Hard fork questions

[Bernard Lerring]

What is a hard fork?

I'm assuming that it's when a collective that are trusted within the Bitcoin community get together and shut the network down temporarily in order to install a modified version of the blockchain. I'm assuming this is to correct either an error or disadvantaged situation in the blockchain or to enable it to work with a change in Bitcoin protocol. Am I right?

I've also seen that there was a hard fork back in 2012. What happened and what was the reason for doing it?

[Swordsoffreedom]

A hard fork is a change of the Bitcoin protocol that is not backwards-compatible;

The example from 2012 your mentioning is from March 2013 and was a Chain Fork which resulted in a new client that did not recognize previous Bitcoin transactions

An explanation of what happened is in this link
https://bitcoin.org/en/alert/2013-03-11-chain-fork

Simply put the reason for reverting back was that the new client was not compatible with the old one so the community decided to revert to the original chain and abandon that fork.

http://bitcoin.stackexchange.com/questions/9986/how-is-a-hard-fork-resolved

To simplify it a bit more

Miners control the network and can decide on any changes to it with the majority of mining power

Edit Found a Reddit think this is simple enough if your still a bit lost feel free to ask
http://www.reddit.com/r/Bitcoin/comments/1a51xx/now_that_its_over_the_blockchain_fork_explained/


The programs that read the blockchain, the bitcoin ledger, disagree.

Due to a bug in 0.7, it says that HIS is the correct version of this ledger and 0.8 says that HIS is the correct version.

Miners (the people who add pages to the blockchain) are told to switch to the 0.7 program so that this version gains more support and the other one is discarded. (orphaned).

Regular users are not affected. Their transactions are included in both ledgers and don't need to change any programs.

During that time, though, there is a slight chance of a double-spend ocurring. That is why people recommended merchants and exchanges to wait until there is one single blockchain again before processing purchases and merchandise.

@ In regards to op there would be two ledgers recording transactions at the same time
Both would disagree and state their version is correct and miners would make the final decision
The network does not shut down it's just that their are two chains recording the transactions and not willing to agree with each other on the outcome
This is resolved with one chain becoming longer than the other

The problem with the 2013 fork was that 0.8 and 0.7 both thought their version was correct and could not resolve the issue
This was solved with miners deciding to use 0.7 over 0.8 which then led to 0.8 accepting the changes and not disputing the transactions.

[Bernard Lerring]

Thanks. I'll read that link later.

[ShakyhandsBTCer]

Long story short, a hard-fork is when the protocol is changed as of x block

In order for this to be implemented it must be accepted by the miners.