Abstraction layer

In the Unix operating system, most types of input and output operations are considered to be streams of bytes being read from a by the operating system which presents an abstract interface which allows the programmer to read and write bytes from/to the device. The operating system then performs the actual transformation needed to read and write the stream of bytes to the device.

Most graphics libraries such as OpenGL provide an abstract graphical device model as an interface. The library is responsible for translating the commands provided by the programmer In computer science, an abstraction level is a generalization of a model or algorithm, away from any specific implementation. These generalizations arise from broad similarities that are best encapsulated by models that express similarities present in various specific implementations. The simplification provided by a good abstraction layer allows for easy reuse by distilling a useful concept or metaphor so that situations where it may be accurately applied can be quickly recognized.

A good abstraction will generalize that which can be made abstract; while allowing specificity where the abstraction breaks down and its successful application requires customization to each unique requirement or problem.

Frequently abstraction layers can be composed into a hierarchy of abstraction levels. The ISO-OSI networking model comprises seven abstraction layers. Each layer of the OSI ISO networking model encapsulates and addresses a different part of the needs of much digital communications thereby reducing the complexity of the associated engineering solutions.

A famous aphorism of Butler Lampson goes: All problems in computer science can be solved by another level of indirection; this is often deliberately mis-quoted with "abstraction" substituted for "indirection". Kevlin Henney's corollary to this is, "...except for the problem of too many layers of indirection."

Computer architecture

A typical vision of a computer architecture as a series of abstraction layers: hardware, firmware, assembler, kernel, operating system and applications (see also Tanenbaum 79).

In computer architecture, a computer system is usually represented as consisting of five abstraction levels: hardware, firmware, assembler, operating system and processes (Tanenbaum 79).

Bibliography

• Tanenbaum, Andrew S. (1979). Structured Computer Organization. Englewood Cliffs, New Jersey: Prentice-Hall. ISBN 0-13-148521-0.