hardware (3)

• tracks (on HDD)

  surface divided into concentric circles.

  sectors (which are part of tracks( = smallest storage units on disk
• read / write head (on HDD)

  an actuator. moves head to desired track (on platter).

  changes magnetic orientation of material to write / read data.

  always moves- looking for correct sector
• platters (on HDD)

  circular, rigid disks - made of glass / aluminium layer of magnetic material
• secondary storage


  semi - permanently, doesn't last forever.

  not directly accessible by CPU.

  examples - magnetic drives (HDD), solid statedrives (SSD), optical disks(blue-ray, DVD)
• ROM, read only memory


  non volatile - contents stay when power off.

  contents cant be changed or edited only readable.

  contains starter instructions when computer first turns on
• RAM, random access memory

  more RAM the faster it is, it is expensive.

  can be written to / read from data, can be changed by user at anytime, stores data.

  volatile - when a device turns off, all the contents is lost.

  random - any memory address at anytime - not specific
• primary storage


  examples are RAM + ROM.

  it is directly accessed by CPU.

  has a smaller memory storage than secondary storage
• sensors

  input devices. used to measure properties of environment.

  it translates analog signals into digital signals, something a computer can read
• laser printer (output device)

  uses toner cartridges (contains powdered, electro-optically charged ink) with a laser mirror image of printer page is drawn onto a drum by creating negatively charged areas, then the drum picks up positively charged ink particles + bonds with paper by heat.
• advantages of laser printer


  higher quality than ink jet, fast, accurate, low running costs, used in schools
• uses of laser printer 


  creates physical copies of digital documents
• ink jet (output device)


  force tiny drops of ink through a fine nozzle onto sheet of paper to replicate a digital document
• use of ink jet


  creates physical copies of online documents
• advantages of ink jet


  its small, on scale printing, can be used for personal use, printing of a photograph
• address bus

  one way system (unidirectional), MAR -> RAM, carries datas address
• data bus

  two ways (bidirectional), MDR -> <-RAM, carries actual data
• control bus

  bidirectional, CU -><- RAM, command + control signals
• buses


  allows components to transfer data between another
• CIR

  centre instruction register. its responsible for holding current instruction
• CU

  control unit. controls all of instructions/data (operations) in CPU
• MAR

  memory address register. holds address of current instruction (in RAM)
• MDR

  memory data register. holds actual data stored in RAM, holds until CPU needs the data
• ALU

  arithmetic logic unit. logic operations, shift operations, arithmetic operations. between RAM + accumulator
• accumlator


  type of general purpose register.

  hold the result of a calculation, it is temporary stored.

  doesn't go to main memory and clog it up
• PC

  program counter.

  a special purpose register.

  holds memory address of next instruction to be executed. always incremented by 1.
• stored program concept

  von neumann architecture.

  instructions and data stored together in same memory.

  it is cheaper, quicker and more efficient
• CPU


  central processing unit.

  brain of the machine.

  fetch, de-code, exicut instructions
• digital camera (input device)

  light enters camera and falls onto sensor made up of millions of pixels. each one measure the light intensity, and a processor converts these values into digital data. to represent colour values.
• advantages of a digital camera

  can replace film cameras, they are instant, you can share photos online
• barcode scanner (input device)

  shines a red laser at barcode, the white lines reflect the light back to scanner, the black lines absorb + reflect less light. each line is interpreted by processor + goes into binary values
• advantages of barcode scanner

  quicker queues, reduces human errors, automatic stock control
• core

  number of processors on CPU. more cores = able to do different things at the same time
• clock speed


  1 cycles per second = 1 Hertz = 1 instruction carried out each second. faster clock speed = faster computer system
• cache memory

  CPU -><- cache-><-RAM. small expense. frequent memory accesssed - less buses to get to it. faster than RAM
• embedded system

  a single microprocessor that includes RAM, ROM, CPU.

  devices wouldn't be able to preform specific function without it
• instruction set

  list of instruction than can be reorganised and executed by CPU
• touch screens

  resistive, infrared, capacitive
• resistive


  has 2 conductive layers. top layer is flexible material and layers are separated by insulating layer. when screen pressed it makes layers contract this complex the circuit
• uses of resistive touch screen


  cash machines, medical equipment, information kiosks
• advantages of resistive touch screen


  it is cheap, can be activated with any object, resistant to surface contamination, however there is lower image clarity and precision