[TheDong]

If you don't have mining, or a similar way to decide between various possible forks, what you have is a cryptographically secured append-only ledger (such as what the git data-format resembles).

That's not a blockchain and that idea has existed for decades already.

I think that idea is now being called a "blockchain" since in reality the trustless/proof-of-work nature of a true blockchain is largely wasted for specific companies.

[tscs37]

It's a blockchain if you have a directed linked list of blocks. Even git is to some extent blockchain.

[TheDong]

That's a redefinition of what a blockchain is IMO.

That's definitely the definition some companies are operating under.. but really?

WALs and journals have existed for ages and both fit the definition of a directed list of blocks.

Hell, ext2 and FAT fit that definition (inodes forming a directed list of block-references).

I guess we all store our data on something that's technically a blockchain by your definition.

[tscs37]

It's not a redefinition, it's a definition that has been around since the 1990's [0], the only requirement for a blockchain is A) directed linked list (block points to previous block) and B) cryptographic security (use hashes as block index)

Bitcoin is merely the first application to use Blockchain in a decentralized proof-of-work manner.

[jacquesm]

A git repository is a Merkle tree.

http://en.wikipedia.org/wiki/Merkle_tree

A bitcoin blockchain is also a Merlke tree.

But a git repository is not a blockchain.

[tscs37]

It is a blockchain is you don't merge since you have a commit pointing at a previous commit, (block points to block), merges point to two parents but Ethereum has that almost with uncle blocks.

The commit log of a repo is almost certainly a blockchain, which is why I mentioned "to some extend"

[jacquesm]

You are simply wrong.

Think of a blockchain as only one strand (say, the leftmost strand, from a leaf all the way to the root) of a Merkle tree. Think of a git repository as the whole tree. So no, they are not equivalent.

If they were there would never be a way to have more than one branch depend on a previous one.

[TheDong]

You didn't include the reference link. The term "blockchain", as used these days, refers to the distributed system underlying cryptocurrencies.

That's not a thing that has existed since the 90s nor is it a thing with so few requirements.

[tscs37]

The first paper on blockchains was published in January 1991 (revised/received in 1990) [0]

>The term "blockchain", as used these days, refers to the distributed system underlying cryptocurrencies.

That's how you prefer to use it but it doesn'T change how it's defined [1]

[0]: https://link.springer.com/article/10.1007/BF00196791

[1]: https://en.wikipedia.org/wiki/Blockchain

[sirclueless]

The common consensus for the term "blockchain" is not based on the 1991 paper, but on Bitcoin's use of similar technology to make a distributed ledger. The term itself is relatively recent, and was not used until well after Satoshi's paper. For example, Harvard Business Review describes it this way:

"At its most basic, blockchain is a vast, global distributed ledger or database running on millions of devices and open to anyone" [1]

That incorporates at least two concepts that are typically associated with the term "blockchain" that go beyond the basic cryptographic data structure: they are distributed, and they are open. Lots of technologies use a similar data structure; git uses a similar data structure. But when a silicon valley startup comes to you and pitches you on their "hot new blockchain tech" they probably don't mean git.

[1]: https://hbr.org/2016/05/the-impact-of-the-blockchain-goes-be...