Embedded real-time operating system is the software program that manages all the programs in an embedded device after initial load of programs by a boot loader. Embedded real-time operating system normally guarantees a certain capability within a specified storage size and time constraint as well as with application programs.the most popular rtos are:

LynxOS RTOS

The LynxOS RTOS (real-time operating system) is the higher foundation for real-time systems:An RTOS with Open APIs and Linux ABI compatibility.Perform complex series of tasks within given periods of time and also Support multiple applications with multiple interrupting devices.Take full advantage of today’s powerful high-end microprocessor and advanced networking architecture .All RTOS components within LynxOS are designed for absolute determination i.e.: hard real-time performance. This means that they absolutely must respond within a known or given period of time. This predictable response is ensured even in the presence of heavy Input/Output due to the kernel’s unique threading model, enabling interrupt routines to be extremely short and fast.

QNX RTOS

The QNX RTOS v6.1 has a client-server based architecture. QNX adopts the approach of implementing an OS with a 10 Kilobytes micro-kernelsurrounded by a team of optional processes that provide higher-level OS service .Every process including the device driver has its own virtual memory space. The system can be distributed over several nodes and is network transparent. The system performance is fast and predictable and is robust.It supports Intel x86family of processors, MIPS,strongARM and powerPC
. Documentation is extensive except for the details on the APIs[10]. QNX has successfully been used in tiny ROM-based embedded systems and also in several-hundred node distributed system.

VRTX

VRTX has multitasking facility to solve the real-time performance requirements found in embedded systems. Pre-emptive scheduling is followed ensuring the best response for critical applications. Inter-taskcommunication is by use of mailboxes and queues.VRTX has been designed for development and target system independence as well as real-time clock independence.

Windows CE

Windows CE 3.0 is an Operating system rich in features and is available for a variety of hardware platforms. It exhibits true real-time behavior most of the times.

psos+

pSOS+ is a small kernel suitable for embedded applications. This usesthe software bus to communicate between different modules.