Systems Programming and Portability

Operating systems are the best examples of programs that need to be aware of hardware's specifications and limitations, and to successfully hide as much of this detail from potential applications through good software engineering practices.

If the operating system, itself, has any chance of being ported to different architectures, its own implementation must identify and isolate its hardware dependencies.

Unix, the historic forefather of Linux and macOS (and many others), was the first portable operating system, reimplemented in C to support its migration from early Digital Equipment Corp (DEC). minicomputers. C itself was invented specifically for the purpose of enabling Unix to be portable.

We here at Bell Laboratories were truly dumfounded when this visitor from an unknown school in Australia reported his elegant procedure. Doug McIlroy, Head Unix Research Group, Bell Laboratories

• UNIX: a portable operating system? [Miller, 1978].
• Unix portability: underutilized in embedded development [Crooks, 2002].
• The First Port of UNIX [Reinfelds, 1978].

Today, of course, we see Linux ported to nearly every form of contemporary architecture because:

• hardware-dependent code has been identified and isolated,

• software abstractions and application-programming interfaces hide hardware characteristics from applications, and

• successful applications do not introduce, or depend upon, any hardware dependencies.