Computers - Hardware

Stored Program Concept

• Early computers had a single function and needed to be rewired or rebuilt for different functions

• RAM holds the programs instructions/ data

• The CPU contains the control unit and arithmetic logic  unit used to carry out the instructions

• The address bus holds the address in memory and the contents are passed to the data bus

  FDE and CPU

• FDE cycle  contains Fetch, Decode and Execute

   - Instructions and data are stored in the memory

   -Instructions are fetched one at a time into the processor

   -The instructions are decoded by control unit

   -The instructions are executed, sometimes using the arithmetic logic unit

• The CPU is like a brain

• The processor carries out instructions (executes instructions)

   

Busses and Memory

• Instructions and data are stored in RAM until they are needed by the CPU

• Each instruction and item of data is stored in a location in memory

• Each element of the memory has a unique address

• The CPU is connected to other components using a bus

• There are 3 busses, Data, Control and Address Bus

• The Control and Data busses are bidirectional - 2 way information/data transfer

• But the Address Bus is unidirectional - only 1 way

• RAM (main memory) sits close to the CPU

• The data bus carries data between memory and CPU

• The control bus carries control signals

• The address bus carries the address of a memory locations

Secondary Storage 1

• RAM's contents are erased when its power supply is turned off, so everything gets moved to secondary storage

• There are 3 main types of storage technology: magnetic, optical, solid state

• Magnetic - HDD, Tape Drive

• Optical - DVD, CD

• Solid State -  SSD, USB

• Magnetic uses the polarization of particles on a disk to represent 1s and 0s

• Optical uses a laser and the pits and lands on the surface of a disk to represent 1s and 0s

• Solid State uses electrons forced into pools to represent 1s and 0s

Secondary Storage 2

• Capacity is measured in Mebibytes, Gibibytes and Tebibytes

• Speed refers to how fast data can be written to and read from a device

• Portability means how much movement the device can be subjected to without causing damage to the device or the data it contains