Hardware

Hardware

1. The CPU

   • CPU
     • Central processing unit
     • The CPU is the brain of the computer
     • Its job is to process data inputted and execute an output
   • The fetch-execute cycle
     • The CPU follows a process known as the fetch-execute cycle this has 3 stages
     • Decode:
       • This is when the CPU works out what it needs to do.
       • It then gets what it needs to carry out the instruction
     • Fetch
       • the CPU "fetches" data or instructions from the main memory (RAM) then storage it in its own temporary storage
         • It's all done in binary
         • When the data travels from the CPU to the RAM/memory it travels o. The address bus
         • When data is returning from the RAM/memory to the COU it travels on the data bus
     • Execute
       • This is when the command is then completed and carried out.
   • Areas of a CPU
     • Control unit
       • This makes sure the right data goes to the correct hardware
     • Immediate access store (ISA) or "cache"
       • This is faster then ram
       • This is when the data is being immediately processed
     • Arithmetic and logic unit
       • The arithmetic part does all the maths
       • The logic part deals with logical operations such as true/false
   • Clock speed
     • How fast the fetch-execute cycle is done
     • To find out how fast the process is being does we use the clock chip in the CPU
     • It's measured in hertz
       • GHz=billion MHz=million
     • Over clocking
       • When you increase the clock speed

2. Input and output devices

   • Normal input devices
     • Keyboard
     • Mouse
     • Touch screen
     • Microphone
   • Normal output devices
     • Monitor
     • Printer
     • Speakers
   • Input devices for disabled
     • Eye Typer
       • Good for people with low physical mobility
     • Foot mouse
       • Good for people with limited hand movement
     • Braille keyboard
       • Good for people with visual impairments
   • Output devices for disabled
     • Plotter
       • Good for people that don't have great eyesight

3. Memory

   • Cache memory
     • The CPU can't always use main memory especially when executing instructions this make it very slow
     • The cache memory helps the computer quickly carry out commands
     • The computer might have (e.g 8GB) but the cache will always have a smaller memory (e.g 2GB)
   • RAM
     • Random Access Memory
     • Volatile, meaning data is lost when the power is off
     • Stores programs being used by the computer
     • Contains an operating system
     • Large amount of space (4GB or more on a normal computer)
     • Can re-wirte
   • ROM
     • Non-volatile
     • Contains the boot sequence
     • Stores data to start the computer
     • Small space (1 or 2 MB)
     • Can't re-write
   • Virtual memory
     • An extension to the RAM. It's used when there is not enough RAM to hold all the data
     • Data is passed between RAM and virtual memory
     • Slower then RAM
   • Flash memory
     • A type of ROM it can't be re-written
     • It's used as a portable medium for storing and transferring
     • It advances in processor technology, mobile internet access and low power
     • It's a high capacity storage such as solid state

4. Binary logic

   • NOT gate
     • 1 = 0 0 = 1
     • Triangle with a little circle on the nose
   • AND gate
     • 0+0=0 0+1=0 1+0=0 1+1=0
     • Rounded edge
   • OR gate
     • 0+0=0 0+1=1 1+0=1 1+1=0
     • "Arrow" head
   • NAND
     • 0+0=1 0+1=1 1+0=1 1+1=0
     • Same as AND gate but little circle on the nose
   • NOR gate
     • Same as OR gate but with a circle on the nose
     • 0+0=1 0+1=0 1+0=0 1+1=0

5. Secondary storage

   • Magnetic
     • Data can be stored and retrieved easier, stored in binary, used mostly for computers
     • Reliable, high capacity, low cost
     • A magnetic hard disk stores the operating system, installed programs.
   • Optical
     • Good capacity, low cost, light weight and portable
     • Optical is excellent for transferring files
     • Optical is used for CDs + DVDs, small indents are made to store data
   • Solid state/ flash memory
     • Used for flash memory (USB)
     • Good capacity, used in hand held devices, more expensive than a hard disk
     • Consumes little power