This weekend, HDFC Bank and Axis Bank— two of India's biggest private sector banks—are looking at major system upgrades that will disrupt services for an estimated 140 million customers. HDFC Bank will replace its existing core banking system with a new engineered platform on July 13, serving 93.2 million customers. The exercise will involve a 13.5-hour outage and is carried out to improve customer experience but will restrict several banking services.