ISOLATED I/O
MEMORY MAPPED I/O
Different address spaces for memory and I/O devicesSame address bus to address memory and I/O devicesAll address can be used by the memory because have different address space for memory and I/O device.Address space shared with I/O devices so addressable memory become less for memory.Uses a special class of CPU
instructions to access I/O devices.
Access to the I/O devices using regular instructionsIn this I/O address are called ports.Normal memory address are for bothMore efficient due to separate busesLesser efficientLarger in size due to more busesSmaller in sizeIt is complex due to separate logic is used to control both.Simpler logic is used as I/O is also treated as memory only.x86 Intel microprocessors – IN and OUT instructionsIt is most widely used I/O method
"Isolated" ? As a denomination for non-memory-mapped I/O ?
- Memory-mapped I/O is I/O that's accessed through the (single) data or unified memory bus. (Whether data or unified memory bus depends on the architecture.)
- Contrasting to the above, non-memory-mapped I/O has got its own "I/O bus" (which might or might not share physical data and address lines with the "normal" data bus, but has at least 1 control line to indicate that a bus access is meant to access I/O and not data. And yes - to access a separate I/O bus, additional instructions are required.
Intel processors were known for the separate I/O bus. (Not sure whether current Intel CPUs still implement that.) The advantage is that you can easily implement different timings for I/O and memory accesses. And, considering systems with data caches, the differentiation between cacheable data and non cacheable I/O is easy as well. But it seems the non-memory-mapped I/O is a race on the way to extinction...
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