5.8 Processors

• Overview of a "computer". Three major sections, the processor, Input and Output, and Memory. These are interconnected with signals that fall into three different groups.
  1. DATA. The actual data values are transfered on this bus.
  2. ADDRESS. The address of the of where the data is comming to or from is transfered on this bus. This bus has on some systems been combined with the data bus. The most common width today is 32 bits. This allows for 4,294,967,296 addresses.
  3. CONTROL. This is a collection of signals that indicates what is happening. Read or write. Memory or I/O. Bit, byte, word, (Size of transfer). Interrupts. DMA (Dirrect Memory Access) Type of data, instruction (code) or data.
• Internal Registers
  • PC or Program counter. IP or Instruction Pointer. This points to where in memory the next instruction will come from.
  • Instruction Register. Where the instruction is placed after it is fetched from memory. This may not be a real register at all. It will not be accessable by te user in most cases.
  • Address registers. Registers that point to memory locations.
  • Numeric registers. Registers that take on numeric values for computation. These may be used for floating point numbers on some systems.
  • General Purpose Registers. Used for logical instructions and integer arithmetic.
• Memory Operations. An address is provided to the memory subssytem and a value can be stored or retreived from the location. The value could be a bit, byte, 16 bits, 32 bits, 64 bits, or other size.
• Fetch Execute Cycle This is an ideal way of looking at a processor. That the processor gets one instruction from memory, updates the instruction pointer, then executes the instruction. Once this has been done it does it again. Over and over and over. Reality is far more complicated than this.
• Pipe-line operation The overlap of instruction fetch and execute. The overlap of multiple instructions at the same time. Executing multiple instructions at the same time. Branch prediction.
• Input and Output operations - I/O operations
• Instruction Sets. What computers can "do". Very fast, but not "really" very complicated.
  • Arithmetic and logic instructions.
  • Move instructions (to & from - memory, registers and I/O - bits, bytes, words(various sizes),
  • Simple decisions. Is X > than Y?
• RISC CISC - trade offs
• different architectures von Newman & Harvard