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5 SIMPLE moves to EASILY solve the Rubik's Cube

009. Other high- level languages.

Hundreds of high-level languages have been developed, but only a few have achieved broad acceptance. Fortran [FORmula TRANslator] was developed by IBM corporation between 1954  and 1957 to be used for scientific and engineering applications that require complex mathematical computations. Fortran is still widely used.

COBOL [cOmmon business oriented language] was developed in 1959 by a group of computer manufacturers and government and industrial computer users. COBOL is used primarily for commercial applications that require precise and efficient manipulation of large amounts of data. Today, about half of all business software is still programmed in COBOL. Approximately one million people are actively writing COBOL programs.

Pascal was designed at about the same time as c. It was created by professor nicklaus wirth and was intended for academic use. we say more about pascal in the next section.

Basic was developed in 1965 at Dartmouth university as a simple language to help novices become comfortable with programming. Bill gates implemented Basic on several early personal computers. Today, microsoft- the company bill gates created- is the world's leading software development organization.

008.Java class libraries.

Java programs consits of pieces called classes. classes consits of pieces called methods that perform tasks and return information when they complete their tasks. you can program each piece you may need to form a java program. but most java programmers take advantages of rich collections of existing classes in java class libraries. The class libraries are also known as the java APis[ applications programming interfaces]. Thus there are really two pices to learning the java"world". The first is learning the java language itself so that you can program your own classes and the second is learning how to use the classes in the libraries are provided primarily by compilier vendors. Also , many class libraries are available from the internet and world wide web as shareware[products you can download for a small fee] and freeware[products you can download for free

007. History of java.

Perhaps the microprocessor revolution's most important contribution to date is that it made possible the development of personal computers which may soon number 300 million worldwide. Personal computers have had a profound impact on people and the way organizations conduct and manage their buisness.

Many people believe that the next major area in which microprocessors will have a profound impact is in intelligent consumar eloctronic devices. Recognizing this, sun microsystems funded an internal corporate research project code-named green in 1991. the project resulted in the development of a C and C++ based language which its creator, james gosling, called Oak after an oak tree outside his window at sun. It was later discovered that there already was a computer language called Oak. When a group of sun people visited a local coffee place, the name java was suggested and it stuck.

But the green project ran into some difficulties. The marketplace for intelligent consumar electronic devices was not developing as quickly as sun had anticipated. Worse yet, a major contract for which sun competed was awarded to another company.. So the project was in danger of being cancled. By sheer good fortune, the world wide web exploded in popularity in 1993 and sun people saw the immediate potential of using java to create web pages with so- called dynamic content.

 This breathed new life into the project.

 sun formally announced java at a major conference in may 1995. Ordinarily, an event like this would not have generated much attention. However, java generated immediate interest in the buisness community because of the phenomenal interest in the world wide web. Java is now used to create web pages with dynamic and interactive content, to develop large- scale enterprise applications, to enhance the functionality of world wide web servers[ the computers that provide the content we see in our web browsers], to provide applications for consumar devices[ such as cell phones, pagers and personal ditital assistants], and so on.

006. History of c++.

C++ evolved from C which evolved from two previous language, BCPL and B. BCPL was developed in 1967 by martin Richards as a language for writing operating systems software and compilers. Ken Thompson modeled many features in his language be after their counterparts in BCPL and used b to create early versions of the unix operating system at bell laboratories in 1970 on a digital Equipment corporation PDP-7 computer Both BCPL and be were"typless" language- every data item occupied one"word" in memory. For example it was the programmer's responsibility to treat a data item as a whole number or a real number.

The C language  was evolved from b by  Dennis Ritchie at bell laboratories and was originally Implemented on a DEC PDP-11 computer in 1972. C uses many important  concepts of BCPL  and B while  adding data typing  and other features. C initially became widely known as the development language of the Unix operating system. Today, virtually all new major operating systems are written in C and/orC++. Over the past two decades, c has become available for most computers. C is hardware independent. With careful design, it is possible to write C programs that are portable to most computers.

By the late 1970s, C had evolved into what is now referred to as " traditional C," or " kernighan and ritchie C," The publication by prentice hall in 1978 of kernighn and Ritchie's book, The C programming language, brought wide attention to the language. This publication became one of the most  successful computer science books ever. The widespread use of C with various types of computers[ sometimes called hardware platforms] led to many variations. These were similar,  but often incompatible. This was a serious problem for programmers who needed to  write portable programs that would run on several platforms.. It became clear that a standard version of C was needed. in 1983, the X3j11 technical committee was created under the American national standards committee on computers and information processing[X3] to "provide an unambiguous and machine- independent definition of the language." In 1989, the standard was approved. Ansi cooperated  with the international standard organization[ISO] to  standardize C worldwide; the joint standard document was published in 1990 and is referred to as ANSI/ISO 9899: 1990. The second edition of kernighan and ritchie, published in 1988, reflects this version called ANSI C, a version of the language now used worldwide[Ke88].

C++, an extension of C, was developed by bjarne stroustrup in the early 1980s at bell laboratories. C++ provides a number of features that"spruce up" the C language, but more important, it provides capabilities for object- oriented programming. C++ was recently standardized by the ANSI and ISO committiees.

There is a revolution brewing in the software community. Building software Quickly, correctly and economically remains and clusive goal,  and this at a time when demands for new and more powerful software are soaring. Objects are essentially reusable software components  that model items  in the real world. software developers are discovering that using a modular, object- oriented design and Implementation approach can make software development groups much more productive than is possible with previous popular programming Techniques such as structured programming. Object- oriented programs are often easier to understand, correct and modify.

