When a program is selected for execution, the system brings it into virtual storage, divides it into pages of 4 kilobytes (4K), and transfers the pages into real storage for execution. To the programmer, the entire program appears to occupy contiguous space in storage at all times. Actually, not all pages of a program are necessarily in real storage, and the pages that are in real storage do not necessarily occupy contiguous space.
The pieces of a program executing in virtual storage must be moved between real and auxiliary storage. To allow this, z/OS manages storage in units, or blocks, of 4 kilobytes.
The following blocks are defined:
– A block of real storage is a frame.
– A block of virtual storage is a page.
– A block of auxiliary storage is a slot.
A page, a frame, and a slot are all the same size: 4096 bytes (4 kilobytes). An active virtual storage page resides in a real storage frame. A virtual storage page that becomes inactive resides in an auxiliary storage slot (in a paging data set).