Advantages and Disadvantages
Advantages :
- Allocating memory is easy and cheap
- Any free page is ok, OS can take first one out of list it keeps
- Eliminates external fragmentation
- Data (page frames) can be scattered all over PM
- Pages are mapped appropriately anyway
- Allows demand paging and prepaging
- More efficient swapping
- No need for considerations about fragmentation
- Just swap out page least likely to be used
Disadvantages :
- Longer memory access times (page table lookup)
- Can be improved using TLB
- Guarded page tables
- Inverted page tables
- Memory requirements (one entry per VM page)
- Improve using Multilevel page tables and variable page sizes (super-pages)
- Guarded page tables
- Page Table Length Register (PTLR) to limit virtual memory size
- Internal fragmentation