Extending its gains for the fourth day in a row, the Sensex at the Bombay Stock Exchange rose 173 points, or 1 percent, to 17,605 on sustained buying by investors.The Sensex had lost 49 points at the day's low, and added 199 points at the day's high. The Sensex had gained over 560 points in the previous three trading sessions.The Nifty at the National Stock Exchange climbed 56 points, or 1.1 percent, to 5,326. In the broader market, the BSE Midcap index rose 1.3 percent and the Smallcap index added 1.2 percent. Market breadth was positive on the BSE. Turnover on the BSE's cash segment stood at Rs 2,916 crore.All the BSE sectoral indices, except the metal index, ended higher. The Realty index was the leading gainer, surging 2.2%.The Healthcare index rose 1.7%; the Power index, the FMCG index and the Bankex gained 1.4%, each; the Oil and Gas and the PSU indices rose 1.1%, each; the IT index added 0.9%; the Auto and the Tech indices rose 0.7%, each; the Consumer Durables index added 0.4%; and the Capital Goods index gained 0.3%. The Metal index was the only sectoral loser, falling 1.1%.Index heavyweight, Reliance Industries rose 1%.ONGC rose 1.5%, and Bhel gained 1.7%. In pharma counters, Dr Reddy's Labs ended flat. And Sun Pharma rose 2.5% and the stock hit a record high of 558 rupees on Friday.Banking majors rose. ICICI Bank rose 1.2%, SBI gained 1.5%, HDFC Bank added 1.8%.Cement stocks extended yesterday's gains. So Jaiprakash Associates rose 2.7%, ACC rose 1.8%, and hit a 52-week high, Ambuja Cements rose 1.3%, and the stock hit a record high of 173 rupees.Realty stocks extended recent gains. Unitech rose 3% on bargain hunting after slumping 7 per cent on Thursday. Among other realty stocks, HDIL, DLF and Indiabulls Real Estate rose between 0.7% and 1.6%.Auto stocks rose on good vehicle sales in January. Maruti Suzuki India rose 1%, Mahindra & Mahindra rose 1.3% and Tata Motors gained 0.2%.Two wheeler makers declined. So Hero MotoCorp fell 1% and Bajaj Auto fell 0.1%.