iisreset -- 对象是整个IIS服务器，这个操作会先停止万维网的服务（World Wide Web Publishing Service）然后在重启此服务，因此所有的网站都会先停止服务然后在重新开始服务。
As pointed out, iisreset will stop and start the World Wide Web Publishing Service. This, of course, applies to all of your application pools. I'm sure you noticed a process being created for each application pool. This process will handle requests for all websites associated with it.
Recycling -- 对象是一个应用池（Application Pool）,IIS会在此应用池下面新建立一个进程，并且会暂时保持原有的进程。建立新的进程之后所有新的请求都会转移到新的进程中，然后过一段时间关闭原始的进程。（此处还是有疑惑的，老的请求是会直接转入新的进程，还是继续由原始进程来服务？有待考证）
When you recycle an application pool, IIS will create a new process (keeping the old one) to serve requests. Then it tries to move all requests on the new process. After a timeout the old process will be killed automaticaly. You usualy recycle your application pool to get rid of leaked memory (you might have a problem in your application if this needs to be a regular operation, even though it is recommended to have a scheduled recycle).
Restart -- 对象是一个网页（Website），所有服务仍然会在同一个进程池中保持服务的状态。但是所有的会话（Session）会断开然后重新连接。
As for restarting a website, it just stops and restarts serving requests for that particular website. It will continue to serve other websites on the same app pool with no interruptions.
If you have a session oriented application, all of the above will cause loss of session objects.
Refresh -- 对象是IIS Manager本身，此操作不会影响任何服务，只是会刷新左侧的树状列表。
Refreshing a websites has no effect on the service/process/website and is meerly a UI command to refresh the treeview (maybe you added a directory you don't see in the management console).
Reference：
http://serverfault.com/questions/247425/what-is-the-difference-between-iisreset-recycle-refresh-and-restart
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