Are all Blockchains decentralised?

Not all blockchains are decentralized. While decentralization is a core feature of many blockchain networks, there are also variations in the level of decentralization across different blockchain implementations. Here are the main categories:

1. Decentralized Blockchains: These are fully decentralized networks where no single entity or group controls the majority of nodes or mining power. Examples include Bitcoin and Ethereum (though Ethereum is in the process of transitioning to a more decentralized model with Ethereum 2.0). In these networks, anyone can participate as a node and contribute to the consensus process.

2. Partially Decentralized Blockchains: Some blockchain networks may have elements of decentralization but still rely on a certain degree of centralization in certain aspects. For example, permissioned blockchains may have a set of trusted nodes or validators who are responsible for validating transactions, which can introduce some level of centralization.

3. Centralized Blockchains: In some cases, blockchain networks may be centralized, meaning that control over the network is concentrated in the hands of a single entity or a small group of entities. These networks may not offer the same level of censorship resistance or trustlessness as decentralized networks. Examples include some private or consortium blockchains used by enterprises.

It's important to consider the decentralization aspect when evaluating different blockchain projects, as it can have implications for security, censorship resistance, and overall trust in the network.