Building further on its initial strong gains, the Sensex at the Bombay stock Exchange had surged a massive 637 points, or 3.2 percent, to 20,600 in afternoon trade, a short while ago. Earlier in the morning, the Sensex had shot up a huge 574 points, or 2.9 per cent, to 20,536, on strong buying interest by funds and retail investors, triggered by a strengthening rupee and firm global bourses, after the US Federal Reserve decided to keep its monetary stimulus programme intact. The 30-share Sensex had gained nearly 230 points in the previous three trading sessions. Markets rallied across the globe, after the US Federal Reserve very unexpectedly decided not to start tapering its monthly 85-billion dollar bond buying program just yet. So stock indices in Japan, China, Hong Kong and Singapore had climbed between 0.3 percent and 1.8 percent, today. Key European markets in the UK, Germany and France had also posted good gains of between 1 percent and 1.3 percent. And the US Dow Jones Industrial Average had jumped 1 per cent to hit a record high in yesterday's trade