Editing Mach (kernel) (section)

===Unix pipes===
A key concept in the original Unix operating system is the idea of a [[pipeline (Unix)|pipe]]. A pipe is an [[abstraction (computer science)|abstraction]] allowing data to be moved as an unstructured stream of bytes between programs. Using pipes, users can link together multiple programs to complete tasks, feeding data through several consecutive small programs. This contrasts with typical operating systems of the era, which require a single large program that can handle the entire task, or alternately, used files to pass data, which was resource-expensive and time-consuming.{{Citation needed|date=February 2025}}

Pipes were built on the underlying [[input/output]] system. This system is, in turn, based on a model where drivers are expected to periodically "block" while they wait for tasks to complete. For instance, a [[printer driver]] might send a line of text to a [[line printer]] and then have nothing to do until the printer completes printing that line. In this case, the driver indicates that it was blocked, and the operating system allows some other program to run until the printer indicates it is ready for more data. In the pipes system the limited resource was memory, and when one program filled the memory assigned to the pipe, it would naturally block. Normally this would cause the consuming program to run, emptying the pipe again. In contrast to a file, where the entire file has to be read or written before the next program can use it, pipes made the movement of data across multiple programs occur in a piecemeal fashion without any programmer intervention.{{Citation needed|date=February 2025}}

However, implementing pipes in memory buffers forced data to be copied from program to program, a time-consuming and resource intensive operation. This made the pipe concept unsuitable for tasks where quick turnaround or low latency was needed, such as in most [[device driver]]s. The operating system's kernel and most core functionality was instead written in a single large program. When new functionality, such as [[computer network]]ing, was added to the operating system, the size and complexity of the kernel grew, too.{{Citation needed|date=February 2025}}