I/O Buffering

I/O Buffering

In device management, buffers are used when I/O devices exchange data with the processor to reduce the mismatch between CPU and device speeds, increase parallel operation, and reduce interrupt frequency.

Buffering structures include:

Single Buffer

For input, a channel first sends data to a buffer, and the CPU takes it for processing. The channel then supplies more data, repeating until input completes. Output works in the opposite direction. Because the buffer is a mutually exclusive region, single buffering cannot let the CPU and channel access the same buffer simultaneously, limiting the improvement in CPU/device parallelism.

Double Buffer

Two buffers are used alternately. The CPU and channel can access different buffers: while the CPU accesses one, the channel accesses the other. Double buffering can be used in real systems, but systems have many peripherals, and two buffers may still struggle to match device and processor speeds. Modern systems generally use multiple buffers or buffer pools.

Multiple Buffers

Multiple buffers are connected into two groups, one dedicated to input and the other to output. They are often organized as circular queues, also called circular buffers.

Buffer Pool

Multiple buffers are connected and managed together in a structure that can serve both input and output.