Bitcoin Cash is a hard fork of the cryptocurrency bitcoin. The fork occurred on August 1, 2017.
On July 20, 2017, the bitcoin miners voted, 97% in favor, on the Bitcoin Improvement Proposal (BIP) 91. The proposal, by Bitmain Warranty engineer James Hilliard, was to activate Segregated Witness (SegWit). Some members of the bitcoin community felt that adopting BIP 91 without increasing the block-size limit would simply delay confronting the issue and that it favored people who wanted to treat bitcoin as a digital investment rather than as a transactional currency. They announced implementation of Bitcoin Cash as a hard fork for August 1. It inherited the transaction history of the bitcoin currency on that date, but all later transactions were separate. Block 478558 was the last common block and thus the first Bitcoin Cash block was 478559. Bitcoin Cash wallet started to reject BTC block and BTC transactions since 13:20 UTC, Aug 1st 2017 because it used a timer to initiate a fork. It implements a block size increase to 8 MB. Bitcoin Cash started futures trading at 0.5 BTC on July 23, but dropped to 0.1 BTC by July 30. Market cap appeared since 23:15 UTC, August 1, 2017. As of 30 August 2017 one Bitcoin Cash is traded at around 0.13 Bitcoin. On August 9th, it was 30% more profitable to mine on the original chain. Even though the fork allows for a higher block size, block generation was so sporadic that the original chain was 920 MB bigger than the chain of the fork, as of 9 August 2017. Due to several difficulty adjustments, the profitability of mining either chain has then switched repeatedly and as of 30 August 2017 around 1,500 more blocks were mined on the Bitcoin Cash chain than on the original one.
Response from exchanges
Coinbase initially announced that it would not support Bitcoin Cash. This led to consumer backlash and speculation about a class action lawsuit from consumers. On August 3, Coinbase announced that it would start supporting Bitcoin Cash transactions by January 1, 2018, and that users who had any amount of bitcoin at the time of the fork were credited an equal amount of Bitcoin Cash though they could start transacting in it only once Coinbase was ready to transact.
China-based ViaBTC began allowing trading in Bitcoin Cash before it went live. Kraken and Bitfinexannounced that they would support Bitcoin Cash. On August 4, 2017, Bitfinex officially opened up Bitcoin Cash deposits and withdrawals. BitMEX, Exodus, and Bitstamp announced that they would not support Bitcoin Cash. Poloniex had not announced a decision as of July 2017, but said that they were making a decision keeping the security of users' bitcoins in mind. In mid-August Poloniex began trading Bitcoin Cash.