One of the major challenges in making blockchain technology ready for mass adoption is scalability. Today most blockchains can only handle a handful of transactions per second, while payment networks like VISA support several thousand transactions per second. There are many different methods to make blockchains scale and Horizen is looking into two of those possible solutions. One of them is building a Block-DAG protocol, the other is enabling sidechains, but more on sidechains in another article.

The term DAG stands for Directed Acyclic Graph. The structure on the far left is a simple graph, made up of nodes and edges connecting the nodes. In a directed graph each connection has a direction, indicated by the arrows. A directed acyclic graph (DAG) does not allow circular relationships of nodes like the one you can see in the bottom part of the directed graph.


A block in the Block-DAG is similar to a block in a blockchain. A Block in a DAG also has a block header and contains a number of transactions, just as a block in the blockchain does. Miners mine the block, meaning they are attempting to solve a computational task through random guessing. The miner that solves the task first gets to create a block, therefore deciding on the order of transactions. This method of the network coming to a consensus on the order of transactions is the same that is used by most blockchains, namely Proof-of-Work . We will explain Proof-of-Work in more detail in the Technology Section.

The main difference is that blocks on the blockchain always reference one block (the last one), while a block in the Block-DAG can reference multiple preceding blocks. Another adjustment is needed to establish a final order within the blocks of a DAG. We also cover how establishing this order works in the technology section of our Academy.

Assuming that both types of blocks contain the same number of transactions, just by looking at the graphic below it becomes intuitive that the DAG will process more transactions in a given period of time than the blockchain does. There is more storage capacity in the Block-DAG compared to the blockchain. The DAG introduces “two-dimensionality” to the otherwise linear or one-dimensional data structure of the blockchain and is a promising approach to make decentralized networks scale. If you want to learn about Directed Acyclic Graphs in more detail feel free to check our article on them in the technology section.

DAG Blockchain DAG Blockchain


The Block-DAG uses the same consensus mechanism as a blockchain to agree on the order of events but uses a different structure to connect the individual blocks. The promise of DAG’s is to increase the throughput of a decentralized ledger from a few transactions per second to possibly thousands. Time will tell if Block-DAG technology can live up to this promise.