Since its inception, Bitcoin users had maintained a common set of rules for the cryptocurrency. On 21 July 2017, bitcoin miners locked-in a software upgrade referred to as Bitcoin Improvement Proposal (BIP) 91, which meant that the Segregated Witness upgrade would activate at block 477,120. Segwit controversially would enable second layer solutions on bitcoin such as the Lightning Network. A key difference of opinion between Bitcoin users was over the running of nodes. Bitcoin supporters wanted to keep blocks small so that nodes could be operated with less resources, while some large block supporters find it acceptable that (due to large block sizes), nodes might only be run by universities, private companies and nonprofits.