The Sensex, is the key benchmark index of the Bombay Stock Exchange (BSE), and is also known as the BSE index or 30-share price index. The BSE is one of the oldest stock exchange in India, which was formed way back in the year 1875. The BSE has over 5,000 companies listed on the exchange, out of which daily trading is witnessed in over 2,000 companies. The Sensex is free-float market-weighted (or market capitalisation) stock market index of 30-prominent business houses, varied among different sectors, in India. Initially, the Sensex or the BSE index, was calculated on the basis of fixed market-weightage. Reliance, Infosys, ICICI Bank, HDFC Bank and Tata Steel are some of the prominent companies (also known as stocks), which are part of the Sensex-30. The base year for calculating the Sensex was 1979. In July 1990, the BSE index for the first ever-time crossed the four-digit mark (1,000+mark). Similarly in the February 2006, the Sensex crossed the five-digit mark, and went on to scale past 20,000-mark in December 2007. The Sensex was re-christened as S&P Sensex in February 2013, after the BSE tied-up with Standard and Poor's to use the latter's brand. Recently, on December 9, 2013, the BSE index recorded a fresh all-time high of 21,484. Strong company fundamentals, robust economic growth and fund flows are few of the key factors that drive the markets in India.