WebPart Deployment

Within a SharePoint site, we can deploy a Web Part assembly in any of the following locations.
bin directory — The bin directory is a folder stored in your Web application root directory. For most installations, this is located in the %SYSTEMDRIVE%\inetpub\wwwroot\wss\VirtualDirectories\\bin directory.
Global Assembly Cache (GAC) — The GAC enables you to share assemblies across numerous applications. Components are typically installed in the %SYSTEMDRIVE%\WINDOWS\Assembly directory.
Note that the recommended practice is to deploy assemblies to the bin directory.
Windows SharePoint Services provides a SafeControls list to prevent users from arbitrarily adding server-side code within ASPX pages. The SafeControls list is a list of approved controls and Web Parts that are specific to the SharePoint site that we have designated as safe for invocation on any ASPX page within our site. This list is contained in the web.config file in your Web application root. The local path contains the physical location of the web.config file.

Web Parts are designed to be distributed over the Internet or an intranet. For security reasons, when we create a custom Web Part, we should give it a strong name to ensure that the Web Part can be trusted by our users.

By default, the trust level for a server will be WSS_Minimal, which does not allow access to the Windows SharePoint Services object model. In order to perform such actions, we must perform one of the following three actions:

Create a custom policy file for your assembly,
Install your assembly in the GAC global assembly cache
Increase the trust level for the entire virtual server. Eg: increase the default trust from WSS_Minimal to WSS_Medium in the web.config file.