Hyderabad was historically known as a pearl and diamond trading centre, and it continues to be known as the City of Pearls. Many of the city's traditional bazaars, including Laad Bazaar, Begum Bazaar and Sultan Bazaar, have remained open for centuries. However, industrialisation throughout the 20th century attracted major Indian manufacturing, research and financial institutions, including Bharat Heavy Electricals Limited, the National Geophysical Research Institute and the Centre for Cellular and Molecular Biology. Special economic zones dedicated to information technology have encouraged companies from across India and around the world to set up operations and the emergence of pharmaceutical and biotechnology industries in the 1990s led to the area's naming as India's "Genome Valley". With an output of US$74 billion, Hyderabad is the fifth-largest contributor to India's overall gross domestic product.