Any part of the main memory that is available for I/O operations is managed in the I/O buffer cache. When the database instance is started, the I/O buffer cache is created in the main memory in accordance with the size entered in the general database parameter CACHE_SIZE.The size of the main memory is given in pages.
The primary consumers of the main memory managed in the I/O cache are the converter and the data cache. If the converter grows while the database is running, and requires more pages, it is given pages from the I/O buffer cache. If the pages run out here, data is displaced from the data cache and given to the converter.