What are Applications IDs?

As a general purpose base layer, Avail is designed to support many modular chains at the same time, providing consensus and data availability to all of them simultaneously.

How does this work? Avail headers contain an index that allows a given modular chain (or "application" in Avail terminology) to determine and download only the sections of a block that have data for that particular application.

This has very important benefits, including:

• Modular applications are largely unaffected by other uses of the base layer at the same time.
• Block sizes can increase without requiring applications to fetch more data, because they don't fetch the whole block, only what's relevant to them.

Data availability sampling is still done on the entire block, however--this is the process where clients sample very small parts of the block at random to verify availability.

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