uC-OS uC-OS-II and uC-OS-III Features Comparison
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The table below shows the evolution of µC/OS over the years, comparing the features available in each version.
Table - 1-1 µC/OS, µC/OS-II and µC/OS-III Features Comparison Chart
| Feature | µC/OS | µC/OS-II | >µC/OS-III |
|---|---|---|---|
| Year introduced | 1992 | 1998 | 2009 |
| Book | Yes | Yes | Yes |
| Source code available | Yes | Yes | Yes |
| Preemptive Multitasking | Yes | Yes | Yes |
| Maximum number of tasks | 64 | 255 | Unlimited |
| Number of tasks at each priority level | 1 | 1 | Unlimited |
| Round Robin Scheduling | No | No | Yes |
| Semaphores | Yes | Yes | Yes |
| Mutual Exclusion Semaphores | No | Yes | Yes (Nestable) |
| Event Flags | No | Yes | Yes |
| Message Mailboxes | Yes | Yes | No (not needed) |
| Message Queues | Yes | Yes | Yes |
| Fixed Sized Memory Management | No | Yes | Yes |
| Signal a task without requiring a semaphore | No | No | Yes |
| Option to Post/Signal without scheduling | No | No | Yes |
| Send messages to a task without requiring a message queue | No | No | Yes |
| Software Timers | No | Yes | Yes |
| Task suspend/resume | No | Yes | Yes (Nestable) |
| Deadlock prevention | Yes | Yes | Yes |
| Scalable | Yes | Yes | Yes |
| Code Footprint | 3K to 8K | 6K to 26K | 6K to 24K |
| Data Footprint | 1K+ | 1K+ | 1K+ |
| ROMable | Yes | Yes | Yes |
| Run-time configurable | No | No | Yes |
| Compile-time configurable | Yes | Yes | Yes |
| ASCII names for each kernel object | No | Yes | Yes |
| Pend (i.e. Wait) on multiple objects | No | Yes | Yes |
| Task registers | No | Yes | Yes |
| Built-in Kernel Awareness support | No | Yes | Yes |
| Built-in performance measurements | No | Limited | Extensive |
| Built-in trace points | No | No | Yes |
| User definable hook functions | No | Yes | Yes |
| Time stamps on posts | No | No | Yes |
| Optimizable Scheduler in assembly language | No | No | Yes |
| Catch a task that returns | No | No | Yes |
| Tick handling at task level | No | Yes | Yes |
| Source code available | Yes | Yes | Yes |
| Number of services | ~20 | ~90 | ~75 |
| MISRA-C:1998 | No | Yes | N/A |
| MISRA-C:2012 | No | No | Yes |
| DO178B Level A and EUROCAE ED-12B | No | Yes | Yes |
| Medical FDA pre-market notification (510(k)) and pre-market approval (PMA) | No | Yes | Yes |
| Medical IEC-62304 | No | Yes | Yes |
| SIL3 IEC for transportation and nuclear systems | No | Yes | Yes |
| IEC-61508 | No | Yes | Yes |