Blockchain Technology

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The most widely recognized Implementation of the blockchain technology is Bitcoin. Bitcoin was also the first truly decentralized digital currency. Bitcoin functions as a P2P system, providing people with the means to transfer value digitally and directly.  In January 2009, the bitcoin network came into existence with the release of the first open source bitcoin client and the the first bitcoins were issued, with Satoshi Nakamoto mining the first block of bitcoins ever (known as the genesis block), which had a reward of 50 bitcoins.

Ethereum was proposed in late 2013 by Vitalik Buterin, a cryptocurrency researcher and programmer. Development was funded by an online crowdsale that took place between July and August 2014. The system went live on 30 July 2015, with 11.9 million coins "premined" for the crowdsale. This accounts for approximately 13 percent of the total circulating supply.

Ethereum is an open-source, public, blockchain-based distributed computing platform featuring smart contract (scripting) functionality. Ether is a cryptocurrency whose blockchain is maintained by the Ethereum platform, which provides a distributed ledger for transactions. Ether can be transferred between accounts and used to compensate participant nodes for computations performed. Ethereum provides a decentralized Turing-complete virtual machine, the Ethereum Virtual Machine (EVM), which can execute scripts using an international network of public nodes. "Gas", an internal transaction pricing mechanism, is used to mitigate spam and allocate resources on the network.

An Ethereum Distributed App is an application where the “server side” is just one or more Smart Contracts that exist on the Ethereum network.

A Distributed Application doesn’t have to store all the current state or perform all of its compute work on the blockchain, this could be very expensive for end-users. The distributed app does eventually store trusted read state on the Ethereum blockchain.

Distributed applications are usually accompanied by a user-friendly front end application because to do manual transactions to & from contracts using a CLI would be a lot of work. 

Ethereum “Smart Contract” stores some state on a blockchain.  A state, can point to an integer that is stored in a map of Ethereum addresses we can call it a Token balance.