“Amit Goel is the Founder & Chief Strategy & Innovation Officer for MEDICI. Amit’s vision is to build a strong FinTech market network that involves financial institutions, banks, startups, investors, analysts & other key stakeholders across the ecosystem – helping each one of them in a meaningful way by removing the asymmetry of information and providing a platform to engage & transact.\ \ Amit is passionate about bringing actionable FinTech-focused insights, innovative products & services for the FinTech ecosystem. Some of his work involves startup scores, bank scores/assessments, predictive viewpoints & other innovations that have helped MEDICI’s customers and the ecosystem. He has been named amongst the Top 100 FinTech thought leaders/influencers in the world & Top 10 in Asia multiple times by reputed agencies, consulting firms as well as financial institutions. Amit has built MEDICI (formerly LTP) as a new-age, tech-enabled advisory/research firm, which is now considered the #1 global research & innovation platform for FinTech in the world.\ \ Amit has been writing pioneering viewpoints on financial technology space that have been ahead of the curve since 2010. His data-driven predictions have helped the customers as well as the ecosystem. His past work experience includes a strong background in strategy & market analysis and advisory to clients (from big business houses to Fortune 500 firms) in payments, commerce, financial services & IT/technology. In the past, Amit had also founded a successful consulting & research practice called GrowthPraxis and has worked at Boston Analytics, Frost & Sullivan, and Daimler Chrysler in strategy & research.”
Bitcoin’s block interval is ten minutes so it takes about five ten minutes on average for a new transaction to find its way into a block, even if it pays a high fee. This is too slow for some people so they have experimented with alternative cryptocurrencies, based on the Bitcoin code-base, which employ quicker block intervals   [UPDATED 2014-10-27 to correct my embarrassing misunderstanding of mathematics…]
For example, Banks A and B often settle thousands of transactions per day. It would be extremely expensive for all of those transactions to be committed to the main blockchain, so A and B set up a side-chain. At the end of each day, at most one transaction is committed to the main blockchain (the only possible outcomes are A and B's balances remain the same, or one of their balances decreases and the other's increases).

^ Jump up to: a b c d e f g h i j k l "Blockchains: The great chain of being sure about things". The Economist. 31 October 2015. Archived from the original on 3 July 2016. Retrieved 18 June 2016. The technology behind bitcoin lets people who do not know or trust each other build a dependable ledger. This has implications far beyond the crypto currency.
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"I see quite a few use cases for private blockchains, and they definitely have their place. Traditional institutions won't switch to a completely public blockchain from one day to the other. A private blockchain is a great first step towards a more cryptographic future. The biggest advantages of private blockchains in comparison to centralized databases are the cryptographic auditing and known identities. Nobody can tamper with the data, and mistakes can be traced back. In comparison to a public blockchain it is much faster, cheaper and respects the company's privacy. As a conclusion, it's better to rely on a private blockchain than no cryptographic system at all. It has merits and pushes the blockchain terminology into the corporate world, making truly public blockchains a bit more likely for the future." 
Sidechains are responsible for their own security. If there isn’t enough mining power to secure a sidechain, it could be hacked. Since each sidechain is independent, if it is hacked or compromised, the damage will be contained within that chain and won’t affect the main chain. Conversely, should the main chain become compromised, the sidechain can still operate, but the peg will lose most of its value.

A side-chain is a secondary blockchain layer designed to facilitate lower-cost and/or higher-speed transactions between two or more parties. One case in which they're often deployed is between parties who make many transactions amongst each other. Committing all of those transactions to the public blockchain would may undesirable for cost or other reasons, so the side-chain's job in this example would be to aggregate the activity into the least transactional activity necessary to reflect the final state of the side-chain's ledger.
The problem with Ethereum is that transactions are executed one after another. However, Aelf differs in its parallel computing blockchain capability. It scales transaction computing power inside a single side chain. Now imagine the power when you have thousands of side chains. For any unrelated transactions, it is safe to execute them concurrently.

“Blockchain could significantly reduce time delays and human mistakes, and monitor cost, labor, waste and emissions at every point in the supply chain. In the food sector, a manufacturer could automatically identify contaminated products in a matter of seconds and wouldn’t need to pull an entire product line from store shelves in the case of contamination.”
Mastercoin and Counterparty are embedded consensus protocols (or meta-protocols) that use the blockchain to store their transactional data. Bitcoin devs, except Peter Todd who was hired by both teams to help them find a proper solution, are very unhappy, to say mildly, about storing the data on the blockchain. Heated discussions on this topic go on for hundreds of pages on bitcointalk and Mastercoin github issue. Mining pools like Eligius started censoring Mastercoin transactions (not sure if they are continuing with this practice right now, but the operators of this pool are adamant that data do not belong to the blockchain).
A private blockchain network requires an invitation and must be validated by either the network starter or by a set of rules put in place by the network starter. Businesses who set up a private blockchain, will generally set up a permissioned network. This places restrictions on who is allowed to participate in the network, and only in certain transactions. Participants need to obtain an invitation or permission to join. The access control mechanism could vary: existing participants could decide future entrants; a regulatory authority could issue licenses for participation; or a consortium could make the decisions instead. Once an entity has joined the network, it will play a role in maintaining the blockchain in a decentralized manner.