[kang]

> a ledger is just an indelible, append-only log of transactions that take place between various parties.

Readers should decide either the above statement is true and ethereum is not a blockchain by that definition[0] or blockchain is just an abstract buzzword. Technology wise, git is as powerful as a blockchain at being an append-only log without the most important ingredient - proof-of work.

2. There is a whole section on private blockchains

Can you write one program using a private blockchain(for eg use ibm's hyperledger) that can't be written using git? Private blockchains, premined coins, colored tokens, assets etc all of them.

3. Regarding smart contracts, can you show me one use of turing completeness in a blockchain? If yes, ethereum is not turing complete practically cause gas.

4. How does one determine the gas price of an opcode in a network? How does ethereum do it? (i think only people understanding need of proof-of-work will understand this)

5. W.r.t the layers of OSI model, the need for smart contract is trivial. Show me one smart contract you can do 'in' a blockchain and I will tell you how to do it 'on' bitcoin.

[0]https://ethereum.stackexchange.com/questions/9535/how-does-a...

[yarrel]

From [0] - "The transactions were not rolled back. The ETH amounts were just transferred automatically at 1,920,000 ."

So a transaction did take place "between various parties", nothing previous to block 1920000 was changed, and the transfer is there for all to see.

[mannykannot]

No amount of wordplay and denial will alter the fact that the DAO fork was a de-facto rollback.

[DennisP]

There's a fundamental difference: a rollback reverses everybody's transactions, the DAO fork left unrelated transactions alone.

Bitcoin had an actual five-hour rollback in its early days, when someone figured out an exploit and awarded themselves over a billion coins.

[codehalo]

That’s incorrect. There was never a rollback in Bitcoin. You may be referring to the leveldb bug that caused a fork, or Gavin and Satoshi’s discovery of the billion coins bug, which was fixed by a software update, but none of these involved a rollback.

[DennisP]

I was thinking of the billion coins bug. I did some searching and it appears you're mostly correct; the errant transaction was removed, along with subsequent transactions that descended from it, but unrelated transactions were left in place.

https://bitcointalk.org/index.php?topic=823.msg9557

[mannykannot]

A rollback followed by a replay of desired transactions is still a rollback. This is how you can tell if an attempt to refute-by-redefinition is denial: first determine why it would be unfortunate if the predicate being refuted were true, and then ask if the redefinition actually fixes the problem.

[DennisP]

Ethereum didn't have to replay transactions, because there was no rollback at all; it was an isolated change to the data in one contract. Ethereum doesn't work the way Bitcoin does.

[mannykannot]

Here we have another distinction without a relevant difference. A rollback is defined by its consequences, not the details of its process.

[bringtheaction]

> Technology wise, git is as powerful as a blockchain at being an append-only log without the most important ingredient - proof-of work.

PoW is not required to have a blockchain. What you need is any consensus algorithm. For example you could use Proof of Stake.

[ufo]

The impression I got last time I studies about proof of stake is that it is still an open problem. You need to find ways to stop people from gaming the system by computing multiple parallel histories (which would devolve the system into proof-of-work) and the only ways to do this that I am aware of are at least partially reliant on agreeing on a central authority.