Windows XP is the latest and most robust of the family of all windows operating systems that are popular with PC users worldwide. Windows XP comes in two editions namely the home edition and the professional edition to cater to the varying needs of the respective class of users. One of the main problems with the previous versions (9x) of windows operating systems was that they were prone to frequent system crashes. Microsoft, the developer and marketer of the Windows operating systems, addressed this problem by designing Windows NT based on a new technology that increased the stability and minimized system breakdown. However, this stability was compromised by the lack of compatibility, as NT was selective about the hardware. Microsoft later developed and released windows XP as an operating system for both the desktop as well as the server systems. XP has the compatibility of the earlier Windows 9X versions and at the same time is highly stable and resistant to crashes. Let us study the architecture of Windows XP, and in the process understand, the memory management, process management, device management, file handling functions and other aspects of the operating system. Memory Management

Memory management is one of the important functions of an operating system. Allocation of memory to applications is a complex task and the frequent problem is that of applications trying access memory regions, which are beyond their preset limits resulting in overwriting memory regions allocated for other applications. This problem, known commonly as clobbering, leads to repeated system crashes. Windows XP, by using a protective memory model, tries to overcome this menace. The maximum amount of addressable memory in any 32-bit operating system is 4,294,967,296 or in other words 4Gb. Though theoretically it is possible to address and operate 4GB of memory space in reality most computers do not have 4GB of memory. However, operating systems make use of the concept of virtual memory to circumvent this limitation. [SYBEX Inc., 638]

Virtual memory refers to the use of hard disk space as part of the memory. Applications are supplied with more memory area than the computer could manage at any given moment of time. The Virtual memory manager jumps into action whenever an application tries to access a page that is currently not available within the physical RAM. The Virtual Memory manager in Windows XP uses the concept of paging to handle this task. Virtual address space is neatly divided into units called pages and the transfers between memory and disk are always carried out in units of a page. Only parts of the program that are currently needed by the application are stored in the RAM and the rest are stored in a page file. A page fault is said to occur when an application tries to access parts of the program, which are currently not in the physical RAM. In a real timesharing situation processes are switched back and forth between main memory and disk and the process is referred to as swapping. [Andrew S. Tanenbaum, 89]

Another novel feature in Windows XP is the memory protection model that it employs. Windows XP recognizes two levels of privilege for any process namely the kernel mode and the user mode privileges. Based on the access privileges Windows XP either allows or disallows any process from reading from or writing to any particular block of memory. Windows XP has many new features such as 'logical prefetcher or the fast boot application launch', 'increased page table entries' and 'reduced paged pool' usage all of which contribute directly to improved memory management. Once Windows XP is booted it automatically saves data about all disk read operations. The 'logical prefetcher' is designed to minimize the number of disk seeks by prefetching data which are frequently accessed by the application. Dynamic paged pool is another new feature, which facilitates quicker response time for applications. Windows XP also dramatically improves the server response time because it makes use of 'individual page charging' scheme whereby a server can understand multiple requests for the same page and hence minimize storage requirements. [Microsoft Corporation]

Process Manager

Windows XP follows the process model for execution of programs. One of the key points is that XP is designed on the 'Client Server model' or what is called as the micro kernel model. The essential idea behind the client server model is that parts of the operating systems consider themselves as clients or servers. As always, the kernel is considered the core of the operating system and keeps track...

However, as against most of the modern operating systems, Windows XP does not put everything other than the applications in the kernel mode. Instead it puts only a minimum part of the operating system in the kernel mode and leaves the rest of the operating system in the user mode. Kernel mode programs are a cause for concern because they have access to system memory areas. Since in the client server architecture only the bare minimum portion of the operating system is kept in the kernel mode the chances of a system breakdown due to overwriting of system memory area is greatly reduced. It is this factor, which accounts for the high stability of Windows XP compared to the previous versions. [SYBEX, 619]
Device manager

The device manager feature built within the operating system makes the task of managing the various devices a lot simpler. Windows considers each device as a file and each device attached to the system has its own device driver. The device drivers are responsible for accepting and executing the requests from device independent software. For using a device, a suitable device driver is a prerequisite. In other words device driver is the software, which has information about a device and how to communicate with that device. Windows XP comes with a large number of device drivers that are supplied by the respective vendors. These device drivers are installed on the computer when the operating system is installed for the first time. The '%systemroot%Driver Cache i386' folder has all the drivers for the devices that are attached to the system. Windows XP has a driver update feature, which updates the latest drivers for devices. [Guy Hart - Davis, 182]

Since device drivers are essential for the communication between the operating system and the devices the operating system runs the drivers in the kernel mode. This however implies that a badly written driver could potentially crash a system. The problem is further complicated by the fact that drivers are written by different device vendors. One special feature in Windows XP is the implementation of a quality control check for device drivers. Windows XP includes a routine check for a digital signature, which ensures that the particular driver is compatible and is not tampered with. Every time Windows XP comes across a driver that does not carry a digital signature for its quality it flashes a warning message to the user. Windows XP professional automatically allocates the system resources to the hardware devices. Requirements such as interrupt requests, input/output base addresses, memory address and direct memory access channels, are automatically handled by the operating system. The windows 'Device Manager' offers the easiest way to handle the devices. [Guy Hart - Davis, 183]

File Manager

Files are indispensable when we work with computers and they offer permanent storage for our data. Windows XP supports three main types of file systems namely FAT16, FAT32 and NTFS. The NTFS system is by far the most preferred method of file storage as it has may advantages over the FAT 32 format. The transaction logging feature and checkpoint information allow for data consistency even in the case of a system failure. In the NTFS format even very large files (sparse files) can be created requiring only a little disk space. However the negative side of NTFS format being that it requires more maintenance and hence incurs a compromise on performance compared to FAT systems. Further, NTFS is not downward compatible with win 98, MS DOS, WIN ME etc. [Jason Zandri]

Files are organized under folders, which may further contain child folders. Windows XP stores files as clusters in any format that is suitable for the particular media in which the data is stored. Typically for a floppy drive FAT12 is used and for the hard disk the NTFS format is common. XP allows filenames to be as long as 260 characters, which also includes the path to the file. Explicit file and folder level permission restrict access to vital data to individual or group users. Read, write and execute permissions for files and folders further improve the control over information sharing. Unlike Unix or Linux, Windows XP is not case sensitive. Windows XP stores filenames in their long format however it also maintains shorter 8.3 format so that 16 bit applications can access them without any problem. The windows explorer provides an easy way to navigate between folders and files. The back up utility provides for recovering data in…