Are Bitcoin Block Hashes Predictable?

Does every bitcoin node store all the transactions that ever took place?

• Bitcoin transaction block is a set of transactions. Is there just one master block that all the nodes use and has all the transactions that ever took place? Does the block store the actual transactions that took place or is it just the hash? Roughly at any point the nodes takes transactions that has previously not been verified and appends them to existing transaction block and also compute proof-of-work hash. Will all transactions be eventually recorded into the ledger or it possible that some transactions aren't stored. Is the transaction block actually physically stored anywhere? If all the nodes were to down or the number of nodes reduces significantly, wouldn't the bitcoin system stop working or become weak without enough people to verify and compute hashes?

• Answer:

  Its not a bloch but a blockchain The blockchain is stored on every full node and it is currently 8GB, see http://blockchain.info/charts/blocks-size?showDataPoints=false&show_header=true&daysAverageString=1&timespan=&scale=0&address= Obviously it is not stored on a mobile client, but the standard bitcoin application downloads the full blockchain Each block in the blockchain contains the current transactions verified plus a hash of the previous block. Essentially in this hash there ist the fingerprint of every block generated since the Genesis Block (http://blockchain.info/block-height/0) The important thing is that in the blockchain you can see every transaction since the Genesis Block. Transaction might be refused by the miners who generate new blocks and use proof of work to randomly chose who can define the new block. In fact micro-payment transactions need to pay a fee otherwise they will not end in the block. If all the nodes are down bitcoin stops to work, this is self-evident If a significant number of nodes are down bitcoin becomes vulnerable to double spending, but also the incentive to mine would suddenly increase dramatically, because mining ist just a distributed way to give away the mining fee, i.e. generate new bitcoins. Therefore the system tends to heal itself.