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Core Protocol

SIMD (Solana Improvement Document)

A formal specification document describing proposed and accepted changes to the Solana protocol, analogous to Ethereum's EIPs. SIMDs are categorized as Standard (Core, Networking, Interface) or Meta, and require supermajority validator stake-weighted voting (66.67%) to pass. Notable SIMDs include SIMD-33 (Timely Vote Credits), SIMD-123 (Block Revenue Sharing), SIMD-228 (Market-Based Emissions), and SIMD-326 (Alpenglow).

IDsimdAliasSolana Improvement Document
Plain meaning

Plain meaning

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A formal specification document describing proposed and accepted changes to the Solana protocol, analogous to Ethereum's EIPs. SIMDs are categorized as Standard (Core, Networking, Interface) or Meta, and require supermajority validator stake-weighted voting (66.67%) to pass. Notable SIMDs include SIMD-33 (Timely Vote Credits), SIMD-123 (Block Revenue Sharing), SIMD-228 (Market-Based Emissions), and SIMD-326 (Alpenglow).

Mental model

Mental model

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Technical context

Technical context

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Consensus, leader rotation, slots, epochs, and the runtime.

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Why builders care

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SIMD (Solana Improvement Document) (simd)
Category: Core Protocol
Definition: A formal specification document describing proposed and accepted changes to the Solana protocol, analogous to Ethereum's EIPs. SIMDs are categorized as Standard (Core, Networking, Interface) or Meta, and require supermajority validator stake-weighted voting (66.67%) to pass. Notable SIMDs include SIMD-33 (Timely Vote Credits), SIMD-123 (Block Revenue Sharing), SIMD-228 (Market-Based Emissions), and SIMD-326 (Alpenglow).
Aliases: Solana Improvement Document
Related: Validator, Consensus Mechanism, Epoch
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Branch

Validator

A node that participates in the Solana network by validating transactions, voting on blocks, and (when selected as leader) producing new blocks. Validators run the Agave, Firedancer, or Jito client software, require significant hardware (128+ GB RAM, high-core CPU, NVMe SSD), and earn rewards from inflation and transaction fees.

Vote AccountStake
Open term
Branch

Consensus Mechanism

The protocol by which nodes in a distributed network agree on the current state of the ledger. Common mechanisms include Proof of Work (Bitcoin), Proof of Stake (Ethereum, Solana), and BFT variants. Consensus ensures all honest nodes converge on the same transaction history despite potential network delays or malicious actors.

Proof of Stake (PoS)Proof of Work (PoW)
Open term
Branch

Epoch

A period of 432,000 slots (approximately 2-3 days) that defines a staking cycle. At each epoch boundary, the leader schedule is recalculated based on stake weights, stake activations/deactivations take effect, and inflation rewards are distributed to validators and delegators.

SlotLeader Schedule
Open term
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Core Protocol

Validator

A node that participates in the Solana network by validating transactions, voting on blocks, and (when selected as leader) producing new blocks. Validators run the Agave, Firedancer, or Jito client software, require significant hardware (128+ GB RAM, high-core CPU, NVMe SSD), and earn rewards from inflation and transaction fees.

Open term
Blockchain General

Consensus Mechanism

The protocol by which nodes in a distributed network agree on the current state of the ledger. Common mechanisms include Proof of Work (Bitcoin), Proof of Stake (Ethereum, Solana), and BFT variants. Consensus ensures all honest nodes converge on the same transaction history despite potential network delays or malicious actors.

Open term
Core Protocol

Epoch

A period of 432,000 slots (approximately 2-3 days) that defines a staking cycle. At each epoch boundary, the leader schedule is recalculated based on stake weights, stake activations/deactivations take effect, and inflation rewards are distributed to validators and delegators.

Open term
Core Protocol

SIMD-123 (Block Revenue Sharing)

A protocol change enabling validators to automatically share block revenue (priority fees and MEV tips) with their delegators through an on-chain mechanism. Validators set a commission rate for block revenue, and the protocol distributes the remainder to delegators at epoch boundaries based on their stake proportion. Available in Agave 3.0+.

Open term
Commonly confused with

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Core Protocolsimd-123

SIMD-123 (Block Revenue Sharing)

A protocol change enabling validators to automatically share block revenue (priority fees and MEV tips) with their delegators through an on-chain mechanism. Validators set a commission rate for block revenue, and the protocol distributes the remainder to delegators at epoch boundaries based on their stake proportion. Available in Agave 3.0+.

AliasBlock Revenue Sharing
Open term
Related terms

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Core Protocolvalidator

Validator

A node that participates in the Solana network by validating transactions, voting on blocks, and (when selected as leader) producing new blocks. Validators run the Agave, Firedancer, or Jito client software, require significant hardware (128+ GB RAM, high-core CPU, NVMe SSD), and earn rewards from inflation and transaction fees.

Open term
Blockchain Generalconsensus

Consensus Mechanism

The protocol by which nodes in a distributed network agree on the current state of the ledger. Common mechanisms include Proof of Work (Bitcoin), Proof of Stake (Ethereum, Solana), and BFT variants. Consensus ensures all honest nodes converge on the same transaction history despite potential network delays or malicious actors.

Open term
Core Protocolepoch

Epoch

A period of 432,000 slots (approximately 2-3 days) that defines a staking cycle. At each epoch boundary, the leader schedule is recalculated based on stake weights, stake activations/deactivations take effect, and inflation rewards are distributed to validators and delegators.

Open term
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Core Protocol

Proof of History (PoH)

A clock mechanism that cryptographically proves the passage of time between events. PoH uses a sequential SHA-256 hash chain where each output becomes the next input, creating a verifiable ordering of events without requiring consensus. The leader produces ~400,000 hashes per slot (~400ms), and any validator can verify the sequence in parallel, enabling Solana's high throughput by removing the need for validators to agree on time.

Open term
Core Protocol

Tower BFT

Solana's custom BFT consensus algorithm built on top of Proof of History. Tower BFT uses PoH as a clock to reduce communication overhead in traditional PBFT from O(n²) to O(n). Validators vote on forks with exponentially increasing lockout periods—each consecutive vote doubles the lockout, making rollbacks progressively more expensive. A fork is finalized when it reaches supermajority (66.7%+ of stake).

Open term
Core Protocol

Slot

A time window during which a designated leader validator can produce a block. Each slot lasts approximately 400 milliseconds. Slots are numbered sequentially from genesis and grouped into epochs of 432,000 slots (~2-3 days). Not every slot produces a block—a skipped slot means the leader was offline or too slow.

Open term
Core Protocol

Block

A set of entries produced by a leader during a single slot. A block contains transactions bundled into entries, each with a PoH hash proving ordering. Blocks are broken into shreds for network propagation via Turbine. Maximum block size is limited by compute units (48M CU cap per block) rather than byte size.

Open term