> For the complete documentation index, see [llms.txt](https://subsembly.gitbook.io/subsembly/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://subsembly.gitbook.io/subsembly/getting-started/substrate-essentials.md).

# Substrate Essentials

Substrate knowledge base

### Substrate

**Substrate** takes a modular approach to blockchain development and defines a rich set of primitives that allows developers to make use of powerful, familiar programming idioms.

For more information about Substrate, please refer to their in-depth [documentation](https://substrate.dev/).

### Runtime

> The runtime of a blockchain is the business logic that defines its behavior. In Substrate-based chains, the runtime is referred to as the "[state transition function](https://substrate.dev/docs/en/knowledgebase/getting-started/glossary#state-transition-function-stf)"; it is where Substrate developers define the storage items that are used to represent the blockchain's [state](https://substrate.dev/docs/en/knowledgebase/getting-started/glossary#state) as well as the [functions](https://substrate.dev/docs/en/knowledgebase/learn-substrate/extrinsics) that allow blockchain users to make changes to this state.

### How is it related?

Substrate can be used in three ways:

* **With the Substrate Node -** run node with runtime just by providing chain specification file to node
* **With Substrate FRAME -** run node with your custom runtime
* **With Substrate Core -** design and implement runtime from scratch and compile targeting **`WebAssembly`**. This is what **`Subsembly`** utilises.

Since **`Substrate`** supports **`WebAssembly`** runtimes, anything that compiles down to that is theoretically able to serve as a Substrate runtime. AssemblyScript is a language very similar to TypeScript that compiles down to WebAssembly and **`Subsembly`** is an AssemblyScript framework.