Hi,

I did not find my custom assembly neither in bin folder nor in GAC, but I have found it in Solution Gallery of site collection.

So, is the Solution Gallery equivalent to both bin and GAC?  

I think all solution that are in Solution Gallery have been stored inside the Database, is that right??

Thanks

The solution gallery is stored in the database and serves a special purpose.  custom assemblies that are stored in the solution gallery are Sand box solutions and they have specific limitations. You can read more about htem here:

https://msdn.microsoft.com/en-us/library/office/ee539083(v=office.14).aspx 

But custom code in sand box solutions has been deprecated and will be going away in a future version.

Hi,

As Paul suggested the sandbox solution will goes away in future version and in deprecated in the SharePoint 2013,works in backward compatibility mode. 

Any how the WSP you found in the Solution Gallery will have the assembly and its references will be stored in the content database of the site collection.

When the request has been initiated to run the sandbox solution, all assemblies will be extracted to the below location of the SharePoint Server and SPUCWorkerProcess.exe will use this location to run.

C:\ProgramData\Microsoft\SharePoint\UCCache

Its just for information purpose not to do anything with that loc