3. hardware

CPU architecture

- processor (consists of the ALU)
- control unit (controls operation of the memory, processor and input/output devices)
- ALU (carries out logic systems)
- system clock (used to produce timing signals on the control bus)

Busses

- carries data through components
- address bus (unidirectional)
- data bus (bi-directional)
- control bus (unidirectional and bi-directional)

Immediate access store

holds data and instructions when they are loaded from the main memory and waiting to be processed

Current Instruction Register (CIR)

- increments value of instructions by 1
- fetches the data and instructions

Memory Address Register (MAR)

- stores address of instruction, copies it and sends to the MDR

Memory Data Register (MDR)

- stores data from address received from the MAR
- sends it to the CIR

Program Counter (PC)

- increments value of instructions by 1
- fetches the data and instructions

Accumulator

- during calculations, data is temporarily held in it

Fetch-decode-execute cycle

1. PC contains address of next instruction
2. address copied from MAR via address bus
3. fetched instruction temporarily stored in MDR
4. instruction moved from MDR to CIR
5. PC incremented by 1 for next instruction
6. fetched instruction decoded and executed

System clock

controls the speed at which instructions are processed

Clock speed

dictates how many instructions the CPU can process each second

Issues of increasing clock speed

- operations become unsynchronised and computer can crash
- overheating of CPU

Cache memory

memory that is used to store recently accessed or frequently accessed data so that the CPU can retrieve it quickly

Advantages of using many cores

faster performance

Disadvantages of using many cores

multiple cores attempt to access or modify the same data at the same time, causing delays due to contention

Embedded systems

Special-purpose software designed and included inside a larger system

Input devices

enable the user to input data and commands into the computer

Examples of input devices

- 2D scanners
- 3D scanners
- mouse/trackball
- microphones
- touchscreens (capacitative, infra-red, resistive)
- sensors

Sensors

- acoustic: sound
- accelerometer: acceleration
- flow: fluid movement
- gas: gas concentration
- humidity: moisture level
- infra-red (active): amount of infrared light
- infra-red (passive): heat emission
- level: position or quantity
- light: brightness
- magnetic field: magnetic strength
- moisture: water content
- pH: acidity or alkalinity
- pressure: force per unit area
- proximity: object detection
- temperature: hotness or coldness

Control of street lighting

- light sensor sends data to ADC
- digitises data and sends it to microprocessor
- microprocessor samples data every minute
- if data from sensor < value stored, signal is sent from microprocessor to street lamp, lamp is switched on

Output devices

- actuator
- inkjet printer
- laser printer
- liquid crystal display (LCD) screen
- light emitting diode (LED) screen
- digital light processing (DLP) projector
- liquid crystal display (LCD) projector
- speaker/headphone
- 3D printer

Inkjet vs. laser printer

Inkjet printer:
- uses liquid ink sprayed onto the paper through tiny nozzles
- good for printing high-quality colour images and photos
- slower printing speed
- ink cartridges may need frequent replacement

Laser printer:
- uses toner powder fused onto the paper using heat and pressure
- ideal for printing text-heavy documents
- faster printing speed
- toner cartridges last longer than ink cartridges
- generally better suited for printing in high-volume

LCD vs LED monitors

LCD:
- uses liquid crystal display technology
- requires a separate backlight
- thicker and heavier
- lower energy efficiency
- limited colour accuracy and viewing angles

LED:
- uses light-emitting diode technology for backlighting
- thinner and lighter
- higher energy efficiency, often consuming less power
- improved colour accuracy and wider viewing angles
- more durable

Primary storage

- directly accessed by the CPU
- e.g. RAM, ROM, cache memory

Secondary storage

- not directly accessed by the CPU
- e.g. HDD, SSD, DVD, memory stick, Blu-ray disc

Off-line storage

- can be physically moved away from a device and stored somewhere else
- e.g. CD/DVD, Blu-ray disks, USB flash memories, cloud storage

Random Access Memory (RAM)

- data that needs to be stored or accessed immediately
- volatile
- used to store data and files
- can be written to or read from and can be changed
- larger RAM size, faster computer
- if RAM becomes full, processor has to overwrite old data on RAM

DRAM vs. SRAM

DRAM:
- needs to be constantly refreshed
- less expensive to manufacture
- higher memory capacity
- consumes less power

SRAM:
- doesn't need to be constantly refreshed
- faster data access time

Read Only Memory (ROM)

- non-volatile
- used to store start-up instructions
- can only be read and cannot be changed

Virtual memory

- space on a hard disk or other storage device that simulates RAM
- HDD or SSD

Magnetic storage

- uses platters which are divided into tracks and sectors
- date is read and written using electromagnets
- e.g. HDD

Optical storage

• moving lasers shone at disk to create and read pits and lands

• e.g. - e.g. CD/DVD, Blu-ray disks

Solid-state (flash memory)

- uses NAND or NOR technology
- transistors are used as control gates and floating gates
- e.g. SSD

Cloud storage

- same data is stored on more than one server in case of maintenance or repair
- can be accessed remotely in comparison to storing data locally

Network Interface Card (NIC)

allows a device to connect to a network

Media Access Control (MAC)

- NIC is given a MAC address at the point of manufacture
- usually written as hexadecimal
- created using the manufacturer code and the serial code

Internet Protocol (IP)

- protocol for sending data across the internet that assigns unique numbers to each connected device

Static vs. dynamic IP

Static IP addresses:
- assigned manually to a device
- does not change over time

Dynamic IP addresses:
- assigned automatically to a device
- changes periodically or when device connects to a different network

IPv4 vs. IPv6

IPv4:
- widely used protocol

IPv6:
- removes the risk of IP address collisions
- has built-in authentication checks
- allows for more efficient packet routes

Router

- sends data to a specific destination on a network
- can assign IP addresses
- can connect a local network to the internet