Saturday, February 10, 2007

Beginer's All-purpose Symbolic Instruction Code

In computer programming, BASIC an acronym for Beginner's All-purpose Symbolic Instruction Code refers to a family of high-level programming languages. It was originally designed in 1963, by John George Kemeny and Thomas Eugene Kurtz at Dartmouth College, to provide access for non-science students to computers. At the time, nearly all computer use required writing custom software, which was something only scientists and mathematicians tended to do. The language became widespread on home microcomputers in the 1980s, and remains popular to this day.

Prior to the mid-1960s, computers were extremely expensive tools used only for special-purpose tasks. A simple batch processing arrangement ran only a single "job" at a time, one after another. During the 1960s, however, faster and more affordable computers became available. With this extra processing power, computers would sometimes sit idle, without jobs to run.

Programming languages in the batch programming era tended to be designed, like the machines on which they ran, for specific purposes (such as scientific formula calculations or business data processing or eventually for text editing). Since even the newer less expensive machines were still major investments, there was strong tendency to consider efficiency to be the most important feature of a language. In general, these specialized languages were difficult to use and had widely disparate syntax.

As prices decreased, the possibility of sharing computer access began to move from research labs to commercial use. Newer computer systems supported time-sharing, a system which allows multiple users or processes to use the CPU and memory. In such a system the operating system alternates between running processes, giving each one running time on the CPU before switching to another. The machines had become fast enough that most users could feel they had the machine all to themselves. In theory, timesharing reduced the cost of computing tremendously, as a single machine could be shared among (up to) hundreds of users.

The original BASIC language was designed in 1963 by John Kemeny and Thomas Kurtz and implemented by a team of Dartmouth students under their direction. BASIC was designed to allow students to write programs for the Dartmouth Time-Sharing System. It intended to address the complexity issues of older languages with a new language design specifically for the new class of users time-sharing systems allowed — that is, a less technical user who did not have the mathematical background of the more traditional users and was not interested in acquiring it. Being able to use a computer to support teaching and research was quite attractive enough. In the following years, as other dialects of BASIC appeared, Kemeny and Kurtz' original BASIC dialect became known as Dartmouth BASIC.

The eight design principles of BASIC were:

1. Be easy for beginners to use.
2. Be a general-purpose programming language.
3. Allow advanced features to be added for experts (while keeping the language simple for beginners).
4. Be interactive.
5. Provide clear and friendly error messages.
6. Respond quickly for small programs.
7. Not require an understanding of computer hardware.
8. Shield the user from the operating system.

The language was based partly on FORTRAN II and partly on ALGOL 60, with additions to make it suitable for timesharing. It had been preceded by other teaching-language experiments at Dartmouth such as the DARSIMCO (1956) and DOPE (1962 implementations of SAP and DART (1963) which was a simplified FORTRAN II). Initially, BASIC concentrated on supporting straightforward mathematical work, with matrix arithmetic support from its initial implementation as a batch language and full string functionality being added by 1965. BASIC was first implemented on the GE-265 mainframe which supported multiple terminals. Contrary to popular belief, it was a compiled language at the time of its introduction. It was also quite efficient, beating FORTRAN II and ALGOL 60 implementations on the 265 at several fairly computationally intensive programming problems such as maximization Simpson's Rule.

The designers of the language decided to make the compiler available without charge so that the language would become widespread. They also made it available to high schools in the Dartmouth area and put a considerable amount of effort into promoting the language. As a result, knowledge of BASIC became relatively widespread (for a computer language) and BASIC was implemented by a number of manufacturers, becoming fairly popular on newer minicomputers like the DEC PDP series and the Data General Nova. The BASIC language was also central to the HP Time-Shared BASIC system in the late 1960s and early 1970s. In these instances the language tended to be implemented as an interpreter, instead of (or in addition to) a compiler.

Several years after its release, highly-respected computer professionals, notably Edsger W. Dijkstra, expressed their opinions that the use of GOTO statements, which existed in many languages including BASIC, promoted poor programming practices.[2] Some have also derided BASIC as too slow (most interpreted versions are slower than equivalent compiled versions) or too simple (many versions, especially for small computers left out important features and capabilities).

Notwithstanding the language's use on several minicomputers, it was the introduction of the MITS Altair 8800 microcomputer in 1975 that provided BASIC a path to universality. Most programming languages required more memory (and/or disk space) than were available on the small computers most users could afford. With the slow memory access that tapes provided and the lack of suitable text editors, a language like BASIC which could satisfy these constraints was attractive. BASIC also had the advantage that it was fairly well known to the young designers who took an interest in microcomputers. Kemeny and Kurtz's earlier proselytizing paid off in this respect. One of the first to appear for the 8080 machines like the Altair was Tiny BASIC, a simple BASIC implementation originally written by Dr. Li-Chen Wang, and then ported onto the Altair by Dennis Allison at the request of Bob Albrecht (who later founded Dr. Dobb's Journal). The Tiny BASIC design and the full source code were published in 1976 in DDJ.

In 1975, MITS released Altair BASIC, developed by Bill Gates and Paul Allen as Micro-Soft. The first Altair version was co-written by Gates, Allen and Monte Davidoff. Versions of Microsoft BASIC soon started appearing on other platforms under license, and millions of copies and variants were soon in use; it became one of the standard languages on the Apple II (based on the quite different 6502 MPU). By 1979, Microsoft was talking with several microcomputer vendors, including IBM, about licensing a BASIC interpreter for their computers. A version was included in the IBM PC ROM chips and PCs without floppy disks automatically booted into BASIC just like many other small computers.

Newer companies attempted to follow the successes of MITS, IMSAI, North Star and Apple, thus creating a home computer industry; meanwhile, BASIC became a standard feature of all but a very few home computers. Most came with a BASIC interpreter in ROM, thus avoiding the unavailable, or too expensive, disk problem. Soon there were many millions of machines running BASIC variants around the world, likely a far greater number than all the users of all other languages put together.

There are more dialects of BASIC than there are of any other programming language. Most of the home computers of the 1980s had a ROM-resident BASIC interpreter.

The BBC published BBC BASIC, developed for them by Acorn Computers Ltd, incorporating many extra structuring keywords, as well as comprehensive and versatile direct access to the operating system. It also featured a fully integrated assembler. BBC BASIC was a very well-regarded dialect, and made the transition from the original BBC Micro computer to more than 30 other platforms.

During this growth time for BASIC, many magazines were published such as Creative Magazine that included complete source codes for games, utilities, and other programs. Given BASIC's straightforward nature, it was considered a simple matter to type in the code from the magazine and execute the program. Different magazines were published featuring programs for specific computers, though some BASIC programs were universal and could be input into any BASIC-using machine.

Many newer BASIC versions were created during this period. Microsoft sold several versions of BASIC for MS-DOS/PC-DOS including BASICA, GW-BASIC (a BASICA-compatible version that did not need IBM's ROM) and QuickBASIC. Turbo Pascal-publisher Borland published Turbo BASIC 1.0 in 1985 (successor versions are still being marketed by the original author under the name PowerBASIC).

These languages introduced many extensions to the original home computer BASIC, such as improved string manipulation and graphics support, access to the file system and additional data types. More important were the facilities for structured programming, including additional control structures and proper subroutines supporting local variables.

However, by the latter half of the 1980s newer computers were far more capable with more resources. At the same time, computers had progressed from a hobbyist interest to tools used primarily for applications written by others, and programming became less important for most users. BASIC started to recede in importance, though numerous versions remained available. Compiled BASIC or CBASIC is still used in many IBM 4690 OS point of sale systems.

BASIC's fortunes reversed once again with the introduction of Visual Basic by Microsoft. It is somewhat difficult to consider this language to be BASIC, because of the major shift in its orientation towards an object-oriented and event-driven perspective. While this could be considered an evolution of the language, few of the distinctive features of early Dartmouth BASIC, such as line numbers and the INPUT keyword, remain.

Many BASIC dialects have also sprung up in the last few years, including Bywater BASIC and True BASIC (the direct successor to Dartmouth BASIC from a company controlled by Kurtz). Recently, the remaining community using Microsoft's pre-Visual Basic products have begun to switch wholesale to FreeBASIC, a GPLed compiler which has been in the process of moving BASIC onto a GCC backend. Many other BASIC variants and adaptations have been written by hobbyists, equipment developers, and others, as it is a relatively simple language to develop translators for. An example of an open source interpreter, written in C, is MiniBasic.

The ubiquity of BASIC interpreters on personal computers was such that textbooks once included simple TRY IT IN BASIC exercises that encouraged students to experiment with mathematical and computational concepts on classroom or home computers.

Sample Code
10 INPUT "What is your name: "; U$
20 PRINT "Hello "; U$
30 REM
40 INPUT "How many stars do you want: "; N
50 S$ = ""
60 FOR I = 1 TO N
70 S$ = S$ + "*"
100 REM
110 INPUT "Do you want more stars? "; A$
120 IF LEN(A$) = 0 THEN GOTO 110
130 A$ = LEFT$(A$, 1)
140 IF (A$ = "Y") OR (A$ = "y") THEN GOTO 40
150 PRINT "Goodbye ";
160 FOR I = 1 TO 200
170 PRINT U$; " ";
180 NEXT I

No comments: