What is the advantage of a fork over a parallel chain?

[Jet Cash]

It seems that trying to fork the Bitcoin chain creates confusion, and means that the forking alt is probably doomed to failure. To my mind, it would be easier to create a parallel chain with a new name, and include all the blocks up to a specified height. You could give it some advantages by reducing the block size and block generation time, and early adopters could profit from the faster and easier mining. You would also have a large store of "wealth" in the blockchain if you used the Bitcoin chain as a base, these asset holders would have a vested interest in its success.

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[bob123]

A fork basically is a parallel chain. When you fork off from a coin (e.g. Bitcoin) you change the source code as you wish (change blocksize, block generation time, .. ).
Then you make it public, try to get enough people who also 'believe' in your changes. You set a date (a specific Block#) from which on your chain will be live.
From this time on you have a "parallel" chain (with all blocks until block X being the same as in the original chain).
Im not sure what you exactly mean with "parallel chain" instead of forking. In this context its pretty much the same.

[cupronickel]

A fork basically is a parallel chain. When you fork off from a coin (e.g. Bitcoin) you change the source code as you wish (change blocksize, block generation time, .. ).
Then you make it public, try to get enough people who also 'believe' in your changes. You set a date (a specific Block#) from which on your chain will be live.
From this time on you have a "parallel" chain (with all blocks until block X being the same as in the original chain).
Im not sure what you exactly mean with "parallel chain" instead of forking. In this context its pretty much the same.

I think the OP is talking about whether you have the whole original ledger or not. His parallel chain would only include history up to a certain height, making the blockchain easier to manage & get quicker nodes (at least initially)

[Jet Cash]

A fork is a "Y" shaped chain, and the true Bitcoin goes off on one of the tines, and the new "coin" goes off on the other. There is then a destructive contest as both try to become the true Bitcoin. My idea of a parallel chain is to take the existing blockchain and duplicate it up to a certain height. You then run a modified version of core using that blockchain. There is no conflict or contest with the existing Bitcoin - it is a completely different entity at this point. However, all the existing Bitcoin holders have a claim on their copy transactions in the new blockchain. Therefore you have an existing store of value at the start point. That value will be negligible at first, but the "stakeholders" have a vested interest in making it a success as an altcoin. You call it by a completely different name such as ElfCoin from the Elfland (Alfheim) parallel universe in Norse mythology.

The reduced difficulty and ease of mining could make it attractive for the speculative acquisition of coins, and would provide a healthy reward for early adopters if it was adopted by a large enough group of people.

[HeRetiK]

That's pretty much what Bitcore / BTX has been doing:

https://bitcointalk.org/index.php?topic=1883902.0

They first did a 1:1 BTX:BTC airdrop with a claiming website and a predefined deadline. Once the claiming period passed, they deployed what they called a "virtual hardfork" in which each BTC address received BTX in a 1:0.5 ratio as a starting point.

A fork is a "Y" shaped chain, and the true Bitcoin goes off on one of the tines, and the new "coin" goes off on the other. There is then a destructive contest as both try to become the true Bitcoin.

[...]

This "destructive contest" was actually the main intent behind BCH and B2X. True, as far as coin distribution is concerned the difference between a hardfork and an airdrop is merely a semantic one. But not if it comes to politics.

[bob123]

A fork is a "Y" shaped chain, and the true Bitcoin goes off on one of the tines, and the new "coin" goes off on the other. There is then a destructive contest as both try to become the true Bitcoin.

There is no "Y" shape. Thats just for abstraction. There is no one chain of blocks in the "past". Each node has its own copy of the whole blockchain.
There isn't really a "contest" on which becomes the true bitcoin. Those forks only use bitcoins name to get "more established". Thats nothing more than a theft of the name.
A coin can't "go off from another". Those forks just have the same block history as btc to a specific height.

My idea of a parallel chain is to take the existing blockchain and duplicate it up to a certain height. You then run a modified version of core using that blockchain. There is no conflict or contest with the existing Bitcoin - it is a completely different entity at this point.

What you are describing here is a 'standard' fork. Every node has its own copy of the blockchain. After a certain height they run a modified version of the BTC code.
At this point a new coin has been created by a fork and is "a completely different entity".
Take BTG for example. Miner can't switch between the chains because BTG uses a different mining algorithm. The reason because miners switch between BTC and BCH is
because BCH uses the same mining algorith. And since miners are looking for the best profit they jump between those chains to get maximum profit.

[Jet Cash]

I understand the points made. Remember that Bitcoin is a virtual currency, so the blockchain is a logical sequence. If a stream hits a rock, and flows either side of it, and doesn't rejoin when it passes the rock, then you have two streams with a common source. With a bit on engineering, you can cause the two streams to rejoin and continue as one. That seems to be the ambition of some of the forkers.

If you forget the idea of a fork, and use the concept of an "air drop" as mentioned earlier, you have a great way to start a new coin. You are saying to the Bitcoin community - Here is another crypto-currency, and in order to get it started, I'm going to give everybody with unspent coins a holding in the new currency, all you have to do is to copy your blockchain and run one of our nodes with a wallet. The problem will be convincing people it's worth running the node.

Bitcoin is number 1, and is likely to remain in that position. That doesn't mean that there can't be a number 2 or even a number 1,000. I just think it shouldn't pretend to be Bitcoin, but it can be son of Bitcoin with a different name.