Memory-Mapped I/O (see Fig. 7)

Figure 7: a) Separate I/O and memory space. b) Memory-mapped I/O. c) Hybrid.

• Separate I/O and memory space
  • I/O controller registers appear as I/O ports
  • Accessed with special I/O instructions
• Memory-mapped I/O
  • Controller registers appear as memory
  • Use normal load/store instructions to access
• Hybrid; x86 has both ports and memory mapped I/O
• Bus Architectures (see Fig. 8)

  Figure 8: a) A single-bus architecture. b) A dual-bus memory architecture.

  
  • A single-bus architecture; if the computer has a single bus, having everyone look at every address is straightforward
  • A dual-bus memory architecture; the trend in modern personal computers is to have a dedicated high-speed memory bus. This bus is tailored for optimize memory performance, with no compromises for the sake of slow I/O devices. Pentium systems even have three external buses (memory, PCI, ISA)