---
title: Programs
description:
  Solana programs are executable code stored onchain. Overview of program types,
  the sBPF execution model, deployment and upgrades, and the Anchor and native
  Rust development approaches.
url: /docs/core/programs
type: conceptual
prerequisites:
  - /docs/core/accounts
related:
  - /docs/core/programs/program-execution
  - /docs/core/programs/program-deployment
  - /docs/core/programs/builtin-programs
  - /docs/core/instructions
---

A Solana program is an
[account](/docs/core/accounts/account-types#program-accounts) that contains
executable sBPF bytecode and has its `executable` flag set to `true`. Programs
are stateless. All mutable state lives in separate data accounts passed via
[instructions](/docs/core/instructions).

![Diagram of a program account, its 4 components and its loader program.](/assets/docs/core/accounts/program-account-simple.svg)

<Cards>
  <Card title="Program Execution" href="/docs/core/programs/program-execution">
    Compilation, writing programs (Anchor / Native Rust), sBPF VM, compute unit
    model, syscalls, program cache.
  </Card>
  <Card
    title="Program Deployment"
    href="/docs/core/programs/program-deployment"
  >
    Deploying, upgrading, and verifying programs. Loader-v3 instruction
    reference and loader programs.
  </Card>
  <Card title="Core Programs" href="/docs/core/programs/builtin-programs">
    System Program (with instruction reference), Vote, Stake, Config, Compute
    Budget, Address Lookup Table, and ZK ElGamal Proof.
  </Card>
  <Card title="Precompiles" href="/docs/core/programs/precompiles">
    Ed25519, Secp256k1, Secp256r1 signature verification programs. Offset
    structs and validation rules.
  </Card>
  <Card title="Syscall Reference" href="/docs/core/programs/syscall-reference">
    Complete reference for all ~30 sBPF syscalls with compute unit costs.
  </Card>
</Cards>

## Key facts

- **Compiled to sBPF**: Programs are compiled to Solana Bytecode Format (sBPF)
  via LLVM and stored in executable accounts.
- **Stateless**: All mutable state lives in separate data accounts, not in the
  program account.
- **Upgradeable**: Programs deployed with loader-v3 (BPF Loader Upgradeable) can
  be upgraded when an upgrade authority is set; revoking that authority makes
  the program immutable.

## Limits

| Limit                                          | Value                 | Source                                                                                                                                                                                                                                                          |
| ---------------------------------------------- | --------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Default heap size                              | 32 KiB                | [`HEAP_LENGTH`](https://github.com/anza-xyz/solana-sdk/blob/clock%40v2.2.3/program-entrypoint/src/lib.rs#L42)                                                                                                                                                   |
| Max heap size (adjustable)                     | 256 KiB               | [`MAX_HEAP_FRAME_BYTES`](https://github.com/anza-xyz/agave/blob/v3.1.8/program-runtime/src/execution_budget.rs#L48)                                                                                                                                             |
| Stack frame size                               | 4,096 bytes           | [`STACK_FRAME_SIZE`](https://github.com/anza-xyz/agave/blob/v3.1.8/program-runtime/src/execution_budget.rs#L37)                                                                                                                                                 |
| Max sBPF call depth                            | 64                    | [`MAX_CALL_DEPTH`](https://github.com/anza-xyz/agave/blob/v3.1.8/program-runtime/src/execution_budget.rs#L34)                                                                                                                                                   |
| Max instruction stack depth (top-level + CPIs) | 5 (9 with SIMD-0268)  | [`MAX_INSTRUCTION_STACK_DEPTH`](https://github.com/anza-xyz/agave/blob/v3.1.8/program-runtime/src/execution_budget.rs#L8), [`MAX_INSTRUCTION_STACK_DEPTH_SIMD_0268`](https://github.com/anza-xyz/agave/blob/v3.1.8/program-runtime/src/execution_budget.rs#L10) |
| Heap cost                                      | 8 CUs per 32 KiB page | [`DEFAULT_HEAP_COST`](https://github.com/anza-xyz/agave/blob/v3.1.8/program-runtime/src/execution_budget.rs#L43)                                                                                                                                                |
| Max cached programs                            | 512                   | [`MAX_LOADED_ENTRY_COUNT`](https://github.com/anza-xyz/agave/blob/v3.1.8/program-runtime/src/loaded_programs.rs#L31)                                                                                                                                            |
| Deployment visibility delay                    | 1 slot                | [`DELAY_VISIBILITY_SLOT_OFFSET`](https://github.com/anza-xyz/agave/blob/v3.1.8/program-runtime/src/loaded_programs.rs#L32)                                                                                                                                      |