diff --git a/lecture_note/docs/pintos/proj4.md b/lecture_note/docs/pintos/proj4.md
new file mode 100644
index 0000000..b5d8b15
--- /dev/null
+++ b/lecture_note/docs/pintos/proj4.md
@@ -0,0 +1,22 @@
+# Project 4: File System
+
+!!! warning "No plagiarism"
+    If you are enrolled in CS130, you may not copy code from this repository.
+
+!!! warning "急了急了急了"
+    Project 4 基于 Project 2 或 3, 希望你的 Project 足够 robust.
+
+!!! note "Overview"
+    - Task 1 : indexed and extensible files
+    - Task 2 : subdirectories
+    - Task 3 : buffer cache
+    - Task 4 : synchronization
+
+## 文件系统限制需要被你解除
+
+- 可能并发访问文件, 即 Task 4 要提供的同步
+- 文件大小不再固定
+
+## 分析
+
+这里空空的, 什么也没有.
diff --git a/lecture_note/mkdocs.yml b/lecture_note/mkdocs.yml
index cb71cb4..8a93757 100644
--- a/lecture_note/mkdocs.yml
+++ b/lecture_note/mkdocs.yml
@@ -56,4 +56,5 @@ nav:
     - Project 1: 'pintos/proj1.md'
     - Project 2: 'pintos/proj2.md'
     - Project 3: 'pintos/proj3.md'
+    - Project 4: 'pintos/proj4.md'
   # - 其他笔记:
\ No newline at end of file