Paging

Performance Critical
Applications always want more memory than available
Disk is thousands of time slower than memory
Smart decisions yield dramatic results

Monolithic Kernel
All mechanism and policy is centralized in the kernel
VMM has global knowledge
Intimate with caches, file systems, etc.
Resource limits

Multiserver OS
External paging
File systems et al in user space
Servers provide services on behalf of clients
Servers do not trust each other