Git Book - The Git Object Model

The SHA All the information needed to represent the history of a project is stored in files referenced by a 40-digit "object name" that looks something like this: 6ff87c4664981e4397625791c8ea3bbb5f2279a3 You will see these 40-character strings all over the place in Git. In each case the name is calculated by taking the SHA1 hash of the contents of the object. The SHA1 hash is a cryptographic hash