What is a load all subfile?

A load all subfile is one in which we generally specify the subfile size as 9999 in the record format itself. However, you may define the subfile size to be less than 9999 in the record format and still load all your subfile at a time. In that situation the records will not be placed at contiguous memory location.

So, conceptually a load all subfile is the one in which all records are loaded at one go before they are displayed. Also, they should occupy contiguous memory locations.

What are single page subfiles?

A single page subfile is a subfile in the number of records loaded at a time is equal to the maximum number of records which can be displayed at a time. In other words in a single page subfile all loaded records are displayed at a time. We delete all previously loaded records from the subfile whenever we need to load the next page of the subfile.