Chapter 3. z/VSE overview 83
All page frames assigned to virtual pages are queued in the page selection
queue (PSQ). New pages are queued at the end. The position in the queue
indicates how long relatively it has been since a program referenced the page.
When a page frame is needed from this queue, the system scans the PSQ from
the beginning and checks the reference bit of a certain number of page frames. If
the reference bit is on, it is reset and the page frame is requeued at the end of
the PSQ.
The first page frame found with change bit and reference bit off is the one used
for replacement. It is the
oldest inactive page frame, because it has moved from
the end of the PSQ to the bottom without having been referenced.
3.4.6 What is storage ...