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# Algorand Specifications

In addition to the Stack, the AVM has a _Scratch Space_ (or _heap_) of 256256 positions.

Like Stack values, scratch locations may hold `stackValues` (of either `uint64` or `bytes` types) and are initialized as zeroed-out `uint64` values.

> The _Scratch Space_ is an additional area of volatile memory used at runtime. It’s useful for storing values needed multiple times during program execution, or that stay the same for long periods. It provides a convenient place to keep such persistent or reusable data during the program execution.

> Important
>
> **IMPLEMENTATION:**
>
> Scratch Space [reference implementation.](https://github.com/algorand/go-algorand/blob/b7b3e5e3c9a83cbd6bd038f4f1856039d941b958/data/transactions/logic/eval.go#L650)

Scratch Space locations are mapped to 00-based integer index.

The Scratch Space is accessed by the `load(s)` and `store(s)` opcodes which move data respectively:

- From the Scratch Space to the Stack;
- From the Stack to the Scratch Space.

Application calls **MAY** inspect the _final_ Scratch Space of earlier application call transactions in the _same group_ using `gload(s')(s)`, where:

- `s` is the integer index of a Scratch Space location,
- `s'` is the integer index of an earlier application call transaction in the group.