Railway technology is the set of machines and software that moves trains safely: the trains themselves, the signals, the automatic braking, the track and the power supply. Indian Railways carries millions of passengers every day, and many Indian cities now have a metro as well. More and more of what keeps these trains moving is software.
Take a metro ride in Bengaluru as the simplest way to see the parts. You tap your card at the gate and board a train. The train is rolling stock, the name for everything that runs on the rails: locomotives, which pull trains, coaches and metro trains. The train moves only when the signalling system allows it. Traditional signalling divides the track into stretches called blocks and allows only one train in a block at a time. Modern metros use communication-based train control (CBTC). In CBTC, each train reports its exact position all the time, so trains can safely run closer together and more trains fit on the same line.
If a driver passes a red signal or goes too fast, automatic train protection applies the brakes by itself. India's own system is called Kavach, and Indian Railways is fitting it on its routes. Under the trains lie the track and the overhead power supply: the rails, the concrete sleepers that hold the rails in place, and the overhead wires that give electric trains their power. Circuit breakers protect that power supply from faults. Sensors and cameras along the track and on the trains feed railway condition monitoring, which predicts when each part will need maintenance, before a failure stops the line.
A main-line railway and a metro are not the same job. Indian Railways runs long-distance, suburban and goods trains on shared tracks, so one section may carry trains of very different speeds and weights. A metro runs only its own identical trains on its own line. That is why a metro can adopt CBTC and driverless trains more easily, while a main-line railway usually upgrades its signals and its protection section by section.
The buyers are railways and metro companies. In India, almost all of them are owned by governments. They buy through government tenders. The systems they buy are rarely replaced and run for decades. Every safety system must pass safety certification before it is used, and the makers keep earning from service after the sale. Condition monitoring is one case of predictive maintenance.