Architecture (562409), страница 14
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In the mid-1980s IBM collaborated with Microsoft to develop an operating system called OS/2 to replace the aging MS-DOS. OS/2 ran older applications written for MS-DOS and newer, OS/2-specific applications that could run concurrently with each other in a process called multitasking. IBM and Microsoft released the first version of OS/2 in 1987. In 1991 Microsoft and IBM ended their collaboration on OS/2. IBM released several new versions of the operating system throughout the 1990s, while Microsoft developed its Windows operating systems.
In the late 1980s IBM was the world’s largest producer of a full line of computers and a leading producer of office equipment, including typewriters and photocopiers. The company was also the largest manufacturer of integrated circuits. The sale of mainframe computers and related software and peripherals accounted for nearly half of IBM’s business and about 70 to 80 percent of its profits.
| V | RECENT DEVELOPMENTS |
In the early 1990s, amid a recession in the U.S. economy, IBM reorganized itself into autonomous business units more closely aligned to the company’s markets. The company suffered record losses in 1992 and, for the first time in its history, IBM cut stock dividends (to less than half of their previous value). John F. Akers, chairman of IBM since 1985, resigned in early 1993. Louis V. Gerstner, Jr., was named chairman of the company later that year. In 1995, IBM paid $3.5 billion to acquire Lotus Development Corporation, a software company, expanding its presence in the software industry. Beginning in 1996, IBM began increasing its stock dividends as the company returned to profitability. In 1997 an IBM supercomputer known as Deep Blue defeated world chess champion Garry Kasparov in a six-game chess match. The victory was hailed as a milestone in the development of artificial intelligence.
In 1998 IBM built the world’s fastest supercomputer for the Department of Energy at the Lawrence Livermore National Laboratory. The computer is capable of 3.9 trillion calculations per second, and was developed to simulate nuclear-weapons tests. In 1999 IBM announced a $16-billion, seven-year agreement to provide Dell Computer Corporation with storage, networking, and display peripherals–the largest agreement of its kind ever. IBM also announced plans to develop products and provide support for Linux, a free version of the UNIX operating system.
Programming Language
| I | INTRODUCTION |
Programming Language, in computer science, artificial language used to write a sequence of instructions (a computer program) that can be run by a computer. Similar to natural languages, such as English, programming languages have a vocabulary, grammar, and syntax. However, natural languages are not suited for programming computers because they are ambiguous, meaning that their vocabulary and grammatical structure may be interpreted in multiple ways. The languages used to program computers must have simple logical structures, and the rules for their grammar, spelling, and punctuation must be precise.
Application of Programming Languages
Programming languages allow people to communicate with computers. Once a job has been identified, the programmer must translate, or code, it into a list of instructions that the computer will understand. A computer program for a given task may be written in several different languages. Depending on the task, a programmer will generally pick the language that will involve the least complicated program. It may also be important to the programmer to pick a language that is flexible and widely compatible if the program will have a range of applications. The examples shown here are programs written to average a list of numbers. Both C and BASIC are commonly used programming languages. The machine interpretation shows how a computer would process and execute the commands from the programs.
Programming languages vary greatly in their sophistication and in their degree of versatility. Some programming languages are written to address a particular kind of computing problem or for use on a particular model of computer system. For instance, programming languages such as Fortran and COBOL were written to solve certain general types of programming problems—Fortran for scientific applications, and COBOL for business applications. Although these languages were designed to address specific categories of computer problems, they are highly portable, meaning that they may be used to program many types of computers. Other languages, such as machine languages, are designed to be used by one specific model of computer system, or even by one specific computer in certain research applications. The most commonly used programming languages are highly portable and can be used to effectively solve diverse types of computing problems. Languages like C, PASCAL, and BASIC fall into this category.
| II | LANGUAGE TYPES |
Programming languages can be classified as either low-level languages or high-level languages. Low-level programming languages, or machine languages, are the most basic type of programming languages and can be understood directly by a computer. Machine languages differ depending on the manufacturer and model of computer. High-level languages are programming languages that must first be translated into a machine language before they can be understood and processed by a computer. Examples of high-level languages are C, C++, PASCAL, and Fortran. Assembly languages are intermediate languages that are very close to machine language and do not have the level of linguistic sophistication exhibited by other high-level languages, but must still be translated into machine language.
