1. File Structure 2018, Spring Pusan National University Joon-Seok Kim
File Systems
File Structure
2018, Spring
Pusan National University
Joon-Seok Kim

2. File
A collection of
information
information

3. System Where is the file that I am looking for?
A way of organizing something which follows a set of rules

4. Aisles #1 #2 #3 #4
Blocks #5 #6
File System
New File

5. File From user’s point of view From user process’s point of view
A named, persistent collection of data
From user process’s point of view
A sequence of bytes of arbitrary length
From operating system’s point of view
A collection of disk blocks

6. Logical File Structure
Flat file of bytes
Fixed-length records
Variable-length records

8. File System Levels User processes File system implementation
File system interface
(system calls)
File system implementation
Device driver interface
I/O system implementation
Hardware interface
Disk hardware

9. What is a File System? File system Partition
A way of organizing and storing files on any storage device such as a hard disk drive, solid-state drive
A collection of files, blocks, directories, and file descriptors, all on one logical disk
Partition
Each storage device has one or more partitions, and each partition is formatted with a file system.
The formatting process simply creates an empty file system of that type on the device.

10. Types of File Systems Disk file systems Distributed file systems
Special file systems

11. Examples of Disk File System
Operating system
Default file systems
Unix
Unix File System (UFS1, UFS2)
MINIX
MINIX File System
Linux
Extended File System (ext2, ext3, ext4)
Extents File System (XFS)
Mac OS
Hierarchical File System (HFS, HFS+)
MS-DOS
File Allocation Table (FAT12, FAT16, FAT32)
Windows
New Technology File System (NTFS)

12. File system descriptor
Layout of a File System
block number 1 2 3 …
Boot block
File system descriptor
File descriptors 0-7
File descriptors 8-15
File descriptors 16-23
...
reserved
block
Data blocks

13. File System Descriptor
Called superblock in UNIX
Contents of the file system descriptor
The total size of file system
The size of the file descriptor area
The first block on the free block list
The location of the file descriptor of the root directory
The time the file system was created, last modified, and last used
Other file system meta-data

14. File Descriptors Called inode (index node) in UNIX
Data structure that records all the meta-information about the file
Maintained by the file system
Separate from file itself
Usually attached or connected to the file
Some information visible to user/application
Dates, permissions, type, name, etc.
Some information primarily for OS
Location on disk, locks, cached attributes