Questions about Informix page buffers

Hi, in reading the Informix documentation, it mentions that page buffers are used to cache data from disk. It mentioned that the page size and number of pages are dependent on the database server and O/S. I am unclear on what the dependencies are other than the available memory and the abilities of the server to manage the buffers. What are the ranges for Informix-OnLine 6.0 (assuming unlimited memory available)? Also is there a way to allocate page buffers to a specific database, table, index? I would like to ensure that certain tables and indices remains cached even after a large transaction which could wipe-clean a shared cache. Any info would be appreciated. Thanks John