| # Zircon and LK |
| |
| Zircon was born as a branch of [LK](https://github.com/littlekernel/lk) and even |
| now many inner constructs are based on LK while the layers above are new. For |
| example, Zircon has the concept of a process but LK does not. However, a Zircon |
| process is made of LK-level constructs such as LK's ``thread_t``. |
| |
| LK is a Kernel designed for small systems typically used in embedded |
| applications. It is a good alternative to commercial offerings like |
| [FreeRTOS](http://www.freertos.org/) or [ThreadX](http://rtos.com/products/threadx/). |
| Such systems often have a very limited amount of ram, a fixed set of peripherals |
| and a bounded set of tasks. |
| |
| On the other hand, Zircon targets modern phones and modern personal computers |
| with fast processors, non-trivial amounts of ram with arbitrary peripherals |
| doing open ended computation. |
| |
| More specifically, some the visible differences are: |
| |
| + LK can run in 32-bit systems. Zircon is 64-bit only. |
| + Zircon has first class user-mode support. LK does not. |
| + Zircon has a capability-based security model. In LK all code is trusted. |
| |
| Over time, even the low level constructs have changed to accommodate the new |
| requirements and to better fit the rest of the system. |
| |
