I know the Linux Windows2000 XP UNIX Mach. I have used Linus Windows and XP.

Linux is a modern free operating system based on UNIX standards. It has been designed to run efficiently and reliably on common PC hardware; it also runs on a variety of other platforms. It provides a programming interface and user interface compatible with standard UNIX systems and can run a large number of UNIX applications including an increasing number of commercially supported applications.

Microsoft designed Windows XP to be an extensible portable operating system. Windows XP supports multiple operating environments and symmetric multiprocessing including both 32-bit and 64-bit processors and NUMA computers. The use of kernel objects to provide basic services along with support for client-server computing enables Windows XP to support a wide variety of application environments.

Windows has a 32 bit operating system with multiple boot functions that can coexist with other operating systems. Preemptive multitasking and multi thread operation are realized. SMP (symmetric multiprocessing) technology is used to support multi CPU systems. It supports CISC (such as Intel systems) and RISC (such as Power PC R4400 etc.) a variety of hardware platforms.

It also is interoperable with a variety of network operating systems.