The Architecture of Microsoft XP and Linux

There are four basic types of user mode processes in XP, the first is system support processes (not service processes) such as logon, or Winlogon, and the session manager. The second is service processes that are started by service control manager e.g.- host Win32 services such as Task Scheduler. The third is user applications such as DOS, Windows 3.1 and Win32. And finally environment subsystem that emulates other operating systems, for example Windows XP only supports the Win32 environment. Applications pass operating system service requests through dynamic link libraries. A DLL is a set of functions or data that interface between user applications and operating system.

A conventional operating system usually segregates virtual memory into kernel space and user space. Kernel space is only reserved for running the kernel, kernel extensions and some devices drivers. In most operating systems the kernel memory is never swapped out to disk. User space is the memory area where all user mode applications work and this memory can be swapped out when necessary. Shown below is a simplified diagram of the Windows XP Architecture.

Kernel components of Windows XP are Executive, kernel, device drivers, hardware abstraction layer and windowing and graphics. Executive provides basic operating system services such as memory management and security. Kernel provides low-level operating system functions such as thread scheduling. Device drivers translate input/output requests to hard input/output requests. The hardware abstraction layer insulates the kernels/drivers. The windowing and graphics implements the user interface such as Windowing interface or graphical user interface (GUI).

The architecture for Linux is given in the simplified diagram below. The system calls interface user space with kernel and then there is five main subsystems. These are process scheduler that controls access to the processor, Memory management that permits multiple processes to share memory and uses virtual memory to run portions of processes, Virtual file system that presents common interface to all devices, network interface and finally Interprocess communication.