Specific questions about Blockchain : <p>I have familiarized with the blockchain technology for some time through internet research and tutorials, but, as blockchain often appears as a business topic, I could not find good answers to some technical questions. I hope, some of you could help me:</p>

<ol>
<li>The concept of blockchain says that all transaction data is stored on every node (e.g. computer) of the network. Isn’t that a huge and continuously growing amount of data every single participant should store? (If the answer is that just certain nodes have to save the whole history, wouldn’t this be in contrast to the idea of decentralization?)</li>
<li>What is the purpose for the very complex hashing procedure of Bitcoin? As far as I understand it, hashing is needed for the immutability of the chain, but why does it have to be so time-consuming as it is? On the other hand hashing is often considered as a „signature“ of the miner; what does that mean? Doesn’t signature usually mean something like a private key? </li>
<li>As blockchain is of course not bitcoin, is this complex hashing procedure also needed for other use cases (like supply chain applications…) or can it be replace by simpler hashes?</li>
<li>To protect privacy the participants of a blockchain are mostly hashed as well, which is often listed as a great advantage of the technology. In more exclusive blockchains than the bitcoin, isn’t it very simple to conclude some players through their behavior. I mean, if a very big party participates in the blockchain, it is well detectable by e.g. the frequency or volume of deals.</li>
<li>If a miner has hashed and added a block, do all the other miners instantly reject the block they currently try to create?</li>
<li>How does blockchain synchronize the transactions? In distributed systems it is always a big deal to clarify which action happened first. Some of the blockchain literature sources say that all transactions of a blockchain are first stored in a pool before adding to a block. This would be bad in e.g. auction-like deals.</li>
<li>Some sources state that a chain is considered correct when the majority (51%) of the nodes contains it. How does it work/ when is this checked? On the homepage <a href="https://medium.com/coinmonks/what-is-a-51-attack-or-double-spend-attack-aa108db63474" rel="nofollow noreferrer">https://medium.com/coinmonks/what-is-a-51-attack-or-double-spend-attack-aa108db63474</a> the 51% refer to the computational capacities and not the number of nodes and in the context of an attack…</li>
</ol>

<p>Thank you very much in advance! I will appreciate your answers.</p>
