Adaptive Server tries to keep the page allocations close together for objects. In most cases:
If there is an unallocated page in the current extent, that page is assigned to the object.
If there is no free page in the current extent, but there is an unallocated page on another of the object’s extents, that extent is used.
If all the object’s extents are full, but there are free extents on the allocation unit, the new extent is allocated in a unit already used by the object.