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Hexadecimal

A base-16 numeral system that uses sixteen distinct symbols: 0-9 and A-F.

Why use hexadecimal?

Hexadecimal allows representation of 16-bit words with only 4 digits, taking less display space, and is quicker to enter.

Hexadecimal in color coding

Colours in web design are often represented in hexadecimal format, where # indicates a colour code, e.g., #FFFFFF for white.

MAC Address

A Media Access Control address is used to uniquely identify devices on a network, formatted as six pairs of hexadecimal digits.

IPv6

Internet Protocol version 6 uses hexadecimal addressing to provide enough unique addresses for every networked device.

Hexadecimal in programming

Hexadecimal simplifies low-level programming by making it easier to reference memory addresses compared to long binary strings.

Error messaging

Hexadecimal error codes are used in embedded systems for compact display on small screens, aiding in troubleshooting.

Conversion from hex to binary

Hexadecimal digits can be easily converted back to binary, facilitating data representation.

Color intensity in hex

The value of hexadecimal numbers represents color intensity in web design, allowing a full spectrum of colors.

Software

A set of programs/instructions written in a programming language performing 1 or more tasks to tell the computer what to do. It allows the computer to function.

Hardware

The physical and peripheral components of a computer.

Firmware

A software permanently stored on the hardware/ROM which contains instructions allowing the hardware to function and communicate with software.

Bootloader

A small piece of firmware containing the instructions to start up the operating system; it loads the OS onto the RAM upon startup.

How do applications access hardware resources?

Through making 'calls' to the OS and the device drivers.

System software

The manager: A variety of programs which are necessary for the computer to function and manages the operation of computer hardware and software.

Application software

The software which the user needs to perform specific tasks using the computer's resources.

Operating system

The platform in which other programs/applications are run on. Also provides the user with a human computer interface.

• Allocates the hardware's resources

Utility Software (MMC)

Manages, maintains, and controls the computer's resources. It makes sure everything runs smoothly.

Interrupts

A signal sent from a device or a software to the OS which causes a temporary stop in the current instruction being processed to service the interrupt.

What are interrupts sent through?

Interrupt Request Lines (IRQ)

What are interrupts sent to?

The interrupt handler in the OS to perform the Interrupt Service Routine (ISR)

Examples of Interrupts

• Dividing by 0
• Hardware faults like no paper in printer
• Hardware interrupts like keyboard presses

High Level Language (HLL)

Programming language written in a language (like English) that humans understand. It is a portable language which can be used on multiple platforms (machine independent).

Low-Level Language (LLL)

Programs written for a specific type of architecture and hardware. It is non-portable and machine dependent.

Advantages and Disadvantages

• Debug ease
• Hardware (directly manipulates or machine independent)
• Ease of writing/understanding
• Memory space taken up (1 line = 1 machine or many lines of abstraction?)
• Speed of execution

Assembly language

A low-level language, it uses mnemonics to specifically manipulate hardware. 1 line of assembly language translates to 1 line of machine code.

• Difficult to debug

• Mnemonics

• Directly manipulates hardware

  Ex. Bootstrap in ROM

Assembler

Translates assembly language into machine code. Assembly language generally takes up less memory space than high level languages.

Advantages of Assembly language

• Uses less space in memory
• Faster processing speed
• Therefore is more efficient overall
• Directly manipulates hardware

What is a compiler?

A compiler is a software program that translates source code written in a high-level programming language into machine code that can be executed directly by a computer.

• Compiles and translates the entire file at once
• Produces an executable file specific to computer architecture
• If a syntax error is encountered, the compiler doesn’t produce an executable file, and sends out an error report

What is an interpreter?

A software program which translates high-level language into machine code line-by-line

• If a syntax error is encountered, it stops translating at that line and sends out an error report
• Code must be retranslated each time it is run

Advantages of a compiler

• Produces an executable file, so users can’t see or edit the source code for stealing
• Only needs to be translated once, so it’s faster to run
• User doesn’t need to have interpreter installed to execute the code

Advantages of an interpreter

• Faster and easier to debug during the development process, as users can clearly see where the error was made

Integrated development environment (IDE)

A program which allows users to write, debug, and translate code

Consists of: Prettyprint, Run-time environments, Code editors, Autocomplete and autocorrect, Translators, and Error Diagnostics

Code editors

Used to write and edit program code

• Makes the code clearer, to make editing easier for programmers
• Prettyprint, Syntax highlighting, Indentation, Line numbers, Autocorrect and complete

Run-time environments

The facility of the IDE which runs programs

• Allows users to test code
• Gives useful reports as to errors or program crashes

Prettyprint

Applying formatting and indentation to make the code easier to read

Error Diagnostics

A list of errors and their line numbers reported after testing

• Helps find mistakes made by the programmer. 
• Errors are identified along with the line number.
• The code may be underlined or highlighted.

Auto correct

Replaces/corrects any grammatical errors or variable names which have minor typing errors

Autocomplete

Provides a drop down list of variables/possible choices to complete keywords/variables

Translators

Allows the user to run the code using compilers and interpreters

What does the system software do?

• Helps maintain good working order of the computer so it runs without problems.
• Provides a platform to run other software. 
• Controls allocation and usage of hardware resources. 

Provides a Human Computer interface (HCI)

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

Binary system

a number system with base 2

Denary system

a number system with base 10

Hexadecimal

a number system with base 16

'A' in hexadecimal system is _ in denary

10

Overflow

error where the number of bits is not enough to hold the solution

Logical shifts

moving a binary value to the left or to the right, emptied bit is 0

Two's complement

method used to present negative values in binary

MSB is replaced from ______ to ______ in two’s complement

128 to -128

Uses of hexadecimal system

• defining colours in HTML
• MAC addresses
• IP addresses
• assembly languages and machine code
• debugging
• display error codes
• memory dumps

ASCII

7-bit code that represents letters, numbers and characters found in a standard keyboard as well as 32 control codes

Unicode

character code that enables most of the languages of the world to be symbolised with a special character identification

How is sound recorded?

• amplitude of sound wave is determined at set time intervals
• value is converted into digital form
• each sample is encoded as a series of binary digits
• series of readings gives the approximate sound wave

Sampling resolution (bit depth)

number of bits per sample

Increasing sampling resolution…

• increases accuracy of sampled sound as more detailed is stored about the amplitude
• increases memory usage as more bits are being stored

Sampling rate

number of sound samples taken per second in Hz

Increasing sampling rate…

• more accurate sound
• fewer estimations

Bitmap images

made of pixels stored in a computer as a series of binary numbers

Colour depth

number of bits representing each colour

8-bit colour depth

each pixel can be one of 256 colours