diff --git a/CMakeLists.txt b/CMakeLists.txt
index fe3f4b1..dd73d4d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -40,9 +40,12 @@ target_sources(nf7
     nf7.cc
     nf7.hh
 
+    common/dir.hh
     common/queue.hh
     common/type_info.hh
     common/yas.hh
+
+    file/system_dir.cc
 )
 target_link_libraries(nf7
   PRIVATE
diff --git a/common/dir.hh b/common/dir.hh
new file mode 100644
index 0000000..f41ca67
--- /dev/null
+++ b/common/dir.hh
@@ -0,0 +1,48 @@
+#pragma once
+
+#include <map>
+#include <memory>
+#include <string>
+#include <string_view>
+
+#include "nf7.hh"
+
+
+namespace nf7 {
+
+class Dir : public File::Interface {
+ public:
+  class DuplicateException;
+
+  Dir() = default;
+  virtual ~Dir() = default;
+  Dir(const Dir&) = default;
+  Dir(Dir&&) = default;
+  Dir& operator=(const Dir&) = default;
+  Dir& operator=(Dir&&) = default;
+
+  virtual File& Add(std::string_view, std::unique_ptr<File>&&) = 0;
+  virtual std::unique_ptr<File> Remove(std::string_view) noexcept = 0;
+
+  virtual std::map<std::string, File*> FetchItems() const noexcept = 0;
+};
+class Dir::DuplicateException : public Exception {
+ public:
+  using Exception::Exception;
+};
+
+class DirItem : public File::Interface {
+ public:
+  DirItem() = default;
+  virtual ~DirItem() = default;
+  DirItem(const DirItem&) = delete;
+  DirItem(DirItem&&) = delete;
+  DirItem& operator=(const DirItem&) = delete;
+  DirItem& operator=(DirItem&&) = delete;
+
+  virtual void UpdateTree() noexcept { }
+  virtual void UpdateMenu() noexcept { }
+  virtual void UpdateTooltip() noexcept { }
+};
+
+}  // namespace nf7
diff --git a/file/system_dir.cc b/file/system_dir.cc
new file mode 100644
index 0000000..8301718
--- /dev/null
+++ b/file/system_dir.cc
@@ -0,0 +1,95 @@
+#include <map>
+#include <memory>
+#include <string>
+#include <string_view>
+
+#include <yas/serialize.hpp>
+#include <yas/types/std/map.hpp>
+#include <yas/types/std/string.hpp>
+
+#include "nf7.hh"
+
+#include "common/dir.hh"
+#include "common/ptr_selector.hh"
+#include "common/type_info.hh"
+#include "common/yas.hh"
+
+
+namespace nf7 {
+namespace {
+
+class Dir final : public File, public nf7::Dir {
+ public:
+  static inline const GenericTypeInfo<Dir> kType = {"System", "Dir", {"DirItem"}};
+
+  using ItemMap = std::map<std::string, std::unique_ptr<File>>;
+
+  Dir(Env& env, ItemMap&& items = {}, bool shown = false) noexcept :
+      File(kType, env), items_(std::move(items)), shown_(shown) {
+  }
+
+  Dir(Env& env, Deserializer& ar) : Dir(env) {
+    ar(items_, shown_);
+  }
+  void Serialize(Serializer& ar) const noexcept override {
+    ar(items_, shown_);
+  }
+  std::unique_ptr<File> Clone(Env& env) const noexcept override {
+    ItemMap items;
+    for (const auto& item : items_) {
+      items[item.first] = item.second->Clone(env);
+    }
+    return std::make_unique<Dir>(env, std::move(items));
+  }
+
+  void MoveUnder(File::Id parent) noexcept override {
+    File::MoveUnder(parent);
+    for (const auto& item : items_) {
+      item.second->MoveUnder(id());
+    }
+  }
+
+  File& Add(std::string_view name, std::unique_ptr<File>&& f) override {
+    const auto sname = std::string(name);
+
+    auto [itr, ok] = items_.emplace(sname, std::move(f));
+    if (!ok) throw DuplicateException("item name duplication: "+sname);
+
+    auto& ret = *itr->second;
+    if (id()) ret.MoveUnder(id());
+    return ret;
+  }
+  std::unique_ptr<File> Remove(std::string_view name) noexcept override {
+    auto itr = items_.find(std::string(name));
+    if (itr == items_.end()) return nullptr;
+
+    auto ret = std::move(itr->second);
+    items_.erase(itr);
+    if (id()) ret->MoveUnder(0);
+    return ret;
+  }
+  std::map<std::string, File*> FetchItems() const noexcept override {
+    std::map<std::string, File*> ret;
+    for (const auto& item : items_) {
+      ret[item.first] = item.second.get();
+    }
+    return ret;
+  }
+
+  void Update() noexcept override;
+
+  File::Interface* iface(const std::type_info& t) noexcept override {
+    return PtrSelector<nf7::Dir>(t).Select(this);
+  }
+
+ private:
+  ItemMap items_;
+
+  bool shown_;
+};
+
+void Dir::Update() noexcept {
+}
+
+}
+}  // namespace nf7