PRS is one of the least visible and most consequential pieces of Indian public digital infrastructure, and it predates almost all of it. Introduced in 1986, it computerised a service used daily by millions long before the internet was a factor, and CONCERT then did something conceptually similar to what interoperable payment rails did decades later - it made location irrelevant, so a passenger in one city could book a train running between two others. The 2002 move to internet booking and the 2014 Next Generation e-Ticketing upgrade each responded to a step change in demand. The current modernisation responds to a third. What makes it interesting is that the constraint has shifted from total volume to peak concurrency: the system handles enormous daily throughput adequately and fails at the tatkal moment, which is a different engineering problem requiring resilience and queue management rather than simply more capacity. For exam purposes this backgrounder is unusually useful because it lays out a clean, dated milestone sequence, and dated sequences are what factual questions are built from.