Bitcoin Cash [BCH] is a Bitcoin Core fork from August 2017.
At block 478559, Bitcoin Cash started mining its own blockchain away from the original Bitcoin chain.
Bitcoin and Bitcoin Cash share the same genesis block, as well as all previous blocks before height 478559.
Therefore anyone who held BTC before the split automatically owned BCH after the fork.
All block and transaction hashes are also the same until the fork.
Differences Between BTC and BCH
The most notable difference between the two Bitcoin versions is the address format.
BCH addresses use a different encoding to distinguish them from BTC addresses.
For example, Satoshi Nakamoto‘s first ever address is bitcoincash:qp3wjpa3tjlj042z2wv7hahsldgwhwy0rq9sywjpyy in BCH, while it is 1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa in BTC. These two map to the same address which is the recipient of the coinbase transaction of the genesis block, therefore the very first Bitcoin’s ever mined.
There are other important differences, such as block size.
Block Size Controversy
Much of the debate held until August 2017 was about the ideal Bitcoin block size.
The Bitcoin Core team, on the other hand, believed blocks should remain limited at 1 MB but simply separate the signature data from the transaction, thus freeing space for more transactions per block.
The two groups never reached a consensus, a fact which culminated with the August 2017 fork.
A large split also happened in the Bitcoin community.
To this day the Bitcoin Core remainers do not call Bitcoin Cash Bitcoin at all, but BCash.
Bitcoin Cash fans, in turn, do not consider Bitcoin Core to be the original Bitcoin either, recognizing only BCH.
The Bitcoin.com website, owned by Roger Ver, is dedicated to Bitcoin Cash.
Bitcoin.org is the original Bitcoin Core website.
The split in the community still confuses many newbies and is generally considered to have had a short term negative effect against all Bitcoin versions. Neither Bitcoin Cash or Bitcoin SV were able to obtain full superiority and promote a flippening with Bitcoin Core. Now at least three major versions of Bitcoin exist (and at least a dozen other lesser known forks).
Bitcoin SV Fork
On November 15 2018 Bitcoin Cash itself was forked and a new Bitcoin branch was created.
The new coin was called Bitcoin SV (Satoshi Vision) and once again block size was the cause for disagreement between the Bitcoin Cash devs and the SV proponents.
The SV crew wanted a much larger block size, namely 4x as large or even unlimited block size.
Recently a 1 Gigabyte Bitcoin SV block was mined on the Bitcoin SV testnet.
Today a one gigabyte block was mined on $BSV testnet.
Took over one hour since the previous block. Imagine waiting one hour for the first confirmation.https://t.co/mpK91hp12C
— crypto.bi 🔑 (@cryptodotbi) January 26, 2020
Block Size Summary
Bitcoin Core [BTC] : 1 MB
Bitcoin Cash [BCH]: 32 MB
Bitcoin SV [BSV]: 128 MB (Unlimited block size since late 2019)