Blockchain Fundamentals & Architecture Flashcards

What distinguishes a permissioned blockchain from a permissionless blockchain?

Answer: Permissioned blockchains restrict participation to approved entities, while permissionless allow anyone

Permissioned blockchains (e.g., Hyperledger Fabric) require identity verification and approval before participation, enabling enterprise use cases with privacy and compliance requirements.

What is the role of a 'full node' in a blockchain network?

Answer: It downloads, validates, and stores the entire blockchain and enforces consensus rules

Full nodes independently download every block and transaction, verify all consensus rules, and maintain a complete copy of the blockchain, making them the backbone of network security.

In blockchain terminology, what is 'block finality'?

Answer: The point at which a block is considered irreversible and cannot be reorganized out of the chain

Finality refers to the guarantee that a confirmed block will not be reversed; PoW chains have probabilistic finality while PoS chains like Ethereum can achieve economic finality through slashing.

What is the 'mempool' (memory pool) in a blockchain node?

Answer: A holding area for valid but unconfirmed transactions waiting to be included in a block

The mempool is an in-memory buffer on each node storing valid transactions that have been broadcast but not yet included in a confirmed block.

What is a 'soft fork' in the context of blockchain protocol upgrades?

Answer: A backward-compatible upgrade where old nodes still accept new blocks but may not understand new rules

A soft fork tightens consensus rules so new blocks remain valid under old rules, making the upgrade backward-compatible — old nodes don't update but continue accepting the chain.

What does 'sharding' aim to solve in blockchain architecture?

Answer: Scalability by partitioning the network so each node only processes a subset of transactions

Sharding splits the blockchain into parallel partitions (shards), each processing its own subset of transactions, so total throughput scales with the number of shards.

Which consensus mechanism do most enterprise blockchains (e.g., Hyperledger Fabric) use instead of Proof-of-Work?

Answer: Proof-of-Authority or Byzantine Fault Tolerant (BFT) variants

Enterprise chains prefer PoA or BFT-style consensus (e.g., PBFT, Raft) because known validators can reach fast, energy-efficient finality without competitive mining.