A distributed ledger (also called a shared ledger or distributed ledger technology or DLT) is the consensus of replicated, shared, and synchronized digital data that is geographically spread (distributed) across many sites, countries, or institutions. In contrast to a centralized database, a distributed ledger does not require a central administrator, and consequently does not have a single (central) point-of-failure.
In general, a distributed ledger requires a peer-to-peer (P2P) computer network and consensus algorithms so that the ledger is reliably replicated across distributed computer nodes (servers, clients, etc.). The most common form of distributed ledger technology is the blockchain (commonly associated with the Bitcoin cryptocurrency), which can either be on a public or private network. Infrastructure for data management is a common barrier to implementing DLT. 
In some cases, where the distributed digital information functions as an accounting journal rather than an accounting ledger, another term is used: RJT for replicated journal technology.
Distributed ledger data is typically spread across multiple nodes (computational devices) on a P2P network, where each replicates and saves an identical copy of the ledger data and updates itself independently of other nodes. The primary advantage of this distributed processing pattern is the lack of a central authority, which would constitute a single point of failure. When a ledger update transaction is broadcast to the P2P network, each distributed node processes a new update transaction independently, and then collectively all working nodes use a consensus algorithm to determine the correct copy of the updated ledger. Once a consensus has been determined, all the other nodes update themselves with the latest, correct copy of the updated ledger. Security is enforced through cryptographic keys and signatures.
In 2016, some banks tested distributed ledger systems for payments to determine their usefulness. In 2020, Axoni launched Veris, a distributed ledger platform that manages equity swap transactions. The platform, which matches and reconciles post-trade data on stock swaps, is used by BlackRock Inc., Goldman Sachs Group Inc., and Citigroup, Inc.
Distributed ledger technologies can be categorized in terms of their data structures, consensus algorithms, permissions, and whether they are mined. DLT data structure types include linear data structures (blockchains) to more complex directed acyclic graph (DAG) and hybrid data structures. DLT consensus algorithm types include proof-of-work (PoW) and proof-of-stake (PoS) algorithms and DAG consensus-building and voting algorithms. DLTs are generally either permissioned (private) or permissionless (public). PoW cryptocurrencies are generally either 'mined' or 'non-mined', where the latter typically indicates 'pre-mined' cryptocurrencies, such as XRP or IOTA. PoS cryptocurrencies do not use miners, instead usually relying on validation among owners of the cryptocurrency, such as Cardano or Solana.
Blockchains are the most common DLT type, with a 256-bit secure hash algorithm (SHA). DLTs based on DAG data structures or hybrid blockchain-DAG decrease transaction data size and transaction costs, while increasing transaction speeds compared with Bitcoin, the first cryptocurrency. Examples of DAG DLT cryptocurrencies include MIOTA (IOTA Tangle DLT) and HBAR (Hedera Hashgraph, a patented DLT).
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