The technique of assigning a memory address to each I/O device in the computer system is called -

Question

Prepp Team · Accepted Answer

Understanding I/O Device Addressing

In a computer system, the Central Processing Unit (CPU) needs to communicate with input/output (I/O) devices such as keyboards, screens, disks, etc. To do this, each I/O device, or specific registers within it (like data or control registers), must be identifiable and accessible by the CPU. This identification is done by assigning a unique address to each device or register. The method used for assigning these addresses and allowing the CPU to access them is crucial for system design and performance.

Memory-Mapped I/O Explained

The technique described in the question, where each I/O device is assigned a memory address, is known as Memory-mapped I/O (MMIO).

In Memory-mapped I/O:

I/O devices and system memory share the same address space.
The CPU uses the same instructions to access both memory locations and I/O device registers. For example, instructions like LOAD and STORE (or their equivalents) are used for both reading from/writing to memory and reading from/writing to I/O devices.
The hardware is designed such that when the CPU generates an address, the bus control logic determines whether the address corresponds to a memory location or an I/O device.
This approach simplifies the CPU's instruction set architecture because no dedicated I/O instructions are needed.

Comparison with Ported I/O (I/O-Mapped I/O)

Memory-mapped I/O is often contrasted with Ported I/O, also known as I/O-Mapped I/O or Isolated I/O.

In Ported I/O:

I/O devices have a separate address space from memory.
The CPU requires special I/O instructions (e.g., IN, OUT) to access I/O device registers.
These instructions typically have a dedicated I/O address bus or use control signals to indicate that the address on the address bus is for an I/O port, not memory.

Here's a simple comparison:

Feature	Memory-Mapped I/O	Ported I/O
Address Space	Shared with memory	Separate from memory
CPU Instructions	Standard memory access instructions (e.g., LOAD, STORE)	Special I/O instructions (e.g., IN, OUT)
Address Bus	Single address bus used for both memory and I/O	Often uses the same address bus but with separate control signals or a dedicated I/O address bus
Instruction Set Complexity	Simpler (fewer instruction types)	More complex (dedicated I/O instructions)

Analyzing the Options

Let's consider the provided options in the context of assigning memory addresses to I/O devices:

Ported I/O: As discussed, Ported I/O uses a separate address space and special I/O instructions, not the memory address space. So, this option is incorrect.
Dedicated I/O: This term is not a standard computer architecture term for an I/O addressing technique. It might vaguely imply I/O is handled separately, but it doesn't precisely describe the method of assigning memory addresses.
Memory-mapped I/O: This technique precisely matches the description of assigning a memory address to each I/O device, allowing access using standard memory instructions. This is the correct answer.
Wired I/O: This term refers more to the physical connection or implementation details of I/O circuitry (e.g., hardwired logic) rather than the logical method of assigning addresses for CPU access. It is not an addressing technique.

Therefore, the technique of assigning a memory address to each I/O device in the computer system is correctly identified as Memory-mapped I/O.

Revision Table: Key I/O Addressing Concepts

Term	Description	Relevance to Question
Memory-mapped I/O	I/O devices share the memory address space; accessed with memory instructions.	Matches the technique described.
Ported I/O (I/O-Mapped I/O)	I/O devices have a separate address space; accessed with special I/O instructions.	Contrasts with the technique described.
Address Space	The range of addresses available to the CPU for accessing memory and/or I/O.	Fundamental concept in I/O addressing.
CPU Instructions	Commands executed by the CPU to perform operations like reading/writing data.	Different addressing techniques use different instruction types.

Additional Information on Computer Architecture & I/O

Understanding how a CPU interacts with I/O devices is fundamental to computer architecture. The choice between Memory-mapped I/O and Ported I/O affects the design of the CPU, the bus interface, and the device controllers.

Memory-mapped I/O is often preferred in modern processors because it allows the use of a richer set of memory-access instructions, potentially including those for data manipulation (though manipulation is typically done on data moved to CPU registers). It also simplifies the bus interface logic. However, it consumes part of the memory address space.
Ported I/O allows for a full memory address space, as I/O addresses are separate. It might be simpler to implement device decoding if I/O addresses are few. However, it requires dedicated I/O instructions and potentially separate control signals on the bus.
Many architectures, like x86, support both Memory-mapped I/O and Ported I/O. Others, like ARM, primarily use Memory-mapped I/O.

The address assigned to an I/O device allows the CPU to target specific registers within that device. These registers control the device's operation (control registers), hold data being transferred (data registers), or provide status information (status registers).