Whenever possible, it is always recommended to utilize a 64-bit operating system for the database server. When purchasing a new version of SQL Server or Oracle, or when upgrading an existing solution, it is also recommended to utilize the 64-bit edition of the RDBMS. This is because, in a 32-bit environment, the operating system is not able to directly address memory above 4 GB. In a 64-bit environment, the operating system is able to address memory beyond 4GB.
For SQL Server on a 32-bit OS, the maximum amount of directly addressable memory is limited to 2 GB. Additional memory can be addressed using switches, but this adds overhead as the operating system has to manage access to that memory.