In SharePoint, all pages have two different states called "Ghostable" and "Unghostable". [Note - it is state not type]. By definition, Ghostable pages are the ones that are present in file system [i.e. which is present in SP server - mainly the WFE] and UnGhostable pages are the ones present in content DB. [stored in SQL Server].
All application pages [ex. settings.aspx page of any site ] getting loaded from "/_layouts/15/ " folder are ghostable pages because they are built dynamically when requested.
Normally, when a page is requested, it goes and hits the contentDB. There is a flag for ghosted/unghosted, if any pages are customized, the flag is set to true and page is parsed and taken directly [binding of page template and customized component. It happens in runtime itself.
This process is executed by VPP [Virtual Path Provider]
VPP does both jobs (Ghosted and Unghosted) for single request of page. First, it reads template page (ghosting), second it reads instance of page (unghosting), and then combines both parties and renders the page.
VPP is part of IIS [Internet Informatiom services]. The main functionality of IIS is to handle requests & provide responses. There are many functionatilities handled by IIS but the main functionalities are listed below.
- Authenitication
Deciding which authentication protocol to use. For example, the Default Web Site might be intended as a public-facing Web site for Internet users. As such, it might be configured to allow anonymous access and to support Basic Authentication. A secondary IIS Web site intended exclusively for employee use within the corporate LAN might be configured to disallow anonymous access and to support Integrated Windows Authentication
- Configuration Settings
Creation and configuration of virtual directories. A virtual directory is an entity that defines a child URL space nested within the URL space of its parent IIS Web site. Like an IIS Web site, a virtual directory is configured with a root directory on the file system of the hosting Web server.it is used to inspect, create, and configure IIS Web sites and virtual directories on the current machine/host server [WFE- Web front End]
Navigation -> run-->cmd-->inetmgr
[or]
Start-->Control Panel -->Administrative Tools-->IIS
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Note
That is the main reason we attach w3wp.exe while creating farm solution to debug. Also, use different application pool for different web applications created in SharePoint server, for managing the Server resources effectivitely and for security reasons [during the configuration of service application, like UPA, BDC, MMS etc.]
This article, in short, explains how this web application is created in IIS using Windows SharePoint services, what are ghosted/unghosted files and things related to Application pool. It is a small overview of SharePoint architecture.