Slot (Cardano)

The smallest time period in the Cardano blockchain.

What Is a Slot (Cardano)?

A slot is the smallest time period in a blockchain. For Cardano, the slot duration is one 1 second. Each slot has a slot leader, who has the right to create a single block for that slot and can choose not to do so. If the slot leader does not create a block, there are two consequences: firstly, no blocks are created by anyone in that slot; secondly, the next slot leader will be chosen from a different staking pool than would otherwise have been the case.
Cardano’s proof-of-stake protocol is based on a system of epochs and slots.  
Each Cardano epoch consists of slots with each slot lasting for one second. A Cardano epoch currently includes 432,000 slots (5 days). In the Byron era, which was the genesis of Cardano, and is now replaced by Shelley mainnet, there were 21,600 slots per epoch and one slot leader per slot. The Shelley era has 20 times as many slots per epoch, however only one out of five slots have a leader.

Each slot includes a single block, which is produced by the system’s slot leaders. These blocks are created in random order and there is no guarantee that all slots will be filled with a block. When there is no block included in a slot, it is called an empty slot.

Empty slots may occur when no delegate wins the leadership for that slot and therefore fails to produce a block within that time period. Empty slots also appear naturally due to network latency or simply because network participants fail to recognize winning blocks fast enough.

In the Ouroboros Praos algorithm, which builds on previous protocols by the IOHK team, each block is generated by a slot leader that randomly chooses a time slot (an interval of time) to produce a block. This way, no two leaders can be active at once and all blocks are created independently of each other.

A Little About Cardano

Cardano is a blockchain platform with a native governance token, ADA. The project was created by Charles Hoskinson, a co-founder of Ethereum, who left the company in 2014 to start Cardano.

Cardano’s team set out to create a scalable and secure cryptocurrency that could have a real-world utility. Cardano’s main innovation that gives it an edge is its use of a unique layer architecture. The Control Layer has all of the data about transfers and account balances stored on it and is similar to other blockchains (like Bitcoin). The Computation Layer runs smart contracts, handles financial calculations for loans and insurance policies, etc.

The Cardano team has big plans for the future. They want to make ADA a globally accepted method of payment and are partnering with companies around the world to accomplish this goal. They also plan to launch sidechains — separate blockchains that can interact with the main chain but are faster and more flexible.