SimOS - simulator was developed at Stanford University, USA. The SimOS is a complete machine simulation environment designed for the efficient and accurate study of both single-processor and multiprocessor computer systems. The SimOS simulates computer hardware (CPU, caches, multiprocessor memory buses, disk drives, and other devices) in enough detail to boot and run commercial operating systems, and provides models of the MIPS R4000 and R10000, and Digital Alpha processor families. The SimOS models hardware similar to machines created by Silicon Graphics, Inc. and Digital Equipment Corporation. It is able to save the entire state of the simulated machine to disk and easily restore the simulator to this state at any time. The SimSO was developed using C programming language. Two execution modes are present in the SimOS: direct execution and detailed simulation. Direct execution is user in user space process and detailed simulation entire instruction set is simulated. The MIPS version is somewhat portable and can be built under Irix, So-laris and Linux. It is possible to make some changes in order to get it to compile in some particular environment. The Alpha version can be built under Tru64 Unix. The SimOS present an environment for studying the hardware and software of computer systems. All components needed to run standard operating systems and application programs are available in the SimOS with sufficient level of details. The SimOS provides substantial flexibility in the trade-off between the speed and detail of a simulation. The SimOS' ability to change levels of detail on-the-fly enhances its ability to study complex workloads, allowing the researcher to pay the cost of detailed simulation only when the resulting data is desired [15, 33, 34]. Students, developers, testers, and performance analytics could use the SimOS for studying new computer hardware designs, for analyzing application performance, and for studying operating systems. It has been used on the many projects including the investigation of new architectural designs, the development of the Hive operating system, and for various performance studies of operating systems and applications.