The magnitude of Muslim attrocities in India is so great that I grossly understimate their scope simply by attempting to describe them. By the sword of Islam, an entire civilization was destroyed and the number of dead easily number in the millions over several decades. The value of the booty--'jewels and unbored pearls and rubies, shining like sparks or like wine congealed with ice, and emeralds like fresh sprigs of myrtle, and diamonds in size and weight like pomegranates' [Smith Oxford History of India p207]--can never be measured. As a result of [this] fanaticism, thousands of temples which had represented the art of India through a millennium were laid in ruins.
We can never know, from looking at India today, what grandeur and beauty she once possessed. [Will Durant] This rich cultural heritage, like the foundations and materials of Hindu temples used to erect Muslim mosques, were highjacked by Islam. Indian mathemeticians conceived algebra and the number zero, which were translated to the Muslim world through its conquests, and then brought to the West through conquest; Islamic civilization now mistakenly recieves credit for these innovations. India before Islam was one of the most advanced civilizations of all time.
According to Prof. K.S. Lal, the author of the Growth of Muslim population in India, the Hindu population decreased by about 80 million between 1000 AD, the year Mahmud Ghazni invaded India and 1525 AD, a year before the battle of Panipat.
One can safely add another 20 million Hindus to this list to account for the number that were killed during the Mughal rule or the rule of the Muslim rulers in the Deccan plateau. By all known accounts of world history, as pointed out by Koenard Elst in his book the Negationism in India, destruction of about 100 million hindus is perhaps the biggest holocaust in the whole world history.
http://www.hinduwebsite.com/history/holocaust.asp