Hardware

Hardware

1. Elements of a computer

2. Primary Memory

   • Read Only memory (ROM)
     • NON Volatile
       • Holds simple operating system (BIOS) as it is burned on chip wwhen computer is made
         • BIOS
           • Basic imput and Output system
             • Runs a 'bootstrap loader' that looks for another operating system on the hard drive to load in to RAM
   • Random Access Memory (RAM)
     • It is volatile
       • Holds program instructions and data that is being edited.
         • To execute a program it must be loaded from backing store to RAM as it is faster.

3. External Backing Store

   • includes SSD's, usb flash memory, SSD's and DVD's
     • Mechanical storage is chaper but slower
       • SSD's have no moving parts and are fast but expensive
         • Theese are all usually slower and cheaper than RAM

4. Bits, Bytes and Words

   • Computers pass info using digital signals which are set as voltages (o,5)
     • This digital code (machine code) has 2 values on and off (1,0)
       • When it reaches its destination the digital code is changed to its original info (decoding)
   • A bit is a binary digit
     • A byte is 8 bits
       • A kilobyte is 1024 bytes
         • A megabyte is 1024kb

5. Von Neumann Architecture

   • • Central processing Unit
       • Controls transmission of main data to and from memory
         • Process the data in memory
           • Controls transfer of data between input, memory and output
     • Control Unit
       • Fetches each instruction in sequence from memory
         • executes it by decoding it and sending control signals to other parts of the computer
     • Arthmetic Logic Unit (ALU) (inside the processor)
       • Carries out processing and manipulation of data
         • This normally consists of:
           • Arithmetic operations (+/-)
             • logical comparisons (AND,OR, XOR)
     • Registers
       • Temporary memory locations in the CPU
         • used when a program instruction is being carried out
           • Holds details of instruction being carried out
             • typically 12
     • Instruction Set
       • These are the set of all program commands typically available in the CPU

6. Special Registers

   • MAR (Memory address register)
     • MDR (Memory data register)
       • PC (program counter)
         • CIR (Current Instruction register)
           • The instruction most frequently fetched from memory
         • The address of the next program instruction to be read from memory
       • Holds the data read from (or being written to) memory
     • Holds the address of the memory location in use

7. Busses

   • Address Bus - used to specify the address in memory where the data will be read or written from
   • Data Bus - used to transfer data from memory to CPU (visa versa)
   • Control Bus - Used to send control signals between parts of the computer

8. RAM Cache memory

   • faster and more expensive than ram but speeds up the operation of the CPU
     • Its very small and usually in the CPU (100mb)
       • As data is read form the RAM it is copied over to the RAM Cache meaning data used more recently can be read quicker

9. Fetch Execute Cycle

   • This fetches the programs and instructions from memory.
     • Registers and devices that are used:
       • PC (Program counter) keeps track of the memory address that is to be executed next
         • MAR (Memory address register) this is a two way register that holds the data fetched from memory)
           • CIR (Current Instruction Register) - a tempory holding place for the instruction
             • CU (Control Unit) decodes a program instruction in the CIR
               • ALU performs mathematical operations and logical ones.

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