The buffer management component consists of two mechanisms: the buffer manager to access and update database pages, and the buffer cache (also called the buffer pool), to reduce database file I/O.

The Buffer Manager, as its name suggests, manages the buffer pool, which represents the majority of SQL Server’s memory usage. If you need to read some rows from a page, the Buffer Manager checks the data cache in the buffer pool to see if it already has the page cached in memory. If the page is already cached, then the results are passed back to the Access Methods.

If the page isn’t already in cache, then the Buffer Manager gets the page from the database on disk, puts it in the data cache, and passes the results to the Access Methods.