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http://chandrakantha.com/articles/indian_music/santur.html sez:
Santur is an instrument indigenous to Kashmir, but nowadays played throughout the North. It is a hammered dulcimer which is struck with light wooden mallets. The number of strings may be as few as 24 or more than 100. Typical sizes tend to be around 80. It has a vibrant tone and has become very popular in the last 20 years.
One must not confuse the Indian santur with the Persian santur. The Indian santur is box-like while the Persian version is much wider.