Purplecoin

• Scalable: Purplecoin is made up of 256 shards, each representing a different blockchain that processes transactions concurrently. The average transaction size is 450 bytes, with a maximum block size of 380kb, and a production rate of 256 blocks per 30 seconds we can achieve ~12000 transactions per second on a blockchain system that has roughly the same safety guarantees as Bitcoin. Shards are processed in groups, called "shard sectors" in order to stabilise the required hashrate to successfuly attack the system.
• Decentralized & Secure: Scalability usually comes at the cost of centralization. For example Proof of Stake consensus is scalable and green but brings the security of the network in the hands of the few. Purplecoin fully uses Proof of Work, the most secure and decentralized consensus algorithm. Miners secure the network as is the case of Bitcoin
• Stateless: Nodes are not required to store all past transactions in order to validate new blocks. A miner only requires storing the latest 50 block headers of each shard, which total a size of 20mb, in order to start mining and fully validating new blocks across all shards. This means that miners and ultra-light nodes can run in memory only mode and and still be able to fully validate blocks.
• Fast Sync: Due to the stateless design, nodes without a transaction history do not have to download all of the blocks from genesis and can synchronize with the network in seconds. Furthermore, we can still validate new blocks while querying for past transactions. For comparison, synchronizing with the Bitcoin network, regardless of the number and timespan of transactions, takes several days using the same internet speed. When using a trusted bridge, there is no need to query past blocks as the bridge stores and manages the UTXO set.
• Energy Efficient: Green PoW implementation designed to reduce energy consumption from mining up to 50%

Advantages when compared to Bitcoin

• Scalable
• Schnorr signatures
• Advanced smart contracts
• Merkelized Abstract Syntax Trees
• Constant chain size
• Decentralized mining pools
• Multi-asset
• Can be mined using the CPU
• Can be mined on a smartphone via decentralized mining pools

Disadvantages when compared to Bitcoin

• If one transfer involves outputs stored on multiple shards, it requires settlement on each involved shard. Atomicity is possible only on single-shard transfers
• Since nodes are not required to store the whole UTXO set in order to validate new blocks, light-nodes have to download their balances from an external party such as a long-running archival node. In theory, there is the non-zero possibility that no node on the network will store the unspent outputs if there is no node online specifically listening for them. In practice, this will almost definitely not happen but can introduce a DOS vector for light-nodes

Advantages when compared to Ethereum v1.0

• Scalable
• Schnorr signatures
• Constant chain size
• Asynchronous smart contracts
• Re-entrancy attacks are impossible by design
• Decentralized mining pools
• Can be mined using the CPU
• Can be mined on a smartphone

Disadvantages when compared to Ethereum v1.0

• Contracts are cannot have a global state as they are encoded as input spending conditions. While this is better performance wise as it allows us to parallelise contract execution, state modeling is much harder. State can only be passed from an input to the next output.
• Contracts can only interact with contracts found in the same transaction

Advantages when compared to Ethereum v2.0

• Simple architecture, more easily provable that it is decentralized/secure
• Due to the simpler architecture, a higher number of shards is possible, which equals better scalability
• Energy efficient while not using Proof of Stake, which brings a degree of centralization as a cost to energy efficiency

Disadvantages when compared to Ethereum v2.0

• While the Green PoW mining model used in Purplecoin is 50% energy efficient, Proof of Stake is 98% energy efficient