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What is Web Application , Application Pool and Site Collection in SharePoint.

November 30, 2014

In this article I try to explain difference between web application, application pool & site collections etc. Pretty basic topic but might help someone out there to understand the difference and how each object connects with other and what it does in term of functionality and connections with each other.

I will use an example and your opinion can be lot different than this, if so, please feel free to leave a comment and I will update this accordingly to make concept easier to understand.

Let’s do some definitions first: I know we don’t like definitions but there are easy ones.

Application Pool:

An application Pool is IIS object that contains either one or multiple web applications in it. On a high level application pool reserves or releases memory for web applications (and every thin in that web application) to use and take it back when not in use. It does lot more than this like security & web app isolation but we will discuss about this some other time.

Web Application:

Web application is nothing but just an IIS site. Which, in SharePoint comes with on data base attach to it by default (you can have more than one data bases but for simplicity we will discuss this some other time). Think of web application as an empty container that has nothing inside i.e. No contents.

Site Collection:

From the name it seems like a collection of sites but it’s an object with in the web application. As mentioned earlier the web application is an IIS Site, but site collection is a SharePoint object and you will not see this in IIS, it resides in web application. You can have n number of Site collection in a web application. Usually site collections are our team sites, Project sites etc.

Sub site & Lists, libraries

Sub site is a complete “web site “but it lives with in site collection (and that’s why it is called site collection). There can be n number of sites with in a Site Collection and each site can have a multiple lists and libraries where we store contents


Let’s take an example of an under construction house. All we have is boundary of the house and full basement, so if you go in to house it’s empty, nothing in there and basement is there. This is a web application that has one data base ( basement ) and its empty, address of this house is http://SPHouse and you can see this address in IIS as well.

Let’s build one room in this empty house and few closets and drawers with in this room. This room is our site collection and closets and drawers will be lists and libraries. You can have several rooms in this empty house and this way you will end up many site collections.

In each room you can have several small rooms let’s call them sub sites, these sub sites will always be in that site collection.

Now in technical terms you have one web application that deals with authentication and IIS routing, NLB and much more and within that one web application you can have N number of site collections (rooms), By default each site collection use the same Database that comes with the web application ( our basement) to store all the contents but we use list an libraries with in those site collections to store and manage contents in that data base( let’s say we forgot to build stairs to go in to basement)

Some URL examples (addresses)

This is a very basic overview of each object. But with the new version of SharePoint ( 2013 ) there are several options for HNSC and managed path that allow to configure URLs of end user choice like vanity URLs or dedicated url for each site collections i.e. not dependent on web app url and much more . But I will cover this at some other time as I want to keep it basic for now.

I will try to add some diagram too to help support the architecture of this house, if I find one. Feel free to leave a comment to make it more easier to understand for some folks out there.

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