| A | Machine Languages |
In machine languages, instructions are written as sequences of 1s and 0s, called bits, that a computer can understand directly. An instruction in machine language generally tells the computer four things: (1) where to find one or two numbers or simple pieces of data in the main computer memory (Random Access Memory, or RAM), (2) a simple operation to perform, such as adding the two numbers together, (3) where in the main memory to put the result of this simple operation, and (4) where to find the next instruction to perform. While all executable programs are eventually read by the computer in machine language, they are not all programmed in machine language. It is extremely difficult to program directly in machine language because the instructions are sequences of 1s and 0s. A typical instruction in a machine language might read 10010 1100 1011 and mean add the contents of storage register A to the contents of storage register B.
| B | High-Level Languages |
High-level languages are relatively sophisticated sets of statements utilizing words and syntax from human language. They are more similar to normal human languages than assembly or machine languages and are therefore easier to use for writing complicated programs. These programming languages allow larger and more complicated programs to be developed faster. However, high-level languages must be translated into machine language by another program called a compiler before a computer can understand them. For this reason, programs written in a high-level language may take longer to execute and use up more memory than programs written in an assembly language.
| C | Assembly Language |
Computer programmers use assembly languages to make machine-language programs easier to write. In an assembly language, each statement corresponds roughly to one machine language instruction. An assembly language statement is composed with the aid of easy to remember commands. The command to add the contents of the storage register A to the contents of storage register B might be written ADD B,A in a typical assembly language statement. Assembly languages share certain features with machine languages. For instance, it is possible to manipulate specific bits in both assembly and machine languages. Programmers use assembly languages when it is important to minimize the time it takes to run a program, because the translation from assembly language to machine language is relatively simple. Assembly languages are also used when some part of the computer has to be controlled directly, such as individual dots on a monitor or the flow of individual characters to a printer.
| III | CLASSIFICATION OF HIGH-LEVEL LANGUAGES |
High-level languages are commonly classified as procedure-oriented, functional, object-oriented, or logic languages. The most common high-level languages today are procedure-oriented languages. In these languages, one or more related blocks of statements that perform some complete function are grouped together into a program module, or procedure, and given a name such as “procedure A.” If the same sequence of operations is needed elsewhere in the program, a simple statement can be used to refer back to the procedure. In essence, a procedure is just a mini-program. A large program can be constructed by grouping together procedures that perform different tasks. Procedural languages allow programs to be shorter and easier for the computer to read, but they require the programmer to design each procedure to be general enough to be used in different situations.
Functional languages treat procedures like mathematical functions and allow them to be processed like any other data in a program. This allows a much higher and more rigorous level of program construction. Functional languages also allow variables—symbols for data that can be specified and changed by the user as the program is running—to be given values only once. This simplifies programming by reducing the need to be concerned with the exact order of statement execution, since a variable does not have to be redeclared, or restated, each time it is used in a program statement. Many of the ideas from functional languages have become key parts of many modern procedural languages.
Object-oriented languages are outgrowths of functional languages. In object-oriented languages, the code used to write the program and the data processed by the program are grouped together into units called objects. Objects are further grouped into classes, which define the attributes objects must have. A simple example of a class is the class Book. Objects within this class might be Novel and Short Story. Objects also have certain functions associated with them, called methods. The computer accesses an object through the use of one of the object’s methods. The method performs some action to the data in the object and returns this value to the computer. Classes of objects can also be further grouped into hierarchies, in which objects of one class can inherit methods from another class. The structure provided in object-oriented languages makes them very useful for complicated programming tasks.
Logic languages use logic as their mathematical base. A logic program consists of sets of facts and if-then rules, which specify how one set of facts may be deduced from others, for example:
If the statement X is true, then the statement Y is false.
In the execution of such a program, an input statement can be logically deduced from other statements in the program. Many artificial intelligence programs are written in such languages.
| IV | LANGUAGE STRUCTURE AND COMPONENTS |
Programming languages use specific types of statements, or instructions, to provide functional structure to the program. A statement in a program is a basic sentence that expresses a simple idea—its purpose is to give the computer a basic instruction. Statements define the types of data allowed, how data are to be manipulated, and the ways that procedures and functions work. Programmers use statements to manipulate common components of programming languages, such as variables and macros (mini-programs within a program).
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