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it is like mining where does the free block rewards come from

so is steem minable?

no its a comparison , bitcoin generates new bitcoin with mining, steem generates new steem for upvotes

So the more Steem power you have the more Hashpower you have like for mining

Steemit doesn’t have ‘Miners’ It has ‘Witnesses’

Unlike bitcoins, Steemit is based on a blockchain technology called ‘Graphene’ which uses ‘Witness’ for producing Steem coin blocks. When a Steem Block is witnessed 10%of it goes to the witness and the rest 90 % is awarded to the content creators and curators and the users with STEEM Power. 21 witness nodes are produced every 63 second by 21 witnesses, There are 20 of them and they might change based on the number of votes they receive.
@utfull @topslim