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Terms in this set (12)

What is a page fault?
When a process accesses a page that is not assigned a frame in the page table (i.e. the pfn field is not valid at all) and needs OS assistance in finding a free page and updating the page table entry
Why is the clocksweep algorithm better than the random algorithm?
We want to minimize the number of times that a frame we are trying to access is not in memory, causing us to go to disk. Recently accessed frames can be predicted to be reassessed again in the future. The clocksweep 'referenced' bit allows us to do this by first trying to find a not-recently-accessed frame that we may evict.
What is the swap in a page table entry used for?
Refers to the corresponding swap entry for the page table entry
What is a dirty (page table entry) bit used for?
Bit to indicate that the page has been written to in memory but not updated in swap
What is a valid (page table entry) bit used for?
Bit to ensure that the page entry is mapped onto a physical frame in memory
What is the frame table?
Maps the frame table entries to their corresponding process and process VPN
you can index into it to get a specific frame table entry using its PFN
What is a frame?
Allocations in physical memory where pages are stored
What is a page table?
- Addressable by the virtual address and maps each page of a process to its corresponding frame in physical memory.
- One page table per process
- Has valid, dirty, pfn, and swap bits/entries in it's struct
What is a page?
A page is a part of a process (i.e. code, stack, heap, data, etc.)
What is the protected bit? (Frame Table Entry)
1 if the frame holds a page table and is immune from eviction, 0 otherwise
What is the Page Table Base Register (PTBR)?
- PTBR tells the paging hardware where to find the currently running process's page table
- Can be set using context_switch function via the process's "saved_ptbr" member
- More specifically, if P1 is the currently running process, and P1 has it's page table stored in frame number 5 of physical memory, then PTBR will store 5.
What is a page size?
The size of every page and every frame. (this fixed size causes internal fragmentation, but removes external fragmentation.)
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