Page free space page in sql server

SQL Server uses PFS pages to track the amount of space still available on each page. Page free space (PFS) contains a byte-map. Each page in a database file is associated with a single byte in one of the PFS pages. The byte contains information about how much space is still available on the page as well as a few status bits:

Ø  bits 0-2: how much free space is on the page

·         0x00 is empty

·         0x01 is 1 to 50% full

·         0x02 is 51 to 80% full

·         0x03 is 81 to 95% full

·         0x04 is 96 to 100% full

Ø  bit 3 (0x08): is there one or more ghost records on the page?

Ø  bit 4 (0x10): is the page an IAM page?

Ø  bit 5 (0x20): is the page a mixed-page?

Ø  bit 6 (0x40): is the page allocated?

Ø  bit 7 is unused

A PFS interval is 8088 pages, or about 64MB. A PFS page doesn't have a bitmap – it has a byte-map, with one byte for each page in the PFS interval.

  

PFS(1:1)= 0X44 ALLOCATED 100_PCT_FULL

Means 0x04 is 96 to 100% full (page is full 90-100%)