Arweave is a decentralized protocol for web storage that enables users to store data permanently on the blockchain. Its storage mechanism provides a global, permanent hard drive that offers a secure and permanent data storage solution for users and developers. The native cryptocurrency of the Arweave network is $AR, which is utilized to incentivize participants in the network. 
Sam Williams and William Jones co-founded Arweave while working on their doctoral degrees at the University of Kent. According to Williams, he thought of the idea while walking up a mountain in Scotland and brought it to Jones, who helped him with the technical details. They founded a technology company for the project, which was originally called Archain, on June 28, 2017. 
On November 6, 2019, Arweave secured $5 Million in a seed round led by Andreessen Horowitz and contributions from Union Square Ventures and Multicoin Capital. In another seed round on March 5, 2019, led by Andreessen Horowitz and participation from Coinbase Ventures, they raised a total of $8 Million. 
Initial Coin Offering (ICO)
Arweave's ICO started on June 3, 2018, and within 4 days it raised a total of USD 8,700,000 backed by Arrington XRP Capital, 1kx, Benjamin Kong, and Coefficient Ventures Grand Renfield One. At the time, the $AR token was priced at 0.73 USD, and 20.6% of the total supply was available for the round. 
Before that, Arweave held a token pre-sale event in August 2017 in which 10.8% of the initially generated token supply was sold, and two public sales were completed in May 2018 and June 2018 in which 7.1% and 1.1% of the supply was sold, respectively. The company allocated an additional 19.5% for a private sale, 2.9% for project advisors, 13% for the team (subject to a five-year lock-up with 20% released per year), 19.1% for ecosystem development, and 26.5% for future project use (subject to a five-year lock-up with 20% released per year). 
Arweave is a complementary system to the Internet, using the blockchain approach to permanently store data, which cannot be changed, and using token incentives to achieve sustainability. To achieve its decentralized storage goal and also solve current blockchain problems such as scalability, slow performance, and high transaction fees, it introduced technologies including BlockWeave, Proof of Access, Wildfire, BHL, WL, and BlockShadows. These technical points complement each other to form a solution for Arweave. 
Arweave is built on a core technology called BlockWeaves, which is structured differently from traditional blockchains e.g. Bitcoin. In a typical blockchain, blocks containing transactions are linked linearly to form a chain. However, in a BlockWeave network, a set of blocks containing data is linked to multiple previous blocks, creating more of a data structure than a chain. 
In the Arweave network, each block is linked to two prior blocks - the previous block in the chain and a block from the previous history of the blockchain, called the 'recall block'. This creates a more complex graph structure known as a block weave, rather than a linear chain. The selection of the 'recall block' is determined by the height of the previous block and the previous block's height, resulting in a deterministic approach. However, the choice of the block from the block history of the weave is unpredictable. 
Proof of Access
The consensus mechanism used by Arweave is a combination of Proof of Access (PoA) and Proof of Work (PoW). In a typical PoW system, the next block is generated based solely on the previous block, but with the PoA algorithm, data from the previous block is combined to randomly select a recall block. By taking the hash value of the current block and calculating its modulus relative to the height of the current block, a recall block can be chosen to be merged into the next block. This approach has the advantage of not requiring miners to store all the blocks that form the blockchain. 
Upgrade to SPoRA
On February 24, 2021, the Arweave network upgraded to use the Succinct Random Proofs of Access (SPoRA) consensus mechanism. It is a type of consensus mechanism and until block 633720, Arweave was running Proof of Access (PoA). Block 633719 was the last PoA block on the Arweave network before the upgrade and the first SPoRA block mined is 633720. 
This upgrade is to make data retrieval more competitive and also reduce the energy required to maintain the network. SPoRA’s architecture requires less energy to maintain, resulting not only in lower overhead for miners but in a more efficient system overall. 
The purpose of this technology is to accelerate the spread of the consensus block. Traditional blockchains are limited by the size of the block, but Arweave has developed BlockShadows to solve this issue. When a new block is created and ready to be broadcast, it broadcasts complete blocks of content along with some necessary information, which other nodes can use to create new blocks. This makes the propagation of blocks faster and more flexible.
Wallet List (WL) and Block Hash List (BHL)
Nodes can perform crucial network functions without owning the entire chain with the help of two critical concepts: Block Hash List (BHL) and Wallet List (WL). BHL is a list of hashes for all previous blocks, while WL is a list of active wallets in the system. This allows users to verify trades without occupying blocks used in the previous trade. With blockchain lists and wallet lists synchronized by the network and downloadable by miners, nodes can join the network and participate almost instantly. 
Arweave developed a self-organizing network analysis and ranking system called Wildfire. Arweave is a data storage system that can hold a large amount of information and provide convenient access to it. To simplify data sharing, Wildfire adds a layer of incentives to encourage miners to share data freely. This ensures that miners are motivated to store and share data as quickly as possible with other miners in the network, which in turn earns them a positive reputation. Wildfire creates a ranking system locally on each node, where each peer is ranked by its performance, and the overall network blacklists poorly performing peers. 
The Arweave protocol offers a blacklist system that grants nodes the freedom to select the content they want to store. This system allows any node to blacklist any content that an individual or group of nodes may want to reject. For instance, they can blacklist the hash or string of some data they do not wish to store. Any matching disk content will never be written. When more than half of the network rejects a particular content, it is rejected across the entire network. These blacklists can be created individually or collaboratively, or imported from other sources. 
In January 2019, Arweave launched PermaWeb, a new form of web or internet. Arweave describes the Permaweb as:
“… a global, community-owned web that anyone can contribute to or get paid to maintain."
The PermaWeb offers incentivization and information permanence across a globally distributed and serverless network. It’s the web that users can use and run. It looks just like the traditional web but the difference is anything published on the PermaWeb is available forever. Everything that gets put onto Arweave needs to be paid with the AR token. This is also what the miners receive for hosting the data on their servers. 
The PermaWeb enables users to store information and build websites that live forever on a smart blockchain. As the Arweave network itself is skeptical about its contents, the PermaWeb can be used to store all kinds of information -- from wikis to PDFs, to videos, and web applications. Once included in the network, these files are always accessible, from any place in the world, at any time. Further, once submitted nobody (including their original uploader) can alter them in any way enforcing consumer integrity for applications, and verifiability for documents. 
The AR token is the native token for the Arweave platform. The token’s main unit is the AR, with sub-unit Winston, where 1 AR = 1,000,000,000,000 Winstons. Arweave Token (AR) has a total supply of 66,000,000 AR. 55 million AR were created in the genesis block at the network launch on June 8, 2018. 
The $AR tokens serve as payment for storing information on the system. These payments are rewarded to miners who participate in information storage and maintenance. The token also serves as a means of exchange for value. In order for a transaction to be carried out on a block, a user must pay a transaction fee in AR. Unlike traditional blockchain systems, this transaction fee is not directly transferred to the miner of the block. Instead, most of the transaction fee is allocated to a storage endowment, which is gradually distributed to the wallets of miners over time. 
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