PS/2 keyboards use an interrupt-based system. When you press a key, the keyboard sends a hardware interrupt signal to the CPU, demanding immediate attention. This makes PS/2 theoretically faster and more responsive, which is why some hardcore competitive gamers still prefer them. It also allows for "Full N-Key Rollover," meaning you can press every single key on the keyboard simultaneously, and the computer will register all of them.
Unlike USB keyboards, true PS/2 keyboards are not typically hot-swappable. If you unplug a PS/2 keyboard while the PC is on, the computer may not recognize it when you plug it back in until you perform a full reboot. Key Differences Between HID and PS/2