CPU

CPU

1. Central Processing Unit

   • chip that does all of the calculations
   • three mayor parts
     • Control Unit (CU)
       • acts as
         • organizing force
       • does not execute instructions
       • controls sequence of execution
       • controls what is stored in the cache
       • takes care of fetching and decoding
       • works with special registers
         • Instruction Register (IR)
           • holds instruction currently being executed
         • Program Counter (PC)
           • contains address of the next instruction to be executed
         • Memory Data Register (MDR)
           • contains the data to be stored in the computer storage, or the data after a fetch from the computer storage
           • Connected to data bus
           • data can go both ways
             • to and from memory
           • can load its data from
             • Data bus
               • reading data
             • CPU registers
               • storing data
         • Memory Address Register (MAR)
           • stores memory address from which data will be fetched, sent or stored
           • holds memory location of data that needs to be accessed
           • enable communication between the memory and processing unit
       • uses buses to transfer information to the ALU and the CPU
     • Arithmetic and Logic Unit (ALU)
       • performs
         • arithmetic operations
           • adding
           • dividing
           • substracting
           • multiplying
         • logical operations
           • AND
           • OR
           • NOT
     • Primary memory
       • cache
         • frequently used instructions are stored here
       • connects with ALU and CU

2. uses buses to transfer information

   • address
     • addresses of locations in the primary memory are transferred
     • transferred with data bus
   • data
     • contains
       • information
       • instructions
   • connected to each other by a collection of wires

3. MACHINE CYCLE

   • 1) Fetch
     • involves retrieving an instruction from memory
   • 2) Decode
     • instructions is broken up into parts
       • CU
   • 3) execute
     • execute is performed
   • 4) writeback
     • outputs the result to some form of memory
       • ALU

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