The Compuer Level Hierarchy

• Divide and Conquer
• Look at the system as a series of layers
  • User Level, executable programs, ...
  • High Level Language, C++, Java, COBOL
  • Assembly Language, Intel, Sparc, gnu
  • System Software, OS, libraries
  • Machine Language, X86, Sparc, HP-PA (ISA)
  • Control, microcode or hardwired
  • Digital Logic, gates and circuits.

The Von Neumann Model

• On early machines, programming was equivelent to moving wires
• Turn the machine on, wire your program, run your program, turn the machine off
• Mauchly and Eckert decided to use the concept of a stored program
  • Put the program in memory with the data
  • But they couldn't write a paper on this (Secret government research project)
  • So John Von Neumann did
• Stored program or Von Neumann Architecture
  • CPU, ALU, Registers, Memory, I/O system
  • Ability to carry out sequential instruction processing
  • A single path from main memory to the CPU, alternating fetches between the data and instruction.
• 
• And employs the fetch execute cycle
  • Fetch the instruction at the address stored in the program counter into the instruction register
  • Increment the PC
  • Decode the instruction
  • Fetch the operands based on the instruction
  • Execute the instruction
  • Possibly place results of instruction in memory
• An extension is the bus model
  • 
• This model has a built in bottleneck getting information from memory to the CPU

Non-Von Neumann Models

• Multiple approaches
• Parallel computing (multiple cpus, multiple memories, ...)
• MIMD, SIMD, ...
• Amdahl's Law - each program has a sequential part and a parallel part and the sequential part will limit the speedup