1.1 Systems Architecture

1.1 Systems Architecture

1. Von Neumann Architecture

   • Forms the basis of most computer systems
   • Programs and data are stored in the same memory unit

2. Harvard architecture

   • Programs and data are stored in separate memory units

3. FDE cycle

   • Fetch
     • Address from the program counter is copied to the MAR
     • The instruction is fetched from the address in the MAR
     • The instruction is stored in the MDR
     • The program counter points to the next instruction
   • Decode
     • The fetched instruction is decoded by the control unit
   • Execute
     • The decoded instruction is carried out
     • The cycle repeats

4. CPU registers

   • Program counter
     • Holds the memory address of the instruction for each cycle
   • MAR - Memory address register
     • Holds the memory address about to be used by the CPU
   • MDR - Memory Data Register
     • Holds data or instructions that have been fetched from memory
   • Accumulator
     • Stores the results of the calculations done by the ALU

5. CPU - Central processing unit

   • Components
     • CU - Control Unit
       • Controls activities in the CPU
       • Makes FDE cycle happen in order
       • Decodes instrucions
     • ALU - Arithmetic and Logic Unit
       • Performs logical operations
       • Shift operations
       • Arithmetic operations
     • Cache
       • Sits between the CPU and RAM
       • Very fast
       • Holds frequently used data
   • Processes all of the data and instructions to make a computer system work