A hard real-time system (also known as an immediate real-time system) is
hardware or software that must operate within the confines of a stringent
deadline.
The application may be considered to have failed if it does not
complete its function within the allotted time span.
The chief design goal is not high throughput, but rather a guarantee of a soft or
hard performance category.
An RTOS that can usually or generally meet a
deadline is a soft real-time OS, but if it can meet a deadline deterministically it
is a hard real-time OS
Hard time real operating system example – defence systems like missiles
Soft time real operating system example- audio and video systems