INTRODUCTION TO FILE

SYSTEMSBenedicta Mekoma and Jennifer

Ruth Balkeen

OUTLINE

Introduction to File Systems and their function

FAT (File Allocation Table)

NTFS (New Technology File System)

FUNCTION OF A FILE SYSTEM

File -is defined as a group of data which is created to be identified for future use.

File properties – each file has attributes (certain characteristics), dates, times, specific structures and user permissions.

Function of a file system – It’s a system to organise files. This is essential to ensure the files are used correctly by the OS (Operating System).

FUNCTION OF A FILE SYSTEM CONTINUED

Management of a File System – This is essential and helpful for larger files as their data will be stored in many fields known as sectors. This allows the information stored in such a file to be retrieved and read in the correct order.

Different File Systems – FAT (File Allocation Table) is an older file

system that has been used for many years.

NTFS (New Technology File System) is a more recent file system.

THE FAT FILE SYSTEM It is a simple and common file system. Deemed simple as there are only a few

data structures making it less complex. Data structures – (1) Cluster – basic storage unit for a file(2) Directory – tells you the file name,

length of the file and where it begins i.e. file cluster/starting cluster

(3) FAT – tells you current status of the file cluster and points to the next cluster

DIFFERENT FAT FILE SYSTEMS

FAT 12 FAT 16 FAT 32

Purpose Floppies and small hard drives

Small to large hard drives

Large to very large hard drives

Size of each FAT entry

12 bits 16 bits 28 bits

Maximum number of clusters

4,096 65,536 268,435,456

Supported cluster sizes

512B – 4KB 2KB – 32KB 4KB – 32KB

Maximum volume size

16MB 2GB 2TB

HOW THE FILES ARE STORED AND ORGANISED Directory Entry – Each file is referenced and

described in a separate directory entry. This directory entry is stored within a partition.

A partition is defined as a collection of consecutive sectors in a volume. This contains the file name, size in bytes, starting file cluster and other metadata (creation date, last accessed and time stamps).

Data Content – is not stored in Directory Entry but in clusters (data allocation units). Clusters have one or more sectors where a file is stored. If a file is too large for one cluster it is assigned more clusters. These are then stored sequentially so a file can retrieved with it being in the correct order to be read and understood by the user.

512bytes per sector.

STRUCTURE OF THE FAT FILE SYSTEM

(1) RESERVED

AREA

(2) FAT AREA

(3) DATA AREA

(1)Reserved Area – begins in sector 0 and the next sector 1 contains the Volume Boot Sector. The VBR sector indicates the number and size of FATs, number of sectors per cluster and size of Reserved Area.

(2)Fat Area – begins directly after Reserved Area and there can be one or two FATs. This area tracks the sequence of the clusters and also tracks and identifies clusters unallocated that are available for storage.

(3)Data Area – begins directly after FAT Area. Root Directory located at beginning of this area where Directory Entry is stored with filename and metadata.

THE NEW TECHNOLOGY FILE SYSTEM

This filing system is more complex and offers

multiple enhancement that increases security

and overall performance.

Uses advanced data structures to improve

reliability and disk utilization

Supports file level encryption

Supports file compression

Offers security access control

Improved support for metadata

What is metadata?

NTFS CONTINUED Metadata Files: used by NTFS to manage the filing system. .

All metadata files begin with a $ dollar sign.

Supports file/folder ownership

Supports alternate data streams: A file can be opened

using Microsoft word or Microsoft word pad.

Cluster mapping: identifies bad clusters and moves file to

another cluster. Can be used to hide data, always examine.

Supporting operating systems : Windows NT, Windows

2000, Windows XP, Vista, Windows 7

Everything is a file and every file entry can be located in the

$MFT table – Master file table

$MFT – MASTER FILE TABLE

This is a database which contains details of every file in the volume.

Informs the OS of a file’s location and what directory can be found.

Holds record of the metadata files.

The $MFT record contains information such as:

File Name

Last Access

Last Modified

File created

MFT Record number

If the $MFT table is lost, so would all the structures needed to restore a

file

Also is the $MFTMirr- This stores a duplicate copy of whatever the $MFT

holds and assists in system recovery.

IDENTIFYING ACTIVE FILE SYSTEM - NTFS

IDENTIFYING ACTIVE FILE SYSTEM – FAT32

PERMISSIONS

SUMMARY NTFS is chosen for its ability for

recoverability. Fault tolerance, data redundancy and file security.

A selected choice by businesses and corporations because it supports mission critical applications.

BENNY AND JENNY QUIZ TIME

What is your understanding of a file system? What does FAT stand for? And NTFS? And $MTF? Mention the three data structures of a FAT

file system? Describe the importance of an $MFT

table?

SO THAT’S ALL ON THE INTRODUCTION TO FILE SYSTEMS

ANY QUESTIONS?

Image courtesy of Angela Mayfield 2010