diff --git a/src/kernel/system.rs b/src/kernel/system.rs
index bad8652..c813d96 100644
--- a/src/kernel/system.rs
+++ b/src/kernel/system.rs
@@ -30,6 +30,7 @@ impl<'a> System<'a> {
         }
     }
 
+    /// use thread_manager setter to send it system instance
     pub fn freeze(&'a mut self) {
         self.thread_manager.system.set(Option::Some(self));
     }
diff --git a/src/main.rs b/src/main.rs
index 78b9e54..2e01f7d 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,5 +1,16 @@
+
+#![warn(missing_docs)]
+#![warn(clippy::missing_docs_in_private_items)]
+
+//! Crate burritos ((BurritOS Using Rust Really Improves The Operating System)
+//! 
+//! Burritos is an educational operating system written in Rust
+//! running on RISC-V emulator.
+
+/// Contain hardware simulated part of the machine
 mod simulator;
 mod kernel;
+/// module containing useful tools which can be use in most part of the OS to ease the development of the OS
 pub mod utility;
 
 use kernel::system::System;
@@ -7,5 +18,6 @@ use simulator::machine::Machine;
 
 fn main() {
     let machine = Machine::init_machine();
-    let _system = System::new(machine);
+    let mut system = System::new(machine);
+    system.freeze();
 }
diff --git a/src/utility/list.rs b/src/utility/list.rs
index f6efb50..b3cc66f 100644
--- a/src/utility/list.rs
+++ b/src/utility/list.rs
@@ -1,9 +1,13 @@
 
+/// Data structure and definition of a genericsingle-linked LIFO list.
+/// 
+/// This is a 
 #[derive(PartialEq)]
 pub struct List<T: PartialEq> {
     head: Link<T>,
 }
 
+
 type Link<T> = Option<Box<Node<T>>>;
 
 #[derive(PartialEq)]
@@ -13,6 +17,8 @@ struct Node<T> {
 }
 
 impl<T: PartialEq> List<T> {
+
+    /// Create an empty list
     pub fn new() -> Self {
         List { head: None }
     }
@@ -94,18 +100,26 @@ impl<T: PartialEq> List<T> {
         found
     }
 
+    /// Return true if the list is empty, false otherwise
     pub fn is_empty(&self) -> bool {
         self.head.is_none()
     }
 
+    /// Turn the list into an iterator for use in a for loop per example.
+    /// 
+    /// When you iter using into_iter, elements are remove from the list
     pub fn into_iter(self) -> IntoIter<T> {
         IntoIter(self)
     }
 
+    /// Turn the list into an iterator for use in a for loop
+    /// 
+    /// When you iter using this method, elements are dereferenced
     pub fn iter(&self) -> Iter<'_, T> {
         Iter { next: self.head.as_deref() }
     }
 
+    /// Same as iter but make the iterator mutable
     pub fn iter_mut(&mut self) -> IterMut<'_, T> {
         IterMut { next: self.head.as_deref_mut() }
     }
@@ -120,6 +134,7 @@ impl<T: PartialEq> Drop for List<T> {
     }
 }
 
+/// Iterator structure for use in a for loop, pop elements before returning it
 pub struct IntoIter<T: PartialEq>(List<T>);
 
 impl<T: PartialEq> Iterator for IntoIter<T> {
@@ -130,6 +145,7 @@ impl<T: PartialEq> Iterator for IntoIter<T> {
     }
 }
 
+/// Iterator structure for use in a for loop, dereference before returning it 
 pub struct Iter<'a, T> {
     next: Option<&'a Node<T>>,
 }
@@ -144,6 +160,7 @@ impl<'a, T> Iterator for Iter<'a, T> {
     }
 }
 
+/// Same as Iter structure, returned item are mutable
 pub struct IterMut<'a, T> {
     next: Option<&'a mut Node<T>>,
 }