Data rows start immediately after the header.

A row offset table starts at the end of the page. The row offset table contains one entry for each row on the page. Each entry records how far the first byte of the row is from the start of the page. The entries in the row offset table are in reverse sequence from the sequence of the rows on the page.

So far we discussed about pages on the disk. A buffer is an 8-KB page in memory. It is the same size as a data or index page. The main memory component in SQL Server is the buffer cache, which is also called as the buffer pool. The buffer cache is divided into 8-KB buffer pages. The database engine requests one or more pages from the data cache when you execute a query to read data from the database. There are two possibilities:

You can see that every database has a name and an ID, and so does each file. Plus, you can see all relevant details in an organized manner.

1. The corresponding page is not available in the buffer cache. A physical read copies the page from disk into the cache.
2. The corresponding page is already available in the buffer cache because of a previous physical read. In this case the current read is only a logical read.
   The space on the disk is managed in units called extents. An extent is made up of eight logically contiguous pages, which is 64 KB of space. To make its space allocation efficient, SQL Server does not allocate whole extents to tables with small amounts of data.

SQL Server has two types of extents:

1. Uniform extents are owned by a single object. All eight pages in the extent can only be used by the owning object.
2. Mixed extents are shared by up to eight objects. Each of the eight pages in the extent can be owned by a different object.

Amaresh Patnaik