-up instructions.
2. Basic instructions for input/output devices (BIOS)

Speed

How fast a secondary storage device can read and write data.

Durability

How robust a secondary storage device is likely will be.

Reliability

The length of time which a secondary storage device will work as it should.

Hard Disk Drive

A magnetic storage component with a very large capacity.

CD

An optical storage component with a capacity of 700MB.

DVD

An optical storage component with a capacity of 4.7GB.

Blu Ray Disc

An optical storage component with a capacity of 25GB.

Solid State Drive

A solid state storage method with a high capacity and transfer speeds.

SD and Micro SD Card

A solid state storage device which is used in cameras and phones.

Magnetic storage

Storage technology that uses the magnetic properties of materials to store data permanently.

Optical storage

Storage technology that uses laser light to store and read data permanently.

Solid state storage

Storage technology that uses flash memory to store data permanently.

Capacity

The amount of data that can be stored on a secondary storage device.

Cost

The price of a secondary storage device.

Portability

How easy it is to move a secondary storage device from one location to another.

Magnetic Tape

An magnetic storage method, usually packaged in a cartridge or cassette

USB Memory Stick

A solid state storage device which is very portable.

Content of RAM

Instructions of the programs that are currently running.
Data that is currently being used.

Stored Program Concept

Storing the program instructions and data in main memory.

Von Neumann Architecture

The fundamental design of computers where a CPU accesses main memory directly and uses secondary storage for long term storage of programs and data.

Control Unit

Sends signals to the other components to coordinate and control the CPU.

Registers

Very small, very fast memory locations inside a CPU that stores a single instruction or item of data as they are processed.

Fetch-Execute Cycle stage: Fetch

The CPU gets the next instruction in the program from main memory.

Fetch-Execute Cycle stage: Decode

The CPU understands what it has to do follow the current instruction.

Fetch-Execute Cycle stage: Repeat

The CPU decides what instruction is next and repeats the cycle.

Control Unit role in Fetch-execute Cycle

Controls the whole fetch-execute cycle
Decodes the current instruction.

Arithmetic Logic Unit (ALU) role in Fetch-execute Cycle

Executes instructions that need mathematical (e.g., add) or logical operations (e.g., and).

Cache role in Fetch-execute Cycle

Stores frequently used instructions and data, so that they can be fetched more quickly.

Program Counter Register

Stores the memory address of the next instruction to be fetched by the CPU.

Memory Address Register (MAR)

Stores the memory address of the instruction (or data) currently being read from or written to memory.

Memory Data Register (MDR)

Holds the actual instruction or data currently being read from or written to memory.

CPU

Central Processing Unit

Purpose of CPU

To processes instructions.

Arithmetic Logic Unit (ALU)

Component of a CPU that performs calculations and logic operations.

Cache

A small amount of memory inside the CPU used to store frequently used instructions and data that can be accessed faster than from main memory.

Fetch-execute cycle

The sequence of steps operated by a CPU to process instructions one by one.

Fetch-Execute Cycle stage: Execute

The CPU actually carries out the current instruction.

7-word summary of Fetch-Execute Cycle

Fetch Instruction, Decode Instruction, Execute Instruction, Repeat.

Accumulator Register

Holds the results of arithmetic and logic instructions at the end of the execute phase.

CPU Clock

A signal inside the control unit that cycles on and off very quickly and synchronises CPU operations.

Effect of Faster Clock

The fetch-execute cycle repeats more quickly with a faster clock speed.
So more instructions are processed per second.

1 Gigahertz

1 billion clock cycles per second.

CPU Core

A CPU within a CPU.
Each core operates its own fetch-execute cycle
A CPU with multiple cores can execute instructions in parallel.

Parallel Execution

Multi-core CPUs can execute more than one instruction at the same time through parallel execution.

Dual Core Parallel Execution

A dual-core CPU can execute 2 instructions at a time.

Quad Core Parallel Execution

A quad-core CPU can execute 4 instructions at a time.

Multi-Threaded Programming

Allows a single program to use more than one core by dividing tasks into smaller ones, enabling them to run on separate cores.

CPU Cache

A small amount of fast memory located inside the CPU, larger than registers but smaller and faster than main memory (RAM).

Stored in CPU Cache

Frequently used instructions, such as those inside a loop, are stored in the CPU cache.

Cache Impact on CPU Performance

Frequently used instructions can be fetched more quickly from the cache, making the fetch-execute cycle faster and increasing the number of instructions executed per second.

Effect of Cache Size on Performance

The larger the cache, the more likely instructions can be fetched from it, potentially improving CPU performance.

Unit of Measure for Clock Speed

Hertz, the number of clock cycles per second.

Single Core Parallel Execution

A single-core CPU can execute 1 instruction at a time.

Eight-Core Parallel Execution

An eight-core CPU can execute 8 instructions at a time.