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1 vote
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Of the following, which best characterizes computers that use memory-mapped $I/O$?

  1. The computer provides special instructions for manipulating $I/O$ ports
  2. $I/O$ ports are placed at addresses on the bus and are accessed just like other memory locations
  3. To perform $I/O$ operations. it is sufficient to place the data in an address register and call channel to perform the operation
  4. $I/O$ can be performed only when memory management hardware is turned on
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2 Answers

6 votes
6 votes
In memory some of the address of the Memory are assigned to IO port. so whenever those address are placed we refer to the IO devices.

option B
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  1. can u explain why C is wrong
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2 votes
2 votes
→ Memory-mapped I/O uses the same address space to address both memory and I/O devices.
→ The memory and registers of the I/O devices are mapped to (associated with) address values.
→ So when an address is accessed by the CPU, it may refer to a portion of physical RAM, or it can instead refer to the memory of the I/O device. Thus, the CPU instructions used to access the memory can also be used for accessing devices.
→ Each I/O device monitors the CPU's address bus and responds to any CPU access of an address assigned to that device, connecting the data bus to the desired device's hardware register.
→ To accommodate the I/O devices, areas of the addresses used by the CPU must be reserved for I/O and must not be available for normal physical memory.
→ The reservation may be permanent, or temporary (as achieved via bank switching).

Correct option - (b)
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