Git's internal data structure is a tree of data objects, wherein each objects only points to its predecessor. Each data block is hashed. Modifying (bit error or attack) an intermediate block will be noticed when the saved hash und the actual hash deviate.
How is this concept different from block chain?
Git is not listed as an example of block chains, but at least in summaries, both data structure descriptions look alike: data block, single direction reverse linking, hashes, ...).
So where is the difference, that Git isn't called a block chain?
git is not an example of blockchain technology for several reasons (these were the first that came to mind):
In a blockchain implementation, every block is verified independently multiple times before it is added to the blockchain. This is indeed one of the most important things about blockchain technology and is what ensures its "unhackability." On the other hand, many
git projects do not require independent verification and, when they do, they only require one person to sign off on a change before it is committed to the repository. Hence, with at most one point of validation that you must trust,
git breaks one of the core tenets of blockchain technology.
git repository is not necessarily duplicated on many servers. You can work from a
git repository locally and if your local disk were corrupted, you would lose everything. Blockchain technology implies the reproduction of the ledger across servers.
You can rewrite
git history. A
git push <remote> <branch> --force where
<branch> is set to a previous state than that at
<remote> would rewrite the history. In blockchains, the ledger is an immutable history.