Computer hardware

Computer hardware

1. The CPU

   • Often called the 'brain' of the computer
   • It's main role is to process programs and data
     • does this by repeatedly fetching an instruction from memory and executing it (fetch-execute cycle)
   • CPU components
     • control unit
       • Decides which instruction to carry out next
       • Fetches it from memory
       • Decodes the instruction and executes it
       • Repeats the process (fetch-execute cycle)
     • Arithmetic and Logic Unit (ALU)
       • Carries out arithmetic calculations and performs logical comparisons to assist decision making
         • Logical comparisons = AND,OR,NOT
     • Immediate Access Store (IAS)
       • Stores all programs and data temporarily whilst in use
       • During fetch execute cycle, instructions are fetched from their specific storage location in the IAS using an address
         • Each memory location has a unique address

2. Registers

   • Def- High speed memory locations in the CPU. Have an important role in the fetch execute cycle
   • Program Counter (PC)
     • This stores the address (memory location reference) of the next instruction to be fetched
     • Many program instructions are ordered; the program counter is incremented by 1 each time an instruction is fetched
     • The program counter always points to the next instruction address in the sequence
   • Memory Address Register (MAR)
     • All program instructions are stored in a number of memory locations each of which have a unique address
       • The current instructions address is stored (temporarily) in the MAR
   • Memory Data Register (MDR)
   • Instruction Register (IR)
   • Accumulator