OS/2 allocates and commits memory objects in pages. A memory page is a 4KB (4096 bytes) piece of memory. Memory access protection is also done on a page-basis, rather than the segment-based protection used in previous versions of OS/2.
A page range is a linearly contiguous group of pages within a memory object. A page range can be any of the following:
If an application requests 512 bytes of memory, it will receive a 32-bit pointer to a 4KB page. All 4096 bytes are available to the application, even though the request specified only 512 bytes. If an application requests 62000 bytes, it will receive a pointer to a 65536-byte (64KB, 16-page) object. Again, all 65536 bytes are available for use.
Each page in the virtual address space of the process is either free (unallocated), private (available only to the process that allocated it), or shared (memory that is shared between processes).
Each page within a memory object can be in one of two states, either uncommitted (that is, the linear address range has been reserved, but is not yet backed by physical storage) or committed (physical storage has been allotted for the logical address range).
Access to a committed page is controlled by the page's access protection attribute. These protection attributes are read access, write access, execute access (on the 80386, this is the same as read access), and guard page access.
An uncommitted page is not accessible.