Operating Windows 2000 Professional and Windows XP
Although they share a common user interface, use similar file naming conventions, and come from the same manufacturer, Windows 2000 and Windows XP are radically different operating system environments from Windows 9x. Some of the key differences are Windows 2000 and Windows XP's ability to provide symmetric multiprocessing (SMP) support, allowing the computer system to use more than one processor at the same time; Windows 2000 and Windows XP's ability to operate applications written both to the Win32 and the Portable Operating System Interface for UNIX (POSIX) environment; the NT File System (NTFS) that can be used by Windows 2000 and Windows XP to support the security features not found in Windows 9x; and Windows advanced networking controls.
The Windows 2000 and Windows XP operating systems can be broken down into two components: the kernel mode and user mode, each of which contains several subsystems that can be visualized as a series of layers.