Explain the Direct Memory Access and interrupt driven I/O techniques. How are these two techniques different to each other? Also, explain different kinds of Interrupts

Both Direct Memory Access (DMA) and interrupt-driven I/O are techniques used in computer systems to facilitate data transfer between I/O devices and memory, but they operate in different ways and have different characteristics.

Direct Memory Access (DMA):

Definition: Direct Memory Access (DMA) is a technique where a specialized DMA controller transfers data directly between memory and I/O devices without CPU intervention.

How it Works:

1. The CPU sets up the DMA transfer by providing the DMA controller with the necessary parameters, such as the starting memory address, the direction of transfer (read or write), and the number of bytes to transfer.
2. The CPU then initiates the transfer by issuing a command to the DMA controller.
3. The DMA controller takes over control of the system bus and transfers data directly between the I/O device and memory without involving the CPU.
4. Once the transfer is complete, the DMA controller notifies the CPU via an interrupt, and the CPU resumes control of the system.

Key Characteristics:

• DMA reduces CPU overhead by offloading data transfer tasks from the CPU.
• DMA is particularly useful for large data transfers, such as those involving disk drives or network interfaces, as it improves system performance.
• DMA requires additional hardware in the form of a DMA controller.

Interrupt-Driven I/O:

Definition: Interrupt-driven I/O is a technique where the CPU initiates a data transfer with an I/O device and then continues executing other tasks. When the device has completed the transfer, it generates an interrupt to notify the CPU.

How it Works:

1. The CPU initiates a data transfer with the I/O device by sending commands or data.
2. The CPU continues executing other tasks while waiting for the transfer to complete.
3. When the device has completed the transfer, it generates an interrupt signal to the CPU.
4. The CPU responds to the interrupt, retrieves the data from the device, and continues execution.

Key Characteristics:

• Interrupt-driven I/O allows the CPU to perform other tasks while waiting for data transfer to complete, improving overall system efficiency.
• Interrupt-driven I/O is suitable for devices that require immediate attention or for small, occasional data transfers.
• The CPU handles interrupt processing, which can introduce some overhead and affect system performance.

Differences between DMA and Interrupt-Driven I/O:

1. Control: In DMA, a specialized DMA controller takes over control of the system bus and handles the data transfer independently, whereas in interrupt-driven I/O, the CPU remains in control and handles interrupt processing.
2. CPU Involvement: DMA offloads data transfer tasks from the CPU entirely, while interrupt-driven I/O requires CPU involvement for initiating and handling data transfer.
3. Suitability: DMA is more suitable for large, continuous data transfers, while interrupt-driven I/O is suitable for small, occasional data transfers or devices that require immediate attention.

Different Kinds of Interrupts:

1. Hardware Interrupts: These are generated by external hardware devices to signal the CPU that they require attention. Examples include keyboard interrupts, mouse interrupts, and timer interrupts.
2. Software Interrupts: These are generated by the CPU itself or by software instructions to request specific services from the operating system, such as system calls or interrupt-driven I/O operations.
3. Maskable Interrupts: These interrupts can be temporarily disabled or masked by the CPU using the interrupt mask register. They can be enabled or disabled based on the program’s needs.
4. Non-Maskable Interrupts (NMI): These interrupts cannot be masked by the CPU and require immediate attention. They are typically used for critical system events, such as power failure or hardware faults.