Windows XP Operating System - Essay Example

1. Introduction Windows has evolved from a program consisting of 4000 line of s of an assembly language that ran in 8 Kbytes of memory using then Intel 8086 microprocessor to a more complex and robust type of a computer system which runs most of today's computers. In 2000, Microsoft released its new version of the windows called Windows 2000, which are offered to both home PC and professional workstation versions. Its operating system architecture is a hybrid architecture which composed of client/server, layered, object-oriented, and symmetric multiprocessing architecture principles. Windows 2000 borrows from the features of object-oriented languages. An object oriented language is a type of programming paradigm that composed of objects and classes that interact with one another. It has 3 main features such as polymorphism, encapsulation, and abstraction. Windows 2000 features include 32-bit addressing, virtual memory support, system security and enhanced system integrity, platform independence, and built-in modular networking. The Windows 2000 underlying design principles has the essential structure as with later Windows releases (Windows XP Professional/Home/64 bit), Windows 2003 Server). 2. Organizational Architecture The operating system is built upon a layered approach, similar to the UNIX operating system. One advantage of the layered operating structure is that each layer of code is given access only to the layer below it (interfaces and data structures). This structure also allows the operating system to be debugged, starting at the lowest layer and adding one layer at a time until the whole system works correctly. Layering also makes it easier to enhance the operating system; one entire layer can be replaced without affecting other parts of the operating system. Figure 1 illustrates the overall structure of Windows 2000. Figure 1 Windows 2000 Organizational Structure From figure 1, we can see that the Windows 200 (and up) architecture compose of 2 different layers. These are the User mode and the Kernel Mode. The user mode is a layer in which user programs are run. Software in the user mode cannot access hardware directly. From Figure 1, the user mode consists of four sections namely, System Support Process, such as the logon process and the session manager; Service Process, such as event log and scheduled services; Environment Subsystems, which provides an operating system environment by exposing the native operating system services to user applications; and User Applications, such as Task Manager, Windows Explorer, User Applications. The User Applications, do not call the native Windows 2000 OS services directly. They go through a subsystem dynamic link libraries, which translate documented function into the appropriate undocumented Windows 2000 system service calls. The kernel mode has unrestricted access to the system memory and external devices. In this mode, software can access the hardware and system data as well as system resources directly. The kernel mode composed of the following components: Executive, which contains components that implement memory, process, and thread management. It also contains base operating system services such as security, I/O, and internal process communication, which interacts with one another in a modular approach.; Microkernel, which provides multiprocessor synchronization, thread and interrupt scheduling, and exception handling. At system startup, this component reads the information from the system Registry to know which device drivers will be loaded; Hardware Abstraction Layer (HAL), that manipulates the hardware directly by mapping generic hardware commands and responses unique to a specific platform, thus isolating the OS from platform-specific hardware differences; Device Drivers, which translate user Input/Output (I/O) function calls into specific hardware device I/O requests; and Windows and Graphic System, which implements the windows graphical user interface (GUI). 3. Operating System Elements 3.1 Memory Management Windows 2000 (and up) virtual memory manager controls how memory is allocated and how paging is performed. Windows 2000 memory management use what we call virtual memory to allocate memory. Temporary storage used by a computer to run programs that need more memory than it has. For example, programs could have access to 4 gigabytes of virtual memory on a computer's hard drive, even if the computer has only 32 megabytes of RAM. The program data that does not currently fit in the computer's memory is saved into paging files. Paging files are hidden files on the hard disk that Windows uses to hold parts of programs and data files that do not fit in memory. The paging file and physical memory, or RAM, comprise virtual memory. Windows moves data from the paging file to memory as needed and moves data from memory to the paging file to make room for new. The memory manager is designed to operate over a variety of platforms and use page sizes ranging from 4Kbytes to 64 Kbytes. Intel, PowerPC, and MIPS platforms have 4096 bytes per page and DEC Alpha platforms have 8192 bytes per page. 3.2 Concurrency Mechanisms As part of the object architecture, synchronization among threads have been implemented. The two most important methods of synchronization are synchronization objects and critical section objects. Synchronization objects make use of wait functions. The wait functions allow a thread to block its own execution. The wait functions do not return until the specified criteria have been met. The type of wait function determines the set of criteria used. When a wait function is called, it checks whether the wait criteria have been met. If the criteria have not been met, the calling thread enters the wait state. It uses no processor time while waiting for the criteria to be met. The most straightforward type of wait function is one that waits on a single object. The WaitForSingleObject function requires a handle to one synchronization object. The function returns when one of the following occurs: - The specified object is in the signaled state. - The time-out interval elapses. The time-out interval can be set to INFINITE to specify that the wait will not time out. Critical section objects provide a synchronization mechanism similar to that provided by mutex objects, except that critical section objects can be used only by the threads of a single process. Event, mutex, and semaphore objects can also be used in a single-process application, but critical section objects provide a slightly faster, more efficient mechanism for mutual-exclusion synchronization. 3.3 Scheduling Windows 2000 implements a preemptive schduler with a flexible system of priority levels that includes round-robin scheduling within each level and, for some levels, dynamic priority variation on the basis of their current thread activity. Priorities are organized into real time and variable classes. Real time class are threads that requires immediate attention such as communications in real time task. Threads in this class has a fixed priority that never changes. All of the active threads at a given priority level are in a round-robin queue. In the variable priority class, thread's priority changes from an intial assigned value to an up and down changing value over time, thus there is a FIFO (First In First Out) queue at each priority level. Operating system such as windows supports multiprocessor scheduling, a form of scheduling where a computer uses more than one processor. If the operating system is run on a single processor, the highest priority thread is always active and if there is more than one thread that has the highest priority, then the processor is shared, round robin. However, if there are more than one processor, the highest priority threads are always active, running exclusively on the extra processors. The remaining lower priority threads share the single remaining processor. So if there are three processors, the two threads with the highest priority will run on two processors, while the remaining lower priority threads will rub on the remaining processor. 3.4 File System Earlier version of Windows uses a file system called File Allocation System (FAT). This supports Windows 95, MS-DOS, and OS-2. Another version of FAT, the FAT32 was made in Windows 98/SE/ and ME. However, there is a need to meet higher requirements for client/server applications such as database, and file servers, engineering and scientific applications, and network applications for large corporate systems. That is why they developed NTFS (New Technology File System). NTFS is an advanced file system that provides performance, security, reliability, and advanced features that are not found in any version of FAT. For example, NTFS guarantees volume consistency by using standard transaction logging and recovery techniques. If a system fails, NTFS uses its log file and checkpoint information to restore the consistency of the file system. In Windows2000 and WindowsXP, NTFS also provides advanced features such as file and folder permissions, encryption, disk quotas, recoverability, supports for large disk and files , and compression 3.5 Input/Output (I/O) Windows 2000 uses I/O manger which is responsible for all I/O functions and provides a consistent interface among drivers. The I/O manager consists of four modules namely, Cache Manager, File System Drivers, Network Drivers, and Hardware Device Drivers. Cache manager handles caching for the entire I/O subsystem. Caching is the process of temporarily storing recently used data values in a special pool in memory for quicker subsequent access. The cache manager dynamically increasing and decreasing the size of the cache devoted to a particular activity as the amount of available physical memory varies. File system drivers, can be treated as another device driver that routes messages for certain volumes to the appropriate software driver for that device. Network drivers are drivers used to access the networking capabilities of the OS such as local area networking. Hardware device drivers access the hardware registers for a particular hardware peripheral. Windows 2000 consists of two modes of operation: asynchronous and synchronous. In asynchronous I/O , information is sent and received at irregular intervals, at a time. An application instigate an I/O operation and then continue processing while the I/O request is being made, thus optimizes application performance. Synchronous I/O on the other hand, an I/O request is blocked until a previously called I/O is completed. 3.6 Programming Interface Wndows 2000 is a portable operating system in terms of programming interface because of two design decisions. First, the operating system was written in ANSI C, a language that enables programs to be ported easily to other hardware architectures. Second, all parts of Windows 2000 that must be written for a specific hardware are isolated in an area called the Hardware Abstraction Layer (HAL). To move Windows 2000 to a new hardware platform, developers need to do little more than recompile the C code for the new hardware and create a new HAL. Designing an OS around a HAL means that a large portion of the code is exactly the same between hardware platforms. This also means that only the small slice of code that interfaces with the computer's hardware needs to be rewritten as Windows 2000 is ported between different processor architectures. Thus, it provides a high level of portability. 4. Advantages and Disadvantages Windows 2000 and other Windows based operating systems share both advantages and disadvantages. There are many advantages and disadvantages of the Windows Operating System. Some of these are summarized in this section. Windows is a multitasking operating system, unlike its native predecessor from Microsoft, MS-DOS, which can run programs only one at a time, Windows can have different task running. The speed of processing and allocation depends on the computer's physical memory. Another advantages of Windows over almost all OS are the hardware compatibility and device driver's availability. Every windows releases and patches has its own bundle of drivers. Unlike OS such as Linux, it is very hard to get device drivers mainly because hardware manufacturers treat Windows as the world's most used operating system than any other operating systems. Another great advantage of Windows OS is its support to the latest trends in technologies. Microsoft has done an venerable job of supporting new technologies over the years. For example, WinXP supports USB (Universal Serial Bus) 1.x, USB 2.0, FireWire, CD-RW, and a long list of others. Other OS such as the Linux has not kept its pace with these current technologies. Because windows provides a higher level of portability like the Windows 2000, Microsoft has made it easy to install security patches and other reported bugs. However, unlike UNIX and Linux operating systems, windows OS like Windows 2000 and up is said to be single user system, that is designed to be used by one person at a time. Unix and its variants are designed to handle multiple concurrent users. Databases running under Windows allow concurrent access by multiple users, but the operating system itself is designed to deal with a single person at a time. Another disadvantage of Windows is its know vulnerability. Windows has been the target of viruses, worms, Trojans, and other malicious programs for over the years. Also, Windows allows programs to store user information (files and settings) anywhere. This makes it impossibly hard to backup user data files and settings and to switch to a new computer. On the other hand, in other OS like UNIX and its variants, all user data is in the home directory making it much easier to migrate from an old computer to a new one. If home directories are segregated in their own partition, you can even upgrade from one version to another without having to migrate user data and settings. References: Ammann, Paul. Windows 2000 Architecture Prentice Hall PTR. Apr 13, 2001 Stallings, Williams. Operating Systems: Internals and Design Principles, 5th Ed Prentice Hall. 2005 Wikipedia.com "Windows 2000" Horowitz. Michael. "Linux vs Windows: A comparison of Linux and Windows" http://www.michaelhorowitz.com/index.htm Finnie, Scot ."Why Windows Beats Linux". PC Today. May 2004 Read More