Many other object- oriented languages have been developed, including smalltalk, developed at Xerox's palo alto research center[PARC].Smalltalk is a pure object- oriented language_ literally everything is an object.C++ is a hybrid language_ it is possible to program in either a C_ like style, an object_ oriented style or both.

005.machine languages, assembly languages and high- level languages.

Programmers write instructions in various programming language, some directly under- stand able by the computer and other that require intermediate translation steps. hundreds of computer languages are in use today. These may be divided into three general types:

1.machine language

2 assembly language

3 high- level language

any computer can directly understand only its own machine language. Machine language is the "natural language" of a particular computer. It is defined by the hardware design of that computer. Machine language generally consist of strings of numbers[ultimately reduced to 1st and 0s] that instruct computers to perform their most elementary operations one at a time. Machine language are machine dependent[i.c,a particular machine language can be used on only one type of computer]. Machine language are cumbersome for humans, as can be seen by the filling section of a machine language  programs that adds overtime pay to base pay and stores the results in gross pay.

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As became computers more popular, it became apparent that machine- language programming was simply too slow and tedious for most programmers. Instead of using the strings of numbers that computers could directly understand, programmers began using English- like abbreviations to represent the elementary operations of the computer. These English- like abbreviations formed the basis of assembly languages. Translator programs called assemblers were developed to convert assembly language programs to machine language at computer speeds. The following section of an assembly- language program also adds overtime pay to base pay and stores the resylt in gross pay, but more clearly than its machine- language equivalent.

Load basepay

Add overpay

Store grosspay

Although such code is clearer to humans, it is incomprehensible to computers until translated to machine language.

Computer usage increased rapidly with the advent of assembly language, but programming in this still required many instructions to accomplish even the simplest tasks. To speed the programming proces, high- level languages were developed in which single statements could be written to accomplish substantial tasks. The translator programs that convert high- level language program into machine language are called compilers. High- level language allow programmers to write instructions that look almost like everyday English and contain commonly used mathematical notation. A paroll program written a high- level language might contain a statement such as;

obviously, high- level language are much  more desirable from the programmer's standpoint than either machine language or assembly language. C, C++ and java are among the most powerful and most widely used high- level programming language. The process of compilling a high- level language program into machine language take  a considerable amount of computer time. Interpreter programs were developed to directly execute high- level language programs without the need for compiling those programs into machine language. Although compiled programs execute much faster than interpreted programs, interpreters are popular in program development invironments in which programs are recomplied frequently as new features are added errors are corrected. Once a program is developed , a compiled version can be produced to run most efficiently.As we study java, you will so that interpreters have played an especiacally important part in helping java achive its goal of portability across a great vareity of platforms.

004. personal, distributed and client/server computing.

In 1977, apple computer popularized the phenomenon of personal computing. Initially, was a hobbyist's dream. computers became economical enough for people to buy them for their own personal use In 1981, IBM, the world's largests computer vendor, introduced the IBM personal computer. Almost overnight, personal computing became legitimate in business, industry and goverment organizations.

But this computers were"stand-alone" units_ people did their work on their own machines and then transported disks back and forth to share information. Although early personals computers were not powerful enough to timeshare several users, these machines could be linked together in computer networks, sometimes over telephone lines and sometimes in local area networks[LANs] within an organization. This led to the phenomenon of distributed computing, in which an organization's computing, instead of being performed strictly at some central computer installation, is distributed over networks to the sites at which the real work of the organization is performed. Personal computer were powerful enough to handle the computing requirements of individual users, and to handle the basic communications tasks of passing information back and forth electronically.

Today's most powerful personal computers are as powerful as the million dollar machines of just a decade ago. The most powerful desktop machines- called workstations provide individual users with enormous capabilities. Information is easily shared across computer networks were some computers called file servers offer a common store of programs and data that may be used by client computers distributed throughtout the network hence the term client/ server computing. c and c++ have became the programming language of choice for writing software for operating systems, for computer networking and for distributed client/server applications. Java is rapidly becoming the language of choice for developing internet- based applications; many programmers have discovered that programming in jaba helps them be more productive then programming in c or c++. Today's popular operating systems such as unix, linux, os/2. macOs, windows and windows Nt provide the kinds of capabilities discussed in this section

003.Evolution of operating systems.

Early computers were capable of performing only one job or task at a time. This form of computer operation is often called single-user batch processing. The computer runs a single program at a time while processing data in groups or batches. In this early systems, users generally submitted their jobs to the computer center on decks on punched cards. users often had to wait hours or even days before printouts were returned to their desks.

Software systems called operating systems were developed to help make it more convenient to use computers.Early operating systems managed the smooth transition between jobs. This minimized the time it took for computer operators to switch between jobs, and hence increased the amount of work, or throughput,computers could process.

As computers became more powerful, it became evident that single-user batch processing rarely utilized the computer's resources efficiently. Instead, it was throught that many jobs or tasks could be made to share the resources of the computer to achieve better utilization. This is called multiprogramming involves the "simultaneous" operation of many jobs on the computer_the computer shares its resources among the jobs competing for its attention. With early multiprogramming operating system, users still submitted jobson decks of punched cards and waited hours or days for results.

In the 1960s, several groups in industry and the universities pioncered itmesharing operating systems. Timesharing is a special case of multiprogramming in which users access the computer through terminals, typically devices with keyboards and screens. In a typical timesharing  computer system, there may be dozens or even hundreds of users sharing the computer at once.The computer does not actually run all the users' jobs simultancously.Rather, it runs a small portion of one user's job and then moves on to service the next user.The computer does this so quickly that it may provide service to each user several times per second. Thus the users' programs appear to be running simultaneously.An advantage of timesharing is that the user receives almost immediate responses to requests rather than having to wait long periods for results as with previous modes of computing . Also if a particular user is currently idle, the computer can continue to service other users rather than wait for one user.