Write the differences between Isolated I/O and Memory Mapped I/O.

Last updated on June 13th, 2020 at 08:31 pm

Memory Mapped I/O and Isolated I/O are two methods of performing input-output operations between CPU and installed peripherals in the system. Memory mapped I/O uses the same address bus to connect both primary memory and memory of hardware devices. Thus the instruction to address a section or portion or segment of RAM can also be used to address a memory location of a hardware device.

On the other hand, isolated I/O uses separate instruction classes to access primary memory and device memory. In this case, I/O devices have separate address space either by separate I/O pin on CPU or by entire separate bus. As it separates general memory addresses with I/O devices, it is called isolated I/O.

Read More: What are memory mapped I/O and isolated I/O?

Differences Between Isolated I/O and Memory Mapped I/O:

Isolated I/O
Memory Mapped I/O
Isolated I/O uses separate memory space.
Memory mapped I/O uses memory from the main memory.
Limited instructions can be used. Those are IN, OUT, INS, OUTS.
Any instruction which references to memory can be used.
The addresses for Isolated I/O devices are called ports.
Memory mapped I/O devices are treated as memory locations on the memory map.
IORC & IOWC signals expands the circuitry.
IORC & IOWC signals has no functions in this case which reduces the circuitry.
Efficient I/O operations due to using separate bus
Inefficient I/O operations due to using single bus for data and addressing
Comparatively larger in size
Smaller in size
Uses complex internal logic
Common internal logic for memory and I/O devices
Slower operations
Faster operations


  1. I studied these in my 7th semester, 1.5 years back. I can't answer you. These are just my notes those I made at that time, hoping that someone else will help you.

  2. difference u writtrn is quite in the easy language ….i love it….plz add some more difference u know…..that may help us

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