Encyclopedia of Computer Science and Technology

308 Microsoft WindowsIntroduced in 2007, Microsoft Windows Vista features bettersecurity, a 3D look, new search facilities, and multimediafeatures. (Microsoft Corporation)appears to be a combination of “back to basics” (a responseto the sluggish performance of Vista) and more seamlessuser access to data and media from a variety of sources.User’s PerspectiveFrom the user’s point of view, Windows is a way to controland view what is going on with the computer. The userinterface consists of a standard set of objects (windows,menus, buttons, sliders, and so on) that behave in generallyconsistent ways. This consistency, while not absolute,reduces the learning curve for mastering a new application.Programs can be run by double-clicking on their icon onthe underlying screen (called the desktop), or by means ofa set of menus.Windows users generally manage their files througha component called Windows Explorer or My Computer.Explorer presents a treelike view of folders on the disk.Each folder can contain either files or more folders, whichin turn can contain files, perhaps nested several layers deep.Folders and files can be moved from place to place simplyby clicking on them with the mouse, moving the mousepointer to the destination window or folder, and releasingthe button (this operation is called dragging). Anotheruseful feature is called a context menu. Accessed by clickingwith the right-hand mouse button, the menu bringsup a list of operations that can be done with the currentlyselected object. For example, a file can be renamed, deleted,or sent to a particular destination.Windows includes a number of features designed tomake it easier for users to control their PC. Most settingscan be specified through windows called dialog boxes,which include buttons, check boxes, or other controls. Mostprograms also use Windows’s Help facility to present helppages using a standard format where related topics can beclicked. Most programs are installed or uninstalled usinga standard “wizard” (step-by-step procedure), and wizardsare also used by many programs to help beginners carry outmore complex tasks (see help systems).MultitaskingFrom the programmer’s point of view, Windows is a multitasked,event-driven environment (see multitasking).Programmers must take multitasking into account in recognizingthat certain activities (such as I/O) and resources(such as memory) may vary with the overall load on thesystem. Responsible programs allocate no more memorythan they need, and release memory as soon as it is nolonger needed. If the pool of free memory becomes too low,Windows starts swapping the least recently used segmentsof memory to the hard drive. This scheme, called virtualmemory, allows a PC to run more and larger programs thanwould otherwise be possible, but since accessing the harddrive takes considerably longer than accessing RAM, thesystem as a whole starts slowing down.Windows also has a rather small amount of memoryreserved for its GDI (Graphics Device Interface), a systemused for displaying graphical interface objects such as icons.If this resource pool (which has been made somewhat moreflexible in later versions of Windows) runs out, the systemcan grind to a halt.Programming PerspectiveProgrammers moving to Windows from more traditionalsystems (such as MS-DOS) must also deal with a new paradigmcalled event-driven programming. Most traditionalprograms are driven by an explicit line of execution throughthe code—do this, make this decision, and depending on it,do that—and so on. Windows programs, however, typicallydisplay a variety of menus, buttons, check boxes, and otheruser controls. They then wait for the user to do something.The user thus has considerable freedom to move about inthe program, performing tasks in different orders.A Windows program, therefore, is driven by events. Anevent is generally some form of user interaction such asclicking on a menu or button, moving a slider, or typinginto a text box. The event is conveyed by a message (seemessage passing) that Windows dispatches to the affectedobject. For example, if the user presses down (clicks) the leftmouse button while the mouse pointer is over a window, aWM_BUTTONDOWN message is sent to that window.Each of these interface objects (collectively called controls)has a message-handling procedure that identifiesthe message. The object must then have appropriate programcode that responds to each possible type of event. Forexample, if the user clicks on the File menu and then clickson Open, the code will display a standard dialog box thatallows for selecting the file to be opened.Fortunately for the programmer, Windows providesdevelopers with a large collection of types of windows, dialogboxes, and controls that can be displayed using a functioncall. For example, this code (after some preliminarydeclarations), displays a type of window called a list box:HWND MyWindow;hMyWindow = CreateWindow(“LISTBOX”,“Available Services”,WS_CHILD|WS_VISIBLE,0,0,100,200hwndParent,NULL,hINst,NULL);