Microsoft's announcement that Windows Server 2008 R2 would ship exclusively as a 64-bit platform was a watershed moment. For the first time, a major server OS dropped 32-bit support entirely.
Why it mattered: 64-bit addressing removed the ~3.5 GB RAM ceiling that had plagued 32-bit systems. Servers could finally leverage 8, 16, or even 128+ GB of memory — a requirement for the virtualization and database workloads that were rapidly becoming standard.
This decision also pushed hardware vendors and driver authors to commit fully to x64. Within a few years, 32-bit server deployments became rare outside of legacy environments.
The security angle: 64-bit platforms enabled hardware DEP (Data Execution Prevention) and kernel patch protection (PatchGuard), making entire classes of exploits significantly harder. It was a net win for both performance and security posture.
Looking back, this was one of those strategic decisions that aged exceptionally well.