Computer, Program, Programming language, Programming language theory ----wikipedia

A computer is a programmable machine that receives input, stores and manipulates data//information, and provides output in a useful format.

While a computer can, in theory, be made out of almost anything (see misconceptions section), and mechanical examples of computers have existed through much of recorded human history, the first electronic computers were developed in the mid-20th century (1940–1945). Originally, they were the size of a large room, consuming as much power as several hundred modern personal computers (PCs).[1] Modern computers based on integrated circuits are millions to billions of times more capable than the early machines, and occupy a fraction of the space.[2] Simple computers are small enough to fit into mobile devices, and can be powered by a small battery. Personal computers in their various forms are icons of the Information Age and are what most people think of as "computers". However, the embedded computers found in many devices from MP3 players to fighter aircraft and from toys to industrial robots are the most numerous.

 

A computer program (also a software program, or just a program) is a sequence of instructions written to perform a specified task for a computer.[1] A computer requires programs to function, typically executing the program's instructions in a central processor.[2] The program has an executable form that the computer can use directly to execute the instructions. The same program in its human-readable source code form, from which executable programs are derived (e.g., compiled), enables a programmer to study and develop its algorithms.

Computer source code is often written by computer programmers. Source code is written in a programming language that usually follows one of two main paradigms: imperative or declarative programming. Source code may be converted into an executable file (sometimes called an executable program or a binary) by a compiler and later executed by a central processing unit. Alternatively, computer programs may be executed with the aid of an interpreter, or may be embedded directly into hardware.

Computer programs may be categorized along functional lines: system software and application software. Two or more computer programs may run simultaneously on a single computer, a process known as multitasking.

 

A programming language is an artificial language designed to express computations that can be performed by a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine, to express algorithms precisely, or as a mode of human communication.

Many programming languages have some form of written specification of their syntax (form) and semantics (meaning). Some languages are defined by a specification document. For example, the C programming language is specified by an ISO Standard. Other languages, such as Perl, have a dominant implementation that is used as a reference.

The earliest programming languages predate the invention of the computer, and were used to direct the behavior of machines such as Jacquard looms and player pianos. Thousands of different programming languages have been created, mainly in the computer field, with many more being created every year. Most programming languages describe computation in an imperative style, i.e., as a sequence of commands, although some languages, such as those that support functional programming or logic programming, use alternative forms of description.

 

Programming language theory (commonly known as PLT) is a branch of computer science that deals with the design, implementation, analysis, characterization, and classification of programming languages and their individual features. It falls within the discipline of computer science, both depending on and affecting mathematics, software engineering and linguistics. It is a well-recognized branch of computer science, and an active research area, with results published in numerous journals dedicated to PLT, as well as in general computer science and engineering publications. Most undergraduate computer science programs require coursework in the topic.

 

Computer software, or just software, is the collection of computer programs and related data that provide the instructions telling a computer what to do. The term was coined to contrast to the old term hardware (meaning physical devices). In contrast to hardware, software is intangible, meaning it "cannot be touched".[1] Software is also sometimes used in a more narrow sense, meaning application software only. Sometimes the term includes data that has not traditionally been associated with computers, such as film, tapes and records.[2]

一般来讲软件被划分为系统软件、应用软件,其中系统软件包括操作系统和支撑软件（微软近期又发布嵌入式系统，即硬件级的软件，是电脑及其它设备运算速度更快更节能）

　　软件的真正含义

　　程序设计的最终结果是软件。

 

软件是用户与硬件之间的接口界面。用户主要是通过软件与计算机进行交流。软件是计算机系统设计的重要依据。为了方便用户，为了使计算机系统具有较高的总体效用，在设计计算机系统时，必须全局考虑软件与硬件的结合，以及用户的要求和软件的要求。

　　1.运行时，能够提供所要求功能和性能的指令或计算机程序集合。

　　2.程序能够满意地处理信息的数据结构。

　　3.描述程序功能需求以及程序如何操作和使用所要求的文档。