The table below shows the evolution of µC/OS over the years, comparing the features available in each version.
| Feature | µC/OS | µC/OS-II | µC>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 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 on multiple objects | No | Yes | Yes |
| Task registers | No | Yes | Yes |
| Built-in performance measurements | No | Limited | Extensive |
| User definable hook functions | No | Yes | Yes |
| Time stamps on posts | No | No | Yes |
| Built-in Kernel Awareness support | No | Yes | Yes |
| Optimizable Scheduler in assembly language | No | No | Yes |
| Catch a task that returns | No | No | Yes |
| Tick handling at task level | No | No | Yes |
| Source code available | Yes | Yes | Yes |
| Number of services | ~20 | ~90 | ~70 |
| MISRA-C:1998 | No | Yes (except 10 rules) | N/A |
| MISRA-C:2004 | No | No | Yes (except 7 rules) |
| DO178B Level A and EUROCAE ED-12B | No | Yes | In progress |
| Medical FDA pre-market notification (510(k)) and pre-market approval (PMA) | No | Yes | In progress |
| SIL3/SIL4 IEC for transportation and nuclear systems | No | Yes | In progress |
| IEC-61508 | No | Yes | In progress |
Table 1-1 µC/OS, µC/OS-II and µC/OS-III Features Comparison Chart