Decentralized applications don't necessarily need to run on top of a blockchain network. Tor, BitTorrent, Popcorn Time, BitMessage, are examples for decentralized applications that run on a P2P network, but not on a blockchain – which is a special kind of P2P network.
Decentralized applications are a piece of so ware that communicates with the blockchain, which manages the state of all network actors. The interface of the decentralized applications does not look any different than any website or mobile app today. The smart contract represents the core logic of a decentralized application. Smart contracts are integral building blocks of blockchains, that process information from external sensors or events and help the blockchain manage the state of all network actors.

The frontend of a decentralized application represents what you see, and the backend represents the entire business logic. This business logic is represented by one or several smart contracts interacting with the underlying blockchain. The frontend, as well as files like a photo, a video, or audio, could be hosted on decentralized storage networks such as Swarm or IPFS. Traditional Web applications use HTML, CSS, and javascript or the like to render a webpage. This page interacts with a centralized database, where all the data is stored. When you use a service like Twitter, Facebook, Amazon, or Airbnb, for example, the webpage will call an API to process your personal data and other necessary information stored on their servers, to display them on the page. User ID and passwords are used for identification and authentication, with low levels of security, since personalized data is stored on the server of the service provider.

Decentralized applications are similar to a traditional Web application. The frontend uses the exact same technology to render the page. It contains a "wallet" that communicates with the blockchain. The wallet manages cryptographic keys and the blockchain address. Public-key infrastructure is used for user identification and authentication. Instead of an API connecting to a database, a wallet so – ware triggers activities of a smart contract, which interacts with a blockchain.

In contrast to Web2 applications, Web3 applications need a connection to the blockchain, which is managed by a special application called "wallet." It keeps a record of the private keys and blockchain address, which represents the unique 30 identities and point of reference. Without a so ware that manages our digital identity, we will not be able to interact with the blockchain. The Web3, therefore, builds on the current Web2 stack and introduces additional elements on an application level. In the backend, the Web3 adds a whole new infrastructure layer for decentralized applications to interact with – the decentralized protocol stack. Decentralized apps need to have a component that manages a user's private keys, with which one can sign transactions on the state layer, the blockchain.
On smart contracts
To introduce dapps, we need to introduce smart contracts – a dapp's backend for lack of a better term. For a detailed overview, head to our section on smart contracts.
A smart contract is code that lives on the Ethereum blockchain and runs exactly as programmed. Once smart contracts are deployed on the network you can't change them. Dapps can be decentralized because they are controlled by the logic written into the contract, not an individual or company. This also means you need to design your contracts very carefully and test them thoroughly.
BENEFITS OF DAPP DEVELOPMENT
Zero downtime – Once the smart contract is deployed and on the blockchain, the network as a whole will always be able to serve clients looking to interact with the contract. Malicious actors, therefore, cannot launch denial-of-service attacks targeted towards individual dapps.
Privacy – You don't need to provide real-world identity to deploy or interact with a dapp.
Resistance to censorship – No single entity on the network can block users from submitting transactions, deploying dapps, or reading data from the blockchain.
Complete data integrity – Data stored on the blockchain is immutable and indisputable, thanks to cryptographic primitives. Malicious actors cannot forge transactions or other data that has already been made public. Trustless computation/verifiable behavior – smart contracts can be analyzed and are guaranteed to execute in predictable ways, without the need to trust a central authority. This is not true in traditional models; for example, when we use online banking systems, we must trust that financial institutions will not misuse our financial data, tamper with records, or get hacked.

DRAWBACKS OF DAPP DEVELOPMENT
Maintenance – Dapps can be harder to maintain because the code and data published to the blockchain are harder to modify. It's hard for developers to make updates to their dapps (or the underlying data stored by a dapp) once they are deployed - even if bugs or security risks are identified in an old version.
Performance overhead – There is a huge performance overhead, and scaling is really hard. To achieve the level of security, integrity, transparency, and reliability that Ethereum aspires to, every node runs and stores every transaction. On top of this, proof-of-work takes time as well. A back-of-the-envelope calculation puts the overhead at something like 1,000,000x that of standard computation currently.
Network congestion – When one dapp uses too many computational resources, the entire network gets backed up. Currently, the network can only process about 10-15 transactions per second; if transactions are being sent in faster than this, the pool of unconfirmed transactions can quickly balloon.
User experience – It may be harder to engineer user-friendly experiences because the average end-user might find it too difficult to set up a tool stack necessary to interact with the blockchain in a truly secure fashion. Centralization – User-friendly and developer-friendly solutions built on top of the base layer of Ethereum might end up looking like centralized services anyways. For example, such services may store keys or other sensitive information server-side, serve a frontend using a centralized server, or run important business logic on a centralized server before writing to the blockchain. Centralization eliminates many (if not all) of the advantages of blockchain over the traditional model.
What is Ethereum?

To understand what a Dapp is, you first need to understand what Ethereum is. Now, there are other protocols that are used to build Dapps, like EOS, NEO, Stellar, Tron, and Cardano, but the big dog is Ethereum.
Ethereum is a network protocol that allows users to create and run smart contracts over a decentralized network. A smart contract contains code that runs specific operations and interacts with other smart contracts, which has to be written by a developer. Unlike Bitcoin which stores a number, Ethereum stores executable code.
So, why should you care?

Because Ethereum removes the need for a third party to handle transactions between peers. Since the middle man is replaced by code, all kinds of costs are reduced, including time and money.
Just like Bitcoin removes the need for someone to hold your money, Ethereum removes the need for someone to broker a deal.
Now you might be wondering, where are all these smart contracts? Well, they're essentially hosted on multiple computer nodes all across the world.
These nodes contain all of the information of all the world's smart contracts, including code, transactions, etc. They're constantly working to keep this information up-to-date so they all have the exact same copy. This what makes smart contracts, and cryptocurrencies in general, decentralized.
And since all of the nodes have the same information and are spread across the world, the removal of a node won't interrupt the execution of any smart contract. Redundancy ensures uptime. Ethereum Dapps: The Backbone of Web 3.0
Since the creation of the Internet, the amount of information and human interaction has exploded. We're able to produce and consume information at near infinite levels.
Unfortunately, the ability to control this information has become heavily centralized over time. This includes information about your social life, health, finances, and much more. Those who control this information are the ultimate owners of it and can use it as they see fit.
These are essentially middle men that hold your information on their centralized servers so they can provide you with services, like holding your money, hosting you website, connecting with family and friends, etc. And at the push of a button, they can completely remove you from accessing this (your?) information and all related services.
This is a monopoly on the information you produce and consume as well as the services you use. Thankfully, Web 3.0 changes all of that and Ethereum Dapps are playing a central role.
Web 3.0 is a lot of things, but at its core is a technology based on decentralization. By decentralizing information and services, large corporations and governments won't be able to control users of the Internet through monopolistic, authoritarian tactics.
Ethereum Dapps, with their ability to decentralize information and services, gives Web 3.0 a platform to deliver a completely free (as in freedom) and accessible Internet for everyone. No longer will there be a central point of control because there won't be middle men to facilitate the flow of information and services.
Some of the most promising Ethereum tokens and Dapps are laying the foundation for the future of the Internet, including:
Basic Attention Token (BAT): used to improve privacy and value transfer between users, publishers, and advertisers. Used in the Brave browser.
Golem (GNT): used to run code on one or many distributed compute nodes.
Minds: a social media platform that improves value transfer between content creators and consumers.
TokenSets: used to manage cryptocurrency assets via tokenized automated asset management strategies.
Aave: used to earn interest on cryptocurrency deposits and borrow cryptocurrency assets.
IDEX: a decentralized cryptocurrency exchange.
Since the creation of Bitcoin, the first cryptocurrency, there's been a massive growth in the cryptoverse.
Being able to store data in a decentralized way was a necessary stepping stone to the decentralization of code execution. With Ethereum, it's now possible to deploy smart contracts across the world to power the backend for existing and future Dapps.
And as more and more Dapps are launched, we'll get closer and closer to a more free, fair, and accessible Internet.

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