Server Environment Factors that Affect Performance

Server environment includes Processor Cores, RAM and Storage type (affecting processing ability), Operating System, Database Server and transfer bandwidth suitable to meet required work load.

Server Computing Resources

Server’s hardware resources like Processors/Cores, RAM, the free space on the server storage media that in-turn affects the size of cache files and paging files that can be created on the drive, and the efficiency of the storage media, all have a major impact on the server performance in serving the tests to a group of candidates.
If there are more processes running on the server, it is always suggested to keep surplus resources to make available minimal resources for test process at any point of time.

Operating System

The other major factor that is considered a component of the server resources is the version of OS installed. There are maximum RAM usage limitations for Operating Systems. So even if you have multiple Processor Cores and high RAM on your system and higher version of SQL, still if the OS has a limitation, it will form a bottleneck.

Operating System

Version	Limit on X86	Limit on X64
Windows Server 2008 Standard	4 GB	32 GB
Windows Web Server	4 GB	32 GB
Windows Server 2008 R2 Standard	-	32 GB
Windows Web Server R2	-	32 GB
Windows Server 2008 Enterprise	-	2 TB
Windows Server 2012 Standard	-	4 TB

Database Server:

Similarly, various versions of SQL have their respective limitations on the maximum amount of memory that they can use. So even if you have deployed a server with 64 GB RAM, but it is installed with SQL Express edition, the SQL shall not be using memory more than 4GB, and this would form the bottle neck in serving more than 10-20 users. So it is suggested to install SQL standard or Web edition with minimum 32 GBs to meet a workload of upto 50 concurrent users.

To know more about SQL server variants, refer the following link:
https://msdn.microsoft.com/sv-se/library/cc645993(v=sql.110).aspx