Computing

• ALU: arithmetic logic unit.

  Performs arithmetic calculations

  Performs logic operations
• CU: Control Unit

  Controls the flow of data between registers

  Controls inputs and outputs within CPU
• CACHE:

  Stores frequently used instructions and data

  Built onto the CPU which provides quicker access to RAM
• PC (Program Counter):

  Stores the address of the next instruction
• MAR (Memory Address Register):

  stores the address of the next instruction to be accessed
• MDR (Memory Data Register):

  stores the data to be brought from or sent to main memory
• ACC (Accumulator):

  stores the value currently being worked on
• FETCH the next instruction and associated data from main memory
• DECODE and interprets the instruction
• EXECUTE the instruction
• The Purpose of the CPU

  • The CPU is the brain of the system.

  • Processes all the data and instructions to make the

  system work.

  • It is installed on the motherboard.
• The Purpose of Embedded Systems

  • To provide a specific, pre-defined function

  • Cheaper than providing a full personal computer system.

  • Can be made much smaller than a personal computer system

  • Allows for a device to be automated / programmed.
• The Characteristics of Embedded Systems

  • Task specific.

  • The task is performed in a certain time frame.

  • Do the same thing repeatedly.

  • Basic or no UI.

  • May respond to sensors.
• Clock Speed

  • A faster clock speed allows more instructions carried out per

  second and so instructions are executed more quickly.

  • This allows for more programs to be run at the same time.

  • This also allows for more complex processing operations to be

  completed in real time.
• Cache Size

  • A larger cache gives more space for frequently used instructions.

  • This provides more storage for fast access, meaning faster

  fetching of instructions and so faster processing
• Number of Cores

  • More cores allow more instructions carried out simultaneously.

  • More cores allow the processor to process more instructions at

  the same time.

  • This allows batches of instructions to be executed more quickly,

  which allows for more programs to be run at the same time.
• Lossless Compression:

  o Compresses data files without losing

  any of the information

  o Reversible - that the original data can

  be reconstructed

  o Not all files can be compressed in this

  way
• Lossy Compression:

  o Does lose some of the information

  o Used where this is acceptable e.g.

  audio

  o Produces smaller files

  o Poorer accuracy
• ROM (Read Only Memory)

  • Values stored in ROM remain when the computer is switched off (non volatile).

  • Virus attacks are unlikely.

  • Values stored cannot be accidentally changed.

  • Data is written permanently when the computer is built.

  • Holds the instructions for booting the computer.
• RAM (Random Access Memory)

  • Loses its data when the computer is switched off (volatile)

  • Used to save data about programs that are currently open.

  • Much faster than a HDD or SSD, and so the CPU has to spend less time in the "fetch"part of the "fetch-decode-execute".

  • It is more expensive per GB than a HDD or SSD. This limits our usage of RAM, and the amount that can be installed.
• Virtual Memory

  • Virtual memory is simulated memory that is written to a file on the hard drive.

  • It lets more memory be used than there is in the system.

  • This is useful when you need to run more applications on the computer

  than RAM can support.
• Optical Storage

  • Data is written and read using a laser beam

  • Examples include CDs and DVDs

  • Inexpensive, reliable, robust, relatively large capacity
• Magnetic Storage

  • Uses different magnetic patterns to store data

  • Examples include tape cartridge and hard drive

  • Large capacity, can be used to store operating system and other files and programs, reliable, cost-effective
• Solid State Storage

  • Data is stored within flash chips

  • Examples include USB drives and SSDs

  • Flexible, faster access to data, can be used for portable devices, generally smaller in size, robust, easy to use
• Resolution is the number of pixels in the image

  o Higher resolution = more pixels = clearer

  image = more space needed
• Colour depth is the number of bits used to store

  the colour for each pixel

  o 1 bit allows 2 values, 2 bits allow 4 values etc.

  o Higher colour depth = more realistic colours =

  more space needed
• • HTTP – HyperText Transfer Protocol – Web pages
• • HTTPS - Hypertext Transfer Protocol (Secure) – Secure web pages
• • FTP – File Transfer Protocol
• • SMTP – Simple Mail Transfer Protocol – Send emails
• • IMAP – Internet Message Access Protocol – Receive emails
• • POP3 – Post Office Protocol version 3 – Receive emails
• • DNS – Domain Name System – Converts names to IP Addresses
• • IP – Internet Protocol – Addresses packets
• • TCP – Transmission Control Protocol – Provides reliable transmission
• The Internet – A worldwide collection of computer networks
• Hosting – A service which allows you to publish a website to The Internet
• DNS (Domain Name System) – A system for converting host names and web addresses into IP addresses
• Web Server – A server configured to host websites.
• Web Client – A client accessing websites, usually over The Internet.