diff --git a/src/filesys/filehdr.rs b/src/filesys/filehdr.rs
index e69de29..e6dcad9 100644
--- a/src/filesys/filehdr.rs
+++ b/src/filesys/filehdr.rs
@@ -0,0 +1,154 @@
+use crate::simulator::disk;
+use crate::{simulator::disk::SECTOR_SIZE, utility::bitmap::BitMap};
+pub const MAX_HEADER_SECTORS: i32 = 32;
+pub const DATAS_IN_FIRST_SECTOR: i32 = (SECTOR_SIZE - 5 * 8) /8; 
+pub const DATAS_IN_SECTOR: i32 = (SECTOR_SIZE - 1 * 8) /8; 
+pub const MAX_DATA_SECTORS: i32 = ((MAX_HEADER_SECTORS-1) * DATAS_IN_SECTOR + DATAS_IN_FIRST_SECTOR);
+pub const MAX_FILE_LENGTH: i32 = ((MAX_DATA_SECTORS) * SECTOR_SIZE);
+
+use crate::DrvDisk;
+use crate::Disk;
+
+pub struct FileHdr {
+    is_dir: i32,
+    num_bytes: i32,
+    num_sectors: i32,
+    data_sectors: Vec<i32>,
+    num_header_sectors: i32,
+    header_sectors: [i32; MAX_HEADER_SECTORS as usize],
+}
+
+impl FileHdr { 
+
+    pub fn allocate(&mut self, mut free_map: BitMap, file_size: i32) -> bool {
+        self.num_bytes = file_size;
+        if file_size > MAX_FILE_LENGTH {
+            panic!("file size is too long");
+        }
+
+        self.num_sectors = (file_size + SECTOR_SIZE -1) / SECTOR_SIZE;
+        self.num_header_sectors = ((self.num_sectors - DATAS_IN_FIRST_SECTOR)+DATAS_IN_SECTOR-1) / DATAS_IN_SECTOR;
+
+        // Check if there is enough free sectors for both of them
+        if free_map.num_clear() < self.num_sectors + self.num_header_sectors {
+            return false;
+        }
+
+        for i in 0..self.num_header_sectors  {
+            self.header_sectors[i as usize]  = free_map.find();
+        }
+
+        self.data_sectors = vec![0; MAX_DATA_SECTORS as usize];
+        for i in 0..self.num_sectors  {
+            self.data_sectors[i as usize]  = free_map.find();
+        }
+
+        return true;
+    }
+
+    pub fn re_allocate(&mut self, mut free_map: BitMap, old_file_size: i32, new_file_size: i32) -> bool {
+        let mut new_num_sectors = ((new_file_size + SECTOR_SIZE -1) / SECTOR_SIZE) - self.num_sectors;
+        self.num_bytes = new_file_size;
+
+        let mut new_num_header_sectors  = (((self.num_sectors - DATAS_IN_FIRST_SECTOR)+DATAS_IN_SECTOR-1) / DATAS_IN_SECTOR) - self.num_header_sectors;
+
+        assert!(new_file_size <= MAX_FILE_LENGTH);
+
+        if free_map.num_clear() < new_num_sectors + new_num_header_sectors {
+            return false;
+        }
+        
+        for i in 0..new_num_header_sectors  {
+            self.header_sectors[(i + self.num_header_sectors)as usize]  = free_map.find();
+        }
+
+        for i in 0..new_num_sectors  {
+            self.data_sectors[(i + self.num_sectors) as usize]  = free_map.find();
+        }
+
+        return true;
+
+
+
+    }
+
+    pub fn deallocate(&mut self, mut free_map: BitMap) {
+        for i in 0..self.num_sectors {
+            assert!(free_map.test(self.data_sectors[i as usize] as usize));
+            free_map.clear(self.data_sectors[i as usize]as usize);
+        }
+
+        for i in 0..self.num_header_sectors {
+            assert!(free_map.test(self.header_sectors[i as usize] as usize));
+            free_map.clear(self.header_sectors[i as usize]as usize);
+        }
+    }
+
+    //TODO: fetchFrom WriteBack
+
+
+    pub fn byte_to_sector(&self,offset: i32) -> i32 {
+        return self.data_sectors[ (offset / SECTOR_SIZE) as usize];
+    }
+
+    pub fn file_length(&self) -> i32 {
+        return self.num_bytes;
+    }
+
+    pub fn change_file_length(&mut self, new_size: i32) {
+        self.num_bytes = new_size;
+        assert!(new_size <= MAX_FILE_LENGTH);
+
+    }
+
+    pub fn max_file_length(&self) -> i32 {
+        return self.num_sectors * SECTOR_SIZE;
+    } 
+
+    pub fn print(&self) {
+        let mut data = Vec::new();
+        println!("FileHeader contents. File size: {}. File blocks:", self.num_bytes);
+        for i in 0..self.num_sectors {
+            print!("{} ", self.data_sectors[i as usize]);
+        }
+        println!("\nFile contents:");
+        let mut k = 0;
+        for i in 0..self.num_sectors {
+            let disk = Disk::init_disk();
+            let mut drv_disk = DrvDisk::init_drv_disk(disk);
+            drv_disk.read_sector(self.data_sectors[i as usize], &mut data);
+            for j in 0..SECTOR_SIZE.min(self.num_bytes - k) {
+                let c = data[j as usize];
+                if c >= 0x20 && c <= 0x7E {
+                    print!("{}", c as char);
+                } else {
+                    print!("\\{:x}", c);
+                }
+                k += 1;
+            }
+            println!("");
+        }
+    }
+
+    pub fn is_dir(&self) -> bool{
+        return self.is_dir == 1;
+    }
+
+    pub fn set_file(&mut self) {
+        self.is_dir = 0;
+    }
+
+    pub fn set_dir(&mut self) {
+        self.is_dir = 1;
+    }
+
+}
+
+#[cfg(test)]
+mod test {
+
+    #[test]
+    fn test_allocate() {
+
+    }
+}
\ No newline at end of file
diff --git a/src/filesys/mod.rs b/src/filesys/mod.rs
new file mode 100644
index 0000000..14f5368
--- /dev/null
+++ b/src/filesys/mod.rs
@@ -0,0 +1,6 @@
+pub mod directory;
+pub mod filehdr;
+pub mod filesys;
+pub mod fsmisc;
+pub mod oftable;
+pub mod openfile;
\ No newline at end of file