Microsoft does not offer a free, legal public download for SQL Server 2008 R2 Standard Edition. The free version is Express Edition (which has a separate ISO). Be wary of sites offering "free full version" – they are scams.
The 64-bit ISO requires a 64-bit OS:
By the late 2000s, the transition from 32-bit to 64-bit computing was no longer optional. SQL Server 2008 R2 Standard Edition capitalized on the x64 architecture to break the fundamental 4GB memory barrier that plagued its 32-bit predecessor. On a 64-bit system, the Standard Edition could address up to 64GB of RAM (a substantial increase from 32-bit’s 4GB limit, with only 2GB usable by default without AWE). sql server 2008 r2 standard edition 64 bit iso
This memory headroom transformed database performance. Entire datasets could reside in memory, drastically reducing physical I/O bottlenecks. For the Standard Edition—often deployed on dual-socket servers in SMB environments—this meant running OLTP workloads and large reporting instances without requiring the exorbitant licensing of the Enterprise Edition. Microsoft does not offer a free, legal public
Today, the 64-bit ISO image of SQL Server 2008 R2 Standard Edition serves three niche purposes: The 64-bit ISO requires a 64-bit OS: By