Question

In a virtual memory system, the I/O operations executed by a user program can be of two different types. Name them and explain when each one of them occurs.

Answer 1

The two types of I/O operations in such a system are the following:

1. Memory Mapped:

In this type, only one group of instructions is used for I/O and memory. The address space is shared. This can slow down the memory addressing capability. It is not considered very efficient due to the same reason. However, it makes it less complex, and the logic of the system becomes very simple as well.

When: It is used when a large group of instructions is to be used. This is useful when performance is in demand. It supports special instructions for various operations.

2. Isolated:

In this type, the I/O uses separate control lines but shares the common bus for address and data with memory. Because both memory and I/O use separate address space, it is called isolated. I/O addresses are called ports. This is considered more efficient. Because of separate buses the size often increases. This also increases complexity.

When: This is used when there is a need for fewer I/O instructions. This is also used when there are small memory requirements. It is also useful for logical and arithmetic operations.