1.1 Systems architecture

1.1 Systems architecture

1. Purpose of the CPU

   • Fetch Decode Execute INSTRUCTIONS
     • 1] The processor checks the program counter to see which instruction to run next
       • 2] The program counter gives an address value in the memory of where the next instruction is.
         • 3] The processor fetches the instruction value from this memory location.
           • 4] Once the instruction has been fetched, it needs to be decoded and executed. For example, this could involve taking one value, putting it into the ALU, then taking a different value from a register and adding the two together.
             • 5] Once this is complete, the processor goes back to the program counter to find the next instruction.
               • 6] This cycle is repeated until the program ends

2. Registers

   • MAR
     • Memory Address Register
       • Stores the memory location of the next piece of data to be fetched from / transferred to memory
   • MDR
     • Memory Data Register
       • Temporarily stores the data that is being fetched from / transferred to memory
   • PC
     • Program Counter
       • Holds the address of the next instruction to be executed
   • ACC
     • Accumulator
       • Stores the results of any calculations performed by the ALU. Keeps a running total

3. CPU Components

   • ALU
     • Arithmetic Logic Unit
       • Where data is processed and manipulated. Performs arithmetic and logic operations
   • CU
     • Control Unit
       • Controls the flow of data inside and outside the CPU
   • Cache
     • used to temporarily hold instructions and data that the CPU is likely to reuse

4. Von Neumann

   • Von Neumann architecture is based on the stored-program computer concept, where instruction data and program data are stored in the same memory

5. CPU Performance

   • clock speed
     • The number of FDE cycles per second. 4GHz = CPU can do 4 billion FDE cycles per second.
   • cache size
     • Cache stores commonly used instructions. CPU can access instructions from cache faster than from the RAM
     • The bigger the cache is ... the more frequent instructions can be stored there
   • No. of cores
     • Quad Core = 4 CPUs ... The more cores means the more instructions can be processed at the same time

6. Embedded Systems

   • A simplified computer system within a system
     • Microwave
     • Dishwasher
     • Smart TV

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