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Formatting, Files Systems and Partitioning

How do you prepare your hard disk for installation of an operating system?  Can you use a hard disk to store files on only?  Can you install more than one operating system on a hard disk?   Read on and find out.

Introduction

Formatting

Physical Formatting

Logical Formatting

File Systems

FAT Based File Systems

FAT 16

FAT 32

NTFS

Ext File Systems

Ext2

Ext3

Netware File System

Partitioning

Booting Up

Introduction

Assuming you wish to install one or more operating systems onto a hard disk, then you need to know about...

• operating system requirements:- minimum memory, CPU speed, minimum disk space.

• logical formatting

• file systems 

• partitioning.

Knowledge of the above ensures that a disk is correctly organised for the operating system you wish to install.  It also gives you the power to structure one or more disks so that installation of more than one operating system is possible.

Formatting

 Physical Formatting

A magnetic disk is physically formatted (also call a low-level format) into a tracks, sectors and cylinders, usually by the manufacturer.  Physical formatting divides the disk into basic elements so that data can be read from the disk.

After formatting, the magnetic quality of the surface may gradually deteriorates. the read-write heads may find it difficult to read the magnetic properties of sectors.  Any sector that becomes impossible to read is marked as a bad sector and is ignored by the computer.

Logical  Formatting

After physical formatting, the disk must be logically formatted.  This process places a file system on disk and allows an operating system to store and retrieve files.  Different operating systems (Windows 9x, NT, Linux etc.) use different file systems.  So a disk must be formatted using the correct file system for the operating system that you  plan too install.

Do you know the type of file system commonly used by the operating systems listed below?

Operating System	File System
DOS
Windows 95
Windows 98
Windows NT
Windows 2000
Windows XP
Linux
Novell Netware

After a disk is formatted using a particular file system, you are usually limited to installing one operating system.  However, it is possible to logically format a disk using more than one file system using a technique called partitioning.  

Partitioning effