What is buffer? What are buffered reads and writes?

I heard the word buffer after a long time today and wondering if somebody can give a good overview of buffer and some开发者_StackOverflow examples of how it matters in today's world.

A buffer is generally a portion of memory that contains data that has not yet been fully committed to its intended device. In the case of buffered I/O, generally there is a fast device and a slow device. The devices themselves need not have disparate speeds, but perhaps the interfaces between them differ or perhaps it is more time-consuming to either produce or consume the data than the other part is.

The idea is that you temporarily store the generated data in a buffer so that it is not lost when the slower device isn't ready to handle it. Once the device is ready, the another buffer may take the current buffer's place and the consuming device will process the data in the first buffer.

In this manner, the slower device receives the data at a moderated pace rather than the fire-hose that the original data source can be.