# PPerl Architecture

How pperl is built, what sets it apart from upstream Perl 5, and the
subsystems a working programmer reaches for when they want more than
"run this Perl script" — the JIT, the FFI, the native-module layer,
and the dual runtime.

This guide is descriptive, not a tutorial. Read it to understand
*how* pperl does what it does and *why* certain things behave the
way they do. Per-function behaviour lives in the
[reference tree](../../p5/index).

```{toctree}
:maxdepth: 1

runtimes
jit
ffi
native-modules
differences-from-upstream
```