Think of it like a club with a max capacity of 10 people, where some people have VIP cards. If a person with a VIP card wants to get into the club, the bouncer will kick out one of the people inside that doesn’t have a VIP card to make space for them.

For a more technical explanation:

There are several processors on computers and each can be in use by 1 process at a time. Different processes can get different amounts of time based on their priority (called niceness in Linux) and they’ll be removed from the processor once their time is up until their next share of time.

On a real-time kernel some processes are marked as real-time (certain range of niceness values, can’t remember the exact range). If a process that is real-time says it needs some processor time, a process that isn’t real-time that’s currently running will be immediately ripped off the processor to make room for the real-time process.

I guess i am still skipping on how real time kernel address the pause? it just never pauses or it no longer needs to be paused?

When hardware has data ready for a program it generates an interrupt that lets the OS know that there is data ready for an application. My understanding is that real-time OSs give high priority to interrupts so that they’re processed quickly - usually within a fixed period of time (e.g. they may have a max time between interrupt and processing).

as a side note, is this similar technology they use in high precision manufacturing?

In those cases it may be more likely they use a micro-controller that doesn’t run any OS at all - at least not a multi-tasking one. If you’re just running a single program you don’t need to worry about latency due to other applications running.