Drawing styles
We will now see the different representations available for the Memory subsystem.
Virtual Memory
Not valid page. Any access will cause a page fault.
Valid page. This page has not been modified since it was loaded into memory or since the last time it was written to swap space. So it could be discarded if needed and it's frame given to another page.
Valid page. This page has been modified since it was loaded into memory or since the last time it was written to swap space. So it we need the memory frame for a different page we would have to write it to swap space before reassigning it.
This page is not valid, but a frame as been assigned to it and will soon be valid.
Physical Memory
This represents physical memory frames which get assigned to process' pages.
This frame is free.
This frame is assigned to process 1 and has been modified since it was loaded, so it will have to be written in swap space before it can be reused for a different page.
This frame is assigned to process 2 and was not modified since it was loaded, so it may be discarded without writing it to swap space if needed.