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The main disadvantages are huge expenditures, “uselessness” of computations and 51 percent attack.

Contracts can call other contracts or send Ether to non-contract accounts by the means of message calls. Message calls are similar to transactions, in that they have a source, a target, data payload, Ether, gas and return data. In fact, every transaction consists of a top-level message call which in turn can create further message calls.

At the time of writing these lines, the Ethereum Blockchain still runs on Proof of Work. When a block is mined, the miner node selects some transactions from a pool of pending transactions. Usually they are sorted by how much gas they would bring in. These transactions are executed and incorporated in the new block. But a block also contains two very important parameters: a difficulty and a timestamp. The difficulty regulates how hard it is to find a block by the miner. The mining time is set to be between 10 and 20 seconds. If it’s beyond 20 seconds, the difficulty is too high and will be automatically lowered going forward. If the mining happens below 10 seconds, then the difficulty increases. The timestamp is the time when a miner found the block. It is not automatically derived, rather it is set by the miner itself and can thus be influenced to a certain degree. The timestamp does not depend on the time zone, as it’s the standard Unix timestamp.

Provenance means recording the history of data, from its inception to various stages of the data lifecycle. Provenance provides a detailed record of how the data was collected, where it was stored and how it is used. Blockchain holds complete provenance details of each component of data transfer. It is accessible to all the participants in a business network. It improves the system utilization and increases trust.

2.0 Ethereum came after Bitcoin. Vitalik Buterin, one of the writers for Bitcoin Magazine that tried to popularize the technology in the early 2012. He witnessed first-hand the problems in the Bitcoin implementation like wasteful mining hardware, centralized mining community, and lack of network scalability. In 2013, the then 19 year old Vitalik described his vision for Ethereum by extending the concept of Bitcoin beyond just currency. He proposed a platform where developer community and entrepreneurs to build distributed application (Dapps) for the Blockchain network. He referred to this concept of trust beyond just currency as ‘smart contracts’ or even blockchain-based “decentralized autonomous organizations” (DAOs).

Gas is supposed to be the constant cost of network resources/utilization. You want the real cost of sending a transaction to always be the same, so you can’t really expect Gas to be issued, currencies in general are volatile. So instead, we issue ether whose value is supposed to vary, but also implement a Gas Price in terms of Ether. If the price of ether goes up, the Gas Price in terms of ether should go down to keep the real cost of Gas the same.

Calls are limited to a depth of 1024, which means that for more complex operations, loops should be preferred over recursive calls.

The ledger system in Hyperledger fabric uses levelDB. By definition, LevelDB allows concurrent writers to safely insert data into the database by providing internal synchronization. LevelDB uses very coarse-grained synchronization which forces all writes to proceed in an ordered, first-come-first-served basis, effectively reduces throughput to a single thread. State database options include LevelDB and CouchDB. LevelDB is the default key-value state database embedded in the peer process. CouchDB is an optional alternative external state database. Like the LevelDB key-value store, CouchDB can store any binary data that is modeled in chaincode (CouchDB attachment functionality is used internally for non-JSON binary data). But as a JSON document store, CouchDB additionally enables rich query against the chaincode data, when chaincode values (e.g. assets) are modeled as JSON data.

Docker provides a secured, lightweight method to sandbox chaincode execution that is "locked down" Chaincode Services uses Docker to host (deploy) the chaincode without relying on any virtual machine or computer language. Docker provides a secured, lightweight method to sandbox chaincode execution. The environment is a "locked down" and secured container, along with a set of signed base images containing secure OS and chaincode language, runtime and SDK images for Golang Additional programming languages can be enabled