What is the difference between hard and soft real-time systems?

Timing constraints. Both types systems must accomplish tasks within given timing deadline. Hard RT systems cannot tolerate missed deadlines, they are designed to complete critical tasks within specified time limits, the main objective is reliabilty (flight control, missile guidance, medical equipment, manufacturing automation, etc.). Soft RT systems prioritize tasks and can occasionally miss the deadline, it is note desired but tolerable, the prime objective is performance (multimedia streaming, gaming, VR, etc.).

In hard real-time systems, meeting strict and deterministic timing constraints is crucial. Failure to meet deadlines can have severe consequences, possibly leading to system failure or safety issues. Examples: Aerospace systems, medical devices, and automotive safety systems. Soft real-time systems also have timing constraints, but they are less strict compared to hard real-time systems. Missing occasional deadlines may lead to a decrease in system performance but typically does not result in catastrophic failure. Examples: Multimedia applications, online streaming, and some gaming systems can be considered soft real-time, as they aim for timely responses but allow some flexibility in meeting deadlines.

Hard realtime systems can be expensive in the initial product development stages. Once have volume demand then the bulk buy effect takes into account and drops the prices during mass production. However with the chip shortage this again affects the final cost due to chip availability from manufacturers. But once the hard realtime product is completed then there might be also a few hardware revisions to go through, keeping the price high when compared to soft realtime systems with readily available CoTs parts and an Application that can just easily be downloaded and updated. Hardware is hard but that is the challenge since the world is an analog hands on place

It depends on the application, but where timing is the most critical metric then a hard realtime system implementation is needed. The most accurate time sources are from hardware based atomic clocks, HPTR modules, GPS Time with a PPS syncing signal ( assuming a clear LOS to the satellites). These feed the Soft realtime sources such as NTP servers where the availability of the service depends on domestic connectivity.

To learn more about implementing hard hard realtime systems focus more on the timing accuracy and how to manage the timing drift error. I believe this is the main issue of all realtime systems. How to maintain the same timing over the the platform, device, machine, globe.. because in the end the data acquired has a time stamp next to it. Tips and tricks to manage this timing results in either good data into the system. Remember garbage in = garbage out. And cleaning out of time data can be quite challenging not to mention the data becomes tainted. Learn about ASIC, SoC, FPGA ( VHDL), system clocks, RTC, GPS PPS to implement. Some applications: SONAR, LIDAR, Phased Array ( radar (FoD,Anti drone)/ communications (starlink) )

In my experience most implementations of hard realtime systems are bare metal with the emphasis on timing, code stability and full deterministic behaviour. Examples of such Hard realtime systems are Data acquisition systems such as Sonar, Lidar, Phased Array Antennas - their data processing is done on hardware like ASICs, SOCs & FPGAs. Why? Because the all their calculations are time sensitive due to Time of Flight signal characteristics. Soft realtime happens on Mobile phone Applications where the data transactions happen in the cloud on the application servers. Bank applications transactions happen in realtime & time stamped but there is still a chance of data loss due to connectivity issues. Where hard realtime does not have this issue.