Portfolio's folios, each a collection of function calls dealing with a different aspect of 3DO operation, come in two types:

• Permanent, where the folio is constantly in RAM and ready to handle function calls.
• Demand-loaded, where the folio is stored on disk and must be loaded first before tasks can make function calls to the folio.

The Kernel folio is a permanent folio by necessity; it includes the function calls that open other folios. Other permanent folios are the Graphics, Audio, Math, and File folios. Examples of demand-loaded folios include the International and Compression folios.

Demand-loaded folios are automatically fetched from disk when they are needed by a task. When a task tries to open the folio, the kernel first looks in memory for the folio. If the folio isn't found in memory, the kernel then tries to load it from disk. Once the folio has been loaded from disk, it can be used by other tasks in the system without having to reload it.

When demand-loaded folios are no longer in use by any task, the kernel can remove them from memory to make the memory available to other uses in the system.