Memory cont. #

Page tables / addressing cont. #

• the more hierarchy you have, the more memory accesses you need

Hashed page tables #

• we can use either method of resolving collision in the hash table: chaining or linear probing

Inverted page table #

• instead of keep track of logical pages, we keep track of physical pages
• notice that we add a new field to the logical address: pid
• a linear search is involved at worst case, so the page table can be improved by using a hash table

Virtual memory #

Memory for the point of view of the program.

• how can we run a program that will use more memory than totally available?
• we’ll just load what is necessary

When to load a page? #

• pages with the invalid bit do not have a frame number

Page fault #

If there is a reference to a page, but it is not in memory, it causes a page fault.

Demand paging #

• evicted pages go to swap, incase we need to bring it back soon
• swap space can be in memory, or on hard drive

Page replacement algorithms #

• looks at when page was loaded, picks the oldest
• implement with FIFO queue

• theoretically the best, but relies on knowing the future