Hardware

Hardware

1. Stored programs: the von Neumman model

   • 1930s and 40s: idea of general-purpose computers developed
   • Alan Turing and John von Neumann
     • proposed the instructions for the process could be held in a storage with the input data
   • stored-program/von Neumann architecture computer
     • processing instructions stored in memory with the data
       • written as binary numbers
     • components
       • Central Processing Unit (CPU)
         • hardware device doing the processing
       • Arithmetic/logic unit (ALU)
       • main memory/Random-Access Memory (RAM)
         • storage
       • connected by buses
   • when a computer is turned on, the CPU fetches instruction from memory, carries it out and then fetches the next, and so on.
     • fetch-decode-execute cycle

2. Hardware components of a computer system RAM and ROM

   • Read-Only Memory(ROM)
     • non-volatile
     • firmware
       • programs permanently stored
         • all and carries out specific tasks
           • (i.e. initialising hardware components and starting operating system when computer is switched on)
       • BIOS
         • Basic Input/Output system
       • UEFI
         • Unified Extensible Firmware Inferance
         • replaced BIOS
   • RAM
     • temporary store for data and instructions
     • usually in GB
     • volatile
   • writing
     • CPU saving data into memory
   • reading
     • CPU must specify which part of memory to read (get data) from
   • each memory location has a unique memory address
     • labelled with numbers (starting from 0)

3. Fetch-decode-execute: in detail

   • ALU (Arithmetic/Logic Unit)
   • registers
     • some with specific roles
       • accumulator
       • program counter
       • current instruction
   • steps in cycle controlled by control unit
   • steps in cycle synchronised by electronic clock
   • buses
     • address
     • data
     • control
   • 1.fetch
     • memory receives signal and looks up its' location before copying the data onto the data bus
   • 2.decode
     • control unit analyses the contents and signals the other components what to do
   • 3.execute
     • instruction is completed by CPU

4. Cache memory

   • third kind of main memory
   • small amount of fast, expensive memory used in-between two devices that communicate at different speeds (CPU and RAM)

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