IO ports and IO memory

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IO Space and memory space
Speaking of this problem, it involves hardware knowledge, X86 system, with two address space: IO Space and memory space, and RISC instruction system CPU (such as ARM, PowerPC, etc.) usually only achieve a physical address space, that is, memory space.
Memory Space: Memory address range, 32-bit operating system memory space of 2 of the 32 power, that is, 4G.
IO space: A X86-specific space, a separate address space from the memory space, and a 32-bit X86 with 64K io space.
IO port: When register or memory is in IO space, it is called IO port. General registers are also commonly known as I/O ports, or I/Os ports, this I/O port can be mapped in memory space, can also be mapped in I/O space.
IO Memory: When the register or memory is in memory space, called IO memory