Computer hardware

Computer hardware

1. central processing unit (CPU)

   • carries out all the processing in a computer
     • arithmetic and logic unit (ALU)
       • carries out all of the arithmetic and logic operations
     • control unit
       • uses electrical signals to control flow of data within the CPU
   • fetch execute cycle
     • 3. Execute
       • the instruction
     • 1. Fetch
       • the instruction from memory
     • 2. Decode
       • decode instruction to figure out what processing to do
     • when the computer is switched on the CPU will look for a specific place in the ROM
       • to find the first program to load and execute
         • this is the boot sequence
           • afterwards the operating system provide programs for the CPU to run
             • the speed that the CPU can process data depends on
               • clock speed
                 • speed of fetch-execute cycle
                   • determined by electronic clock chip
                 • measured in cycles per second
                   • known as hertz (Hz)
                 • processor speeds measured in:
                   • gigahertz (GHz) billiojns of cycles per second
               • cache memory
                 • CPU can't access main memory at the same speed as the processor clock chip
                   • transferring data from main memory causes delays
                     • cache reduces time to access data
                 • expensive
               • multiple processor cores
                 • use multiple CPUs working together
                   • they can all fetch, decode and execute instructions at the same time
                     • more data processed simultaneously
                   • need more complicated operating systems
       • ROM- A store for data that cannot be overwritten
         • data here os always available
           • it's not lost when the computer is turned off
   • Random access memory RAM
     • main memory
       • stores data, applications and operating systems whilst in use
     • programs stored in cache memory
       • used to store data waiting to be processed
       • cache memory
         • fast memory located near the CPU with dedicated connections
           • has fast access to frequently used data
             • relatively expensive compared to RAM
     • RAM and cache are primary storage
       • part of computers processing capabilities
     • when off data is lost
   • Secondary storage
     • Non-volatile storage used to store programs and files that need to be kept even when the power is not on
     • examples
       • hard drives
         • flash memory
       • solid state drives
   • John Von Neuman architecture is the basis for all modern digital computers
     • all data and instructions are stored in RAM as binary numbers

2. memory

   • virtual
     • part of the hard drive
       • extension to RAM
         • used when there isn't enough RAM to hold all data and programs
     • data is passed between RAM and virtual memory
       • access to virtual memory is slower than to RAM
     • adding more RAM reduces use of virtual memory
       • which improves performance of the computer
   • flash
     • type of ROM
       • can be rewritten
     • portable for storing and transferring data
   • Bit: binary digit 0 or 1
     • byte: 8 bits
       • kilobyte: 1024 bytes
   • dynamic RAM
     • Static RAM
       • chips more complicated
       • don't loose charge
         • can store data without being refreshed
           • much faster used for cache memory
     • one transmiter and a capacitor
       • can hold a small charge
         • for a few milliseconds
           • to represent 1 bit

3. binary logic

   • all computers work in binary
     • logic circuits are used to make calculations
   • boolean algebra
     • method for expressing mathematically a logic circuit
       • helps use use facilities within programming languages
         • helps computer know what to do next

4. input and output devices

   • users with specific needs
     • foot mouse
       • limited hand movement
       • track ball device operated by the foot
     • Braille keyboard
       • keyboard with raised patterns on each key
         • which match braille characters
           • for blind and visually impaired to type text
     • voice input
       • those who find it difficult to operate a keyboard
         • spoken commands can be translated
     • joystick
       • limited movement
       • less physical movement than a mouse
       • guides pointer on a screen
     • eye typer
       • limited physical mobility
       • camera tracks movement of the eye
         • detect which key the user is looking at
     • puff suck switch
       • switch operated by blowing or sucking in a small tube
         • limited physical mobility
         • interprets which action to take
     • outputs
       • screen readers
         • read a computer screen
       • actuators
         • create physical movement in response to a command
       • voice synthesisers
         • spoken output

5. secondary storage

   • needed to store data and programs when power is switched off
   • magnetic hard disk
     • stores the operating system, stored programs and user data
     • They're
       • reliable
       • high capacity
       • low cost
   • optical disk
     • used to transfer files or distributing software
     • It's
       • good capacity
       • low cost
       • lightweight and portable
       • e.g cd
   • flash memory
     • personal portable file storage
       • used in hand held devices
       • more expensive than hard disk
       • good capacity
   • considerations
     • capacity
       • how much does it hold
     • speed
       • how quickly can data be transferred
     • portability
       • does data need ot be moved from one system to another
     • durability
       • if transported can it easily be damaged?
     • reliability
       • can it be used over again without failing

6. hardware

   • physical components of a computer system
     • anything that can be seen or touched
   • hardware components
     • include
       • input
       • output
       • storage
       • processing

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