Bare-Metal (Super-Loop)
The firmware runs directly on the hardware, without an operating system — typically as an endless loop with interrupts. Advantage: minimal overhead, lowest memory and power consumption, full control. Disadvantage: as the range of functions grows, managing concurrency, timing and states within the loop quickly becomes unwieldy.
RTOS (Real-Time Operating System)
A lightweight operating system takes over the scheduling of multiple tasks, their synchronisation and the communication between them. Its strength is deterministic scheduling: predictable, fast response times to events — the prerequisite for genuine real-time requirements. The price: more memory, context-switching overhead and greater complexity.
Determinism is the core
The difference from an ordinary OS lies in the response time: an RTOS responds deterministically within guaranteed bounds, a general-purpose OS does not. Where deadlines are hard (engine control, safety functions), that is exactly what counts.
And Embedded Linux?
For compute-intensive tasks, connectivity and complex stacks, Embedded Linux comes into play — more functionality, but considerably more resources and, as a rule, no hard real-time without additional measures.
Rule of thumb
Simple, resource-constrained devices without real multitasking: bare-metal. Several time-critical tasks that must be cleanly coordinated: RTOS. Networked, data-intensive systems: Embedded Linux. We make this choice per project — not out of habit.