diff --git a/src/fs.cpp b/src/fs.cpp
new file mode 100644
index 0000000..8911d28
--- /dev/null
+++ b/src/fs.cpp
@@ -0,0 +1,75 @@
+#include "fs.hpp"
+#include <cstdint>
+
+namespace vc5::filesys {
+
+constexpr auto Ok = Status::Ok;
+
+using BlockData = std::array<uint8_t, block_size>;
+
+void Fs::init()
+{
+    m_super = SuperBlockData {
+        .block_bitmap = {},
+        .inode_bitmap = {},
+        .inode_blocks = {},
+    };
+    write_superblock();
+}
+
+Status Fs::make_directory()
+{
+    uint16_t id;
+    if (auto result = next_inode_id(id); result != Ok) {
+        return result;
+    }
+
+    auto node = INodeData {
+        .id = id,
+        .flags = static_cast<uint16_t>(INodeType::Directory),
+        .blocks_count = 0,
+        .blocks = {},
+    };
+}
+
+Status Fs::write_new_inode(INodeData& data)
+{
+    uint16_t block_id = data.id / inodes_per_block;
+    uint16_t offset = data.id % inodes_per_block * inode_size;
+
+    BlockData block;
+    m_disk->read(&block[0], block_id);
+}
+
+Status Fs::next_inode_id(uint16_t& id)
+{
+    for (uint16_t map_idx = 0; map_idx < sb_inode_bitmap_count; ++map_idx) {
+        auto& map = m_super.inode_bitmap[map_idx];
+
+        for (uint16_t bit_idx = 0; bit_idx < 16; ++bit_idx) {
+
+            if ((map >> bit_idx & 1) == 0) {
+                id = map_idx * sb_inode_bitmap_count + bit_idx;
+                return Ok;
+            }
+        }
+    }
+    return Status::INodeAllocFail;
+}
+
+Status Fs::read_superblock()
+{
+    BlockData block;
+    m_disk->read(&block[0], super_block_location);
+    m_super = *reinterpret_cast<SuperBlockData*>(&block[0]);
+    return Ok;
+}
+
+Status Fs::write_superblock()
+{
+    m_disk->write(
+        reinterpret_cast<const uint8_t*>(&m_super), super_block_location);
+    return Ok;
+}
+
+}
diff --git a/src/fs.hpp b/src/fs.hpp
new file mode 100644
index 0000000..58d1df7
--- /dev/null
+++ b/src/fs.hpp
@@ -0,0 +1,73 @@
+#pragma once
+
+#include "block_device.hpp"
+#include <cstddef>
+#include <cstdint>
+
+namespace vc5::filesys {
+
+enum class Status : uint16_t {
+    Ok,
+    INodeAllocFail,
+};
+
+constexpr uint16_t block_size = 0x200;
+constexpr uint16_t name_max_len = 255;
+
+struct DirEntryData {
+    uint16_t inode;
+    uint16_t name_len;
+    std::array<uint8_t, name_max_len> name;
+};
+
+enum class INodeType : uint16_t {
+    File = 0,
+    Directory = 1,
+    Symlink = 2,
+};
+
+constexpr uint16_t inode_size = 32;
+constexpr uint16_t inodes_per_block = block_size / inode_size;
+constexpr uint16_t inode_blocks_count = 8;
+
+struct INodeData {
+    uint16_t id;
+    uint16_t flags;
+    uint16_t blocks_count;
+    std::array<uint16_t, inode_blocks_count> blocks;
+};
+
+constexpr uint16_t super_block_location = 0x400;
+constexpr uint16_t sb_block_bitmap_count = 8;
+constexpr uint16_t sb_inode_bitmap_count = 8;
+constexpr uint16_t sb_inode_blocks_count = 16;
+
+struct SuperBlockData {
+    std::array<uint16_t, sb_block_bitmap_count> block_bitmap;
+    std::array<uint16_t, sb_inode_bitmap_count> inode_bitmap;
+    std::array<uint16_t, sb_inode_blocks_count> inode_blocks;
+};
+
+class Fs {
+public:
+    explicit Fs(BlockDevice& disk)
+        : m_disk(&disk)
+    {
+    }
+
+    void init();
+
+private:
+    Status make_directory();
+
+    Status write_new_inode(INodeData& data);
+    Status next_inode_id(uint16_t& id);
+
+    Status read_superblock();
+    Status write_superblock();
+
+    BlockDevice* m_disk;
+    SuperBlockData m_super;
+};
+
+}
diff --git a/src/io_device.cpp b/src/io_device.cpp
index fa149ea..e9d7bc8 100644
--- a/src/io_device.cpp
+++ b/src/io_device.cpp
@@ -26,7 +26,7 @@ constexpr uint64_t char_data(uint8_t ch)
         case '$': return 0x00187e6218467e18;
         case '%': return 0x0022562c18346a44;
         case '&': return 0x00784c38724a4638;
-        case '\'': return 0x0018180000000000;
+        case '\'': return 0x0018181800000000;
         case '(': return 0x000c18303030180c;
         case ')': return 0x0030180c0c0c1830;
         case '*': return 0x0000241818240000;
@@ -91,7 +91,7 @@ constexpr uint64_t char_data(uint8_t ch)
         case 'a': return 0x0000003c023e423e;
         case 'b': return 0x004040407c42427c;
         case 'c': return 0x000000003c40403c;
-        case 'd': return 0x00020202023e423e;
+        case 'd': return 0x000202023e42423e;
         case 'e': return 0x0000003c427c403c;
         case 'f': return 0x00000c103c101010;
         case 'g': return 0x003e645840784438;
diff --git a/src/vm.cpp b/src/vm.cpp
index cbf7d90..755087d 100644
--- a/src/vm.cpp
+++ b/src/vm.cpp
@@ -195,6 +195,11 @@ struct InsReader {
     VM* vm;
     uint16_t ins;
 
+    auto op() -> Op
+    {
+        return static_cast<Op>(ins & 0b11'1111);
+    }
+
     auto to_u16() const -> uint16_t
     {
         return ins;
@@ -277,7 +282,8 @@ int VM::run_instruction()
         return -1;
 
     auto ins = InsReader(*this);
-    auto op = static_cast<Op>(ins.to_u16() & 0b11'1111);
+    auto op = ins.op();
+
     std::println(
         "    [{: >3x}]: 0x{:04x} {: <6} {:04b} {:04b} {:04b} {:04b}    {:04x}",
         ip,