Recently people at various events started asking us what is the difference between DLT and Blockchain. Most of the new startups are now adding more buzzwords and change word Blockchain to DLT. However, the interesting thing is, what is what?

Let's start with definitions:

Blockchain is a network of computers having an identical copy of the database (list of transactions) and changing its state by a common agreement based on pure mathematics and cryptography. There is no need for any central server or agent to trust to (due to the shared database between network participants). Transactions are put in blocks at a certain period, hashed and confirmed by nodes in the network. As a result, we have a chain of blocks, where each block points to the previous block hash. And due to the chain structure, we achieve a tamperproof storage.

is a network of computers having an identical copy of the database (list of transactions) and changing its state by a common agreement based on pure mathematics and cryptography. There is no need for any central server or agent to trust to (due to the shared database between network participants). Transactions are put in blocks at a certain period, hashed and confirmed by nodes in the network. As a result, we have a chain of blocks, where each block points to the previous block hash. And due to the chain structure, we achieve a tamperproof storage. Distributed Ledger Technology (DLT) is a consensus of replicated, shared, and synchronised digital data geographically spread across multiple sites, countries, or institutions. There is no central administrator or centralised data storage. A peer-to-peer network is required as well as consensus algorithms to ensure replication across nodes is undertaken.

Both of the definitions seems to be similar.

But what is the difference?

One form of distributed ledger design is the blockchain system. Blockchain goes under the DLT definition and is just one type of distributed ledger.

DLT is a broader term that does not limit the definition to the structure of blocks and chains. Data structures in the DLT can vary and algorithms used to reach the same goal (shared ledger) can be achieved in various ways:

Blockchain . Using different consensus algorithms (e.g. proof of work) transactions are verified and put into blocks by the network nodes. Examples: Bitcoin, Ethereum, Hyperledger.

. Using different consensus algorithms (e.g. proof of work) transactions are verified and put into blocks by the network nodes. Examples: Bitcoin, Ethereum, Hyperledger. Directed Acyclic Graph (DAG) / Tangle . The key idea behind is that the previous transaction validates the succeeding transaction to achieve the consensus. The core innovation behind using a DAG is its ability to have zero-fee transactions. The Tangle, in particular, removes miners by making validation of transactions an intrinsic part of the ledger — making miners (nodes confirming transactions) and people sending transactions one and the same. The self-regulating Tangle Network only requires two confirmations per transaction. In doing so, much less computing power is needed, and thus, much less electricity. DAG doesn't need to link large blocks one after another in a long chain. Rather, it is building a graph of transactions. Examples: IOTA tangle, Byteball, Nano.

. The key idea behind is that the previous transaction validates the succeeding transaction to achieve the consensus. The core innovation behind using a DAG is its ability to have zero-fee transactions. The Tangle, in particular, removes miners by making validation of transactions an intrinsic part of the ledger — making miners (nodes confirming transactions) and people sending transactions one and the same. The self-regulating Tangle Network only requires two confirmations per transaction. In doing so, much less computing power is needed, and thus, much less electricity. DAG doesn't need to link large blocks one after another in a long chain. Rather, it is building a graph of transactions. Examples: IOTA tangle, Byteball, Nano. Hashgraph . Nodes are creating consensus through virtual voting. It does not need miners to validate transactions and uses directed acyclic graphs for time-sequencing transactions without bundling them into blocks. At the end of each round (period), each node calculates the shared state after processing all transactions that were received in that round and before, and it digitally signs a hash of that shared state, puts it in a transaction, and gossips it out to the community. Using a gossip protocol, nodes efficiently and rapidly exchange data with other nodes in the community. This automatically builds a hashgraph data structure using the novel “gossip about gossip” protocol. This data structure is cryptographically secure and contains the history of communication in a community. Using this as an input, nodes run the same virtual-voting consensus algorithm as other nodes. The community reaches consensus on the order and timestamp without any further communication over the internet. Each event is digitally signed by its creator. Examples: Hedera Hashgraph.

. Nodes are creating consensus through virtual voting. It does not need miners to validate transactions and uses directed acyclic graphs for time-sequencing transactions without bundling them into blocks. At the end of each round (period), each node calculates the shared state after processing all transactions that were received in that round and before, and it digitally signs a hash of that shared state, puts it in a transaction, and gossips it out to the community. Using a gossip protocol, nodes efficiently and rapidly exchange data with other nodes in the community. This automatically builds a hashgraph data structure using the novel “gossip about gossip” protocol. This data structure is cryptographically secure and contains the history of communication in a community. Using this as an input, nodes run the same virtual-voting consensus algorithm as other nodes. The community reaches consensus on the order and timestamp without any further communication over the internet. Each event is digitally signed by its creator. Examples: Hedera Hashgraph. Holochain. An energy efficient post-blockchain ledger system and decentralized application platform that uses peer-to-peer networking for processing agent-centric agreement and consensus systems. The key advantage of Holochain is that every device on the network gets its own secure ledger and can function independently while also interacting with all the other devices on the network for a truly decentralized edge computing solution. The interesting thing is that there is no overall, global "correctness" (or consensus) built into Holochain. Instead, each node that receives a record of a transaction validates it against the shared application rules and gossips it to their peers. If the rules are broken, that transaction is rejected by the validator. Example: Holochain.

Therefore, Blockchain is just one type of DLT and there are many different technologies being developed to reach the similar goal by solving issues of existing Blockchain solutions (scalability, security, speed).

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Sources: hedera.com, holochain.org, hackernoon.com/wtf-is-holochain-35f9dd8e5908, 101blockchains.com/blockchain-vs-hashgraph-vs-dag-vs-holochain/