Some Key Enhancements in 2.5 kernels

2.5 Was first kernel where "Enterprise" functionality became a key focus

Scalability
8 to 16 to 32 way SMP depending on hardware platform
Scheduler improvements
Per-CPU timers, counters, statistics

VMM Enhancements
Support for 32 GB of memory on IA32
Large page (2/4 MB) VM support
Large page in-memory filesystem support

Improved threading model
Particularly beneficial for large numbers of threads/processes