Virtual memory: design issues
Design issues for VM are related to HUGE cost of a miss (page fault)
Accessing disk may take MILLIONS of clock cycles
  - Pages should be large enough to cover the cost of page fault
4KB to 16KB common
  - Reducing page fault rate has high priority
fully-associative page placement
  - Page faults can be handled in software
overhead is small compared to cost of disk access
use clever algorithms to minimize page faults
  - Write-through is too expensive
use write-back to store data