Algol

Algol , famous variable star in the constellation Perseus ; Bayer designation β Persei; 1992 position R.A. 3 ^h 07.7 ^m , Dec. +40°55′. Algol's variation in apparent magnitude , from 2.06 to 3.28, is due to the fact that it is an eclipsing binary star , with one component revolving about the other with a period of 2 days, 20 hr, 49 min. Because the plane of revolution is almost parallel to the line of sight, the star dims noticeably when the dimmer component passes in front of, or eclipses, the brighter component, and dims again very slightly when the brighter component eclipses the dimmer one (see eclipse ); the primary minimum, when the brighter component is eclipsed, lasts about 10 hr. Algol is of spectral class B8 V and is about 105 light-years from the earth. The name Algol comes from the Arabic Ras al Ghul, which means "demon's head," and the star is sometimes called the Demon Star.

Algol Acronym for algorithmic language. The generic name for a family of high-level languages of great significance in the development of computing. In 1958 the Association for Computing Machinery (ACM) in the US and the Gessellschaft für Angewante Mathematik und Mechanik (GAMM) in Europe set up a joint committee to define an international algorithmic language (IAL). The language that was designed became known as Algol, and was later called Algol 58 to distinguish it from later versions. Algol 58 was not intended to be a viable language, and in 1960 an augmented committee was convened to devise the second iteration, which was published as the language Algol 60. See also JOVIAL.

Algol 60 was much more popular in Europe than in the US, probably due to the dominance of IBM and Fortran in the North American market. It introduced many new concepts, notably block structure (see block-structured languages), nested scopes, modes of parameter passing to procedures, and the definition of the language introduced the now classic BNF notation for describing syntax. The influence of Algol 60 can be seen in all succeeding languages, and it stands as a milestone in the development of programming languages.

In the years following the publication of the Algol 60 Report, a working group of the International Federation for Information Processing was set up to consider the definition of a successor to Algol 60. There were many dissensions within the group, and eventually a minority report was issued proposing the language Algol 68. The first implementation of Algol 68, named ALGOL 68R, was produced at the Royal Signals and Radar Establishment in the UK. ALGOL 68R demonstrated that Algol 68 was a viable language (not at the time a self-evident proposition).

Although Algol 68 introduced many novel concepts of great theoretical interest and significance, its practical application was almost nil. One of the most notable features of Algol 68 is its formal specification using a two-level grammar. Although a very precise definition, it is very difficult to understand, and this difficulty partly accounts for the low acceptance of the language. One of the most significant effects of the split in the Algol 68 working group is that it led indirectly to the development of Pascal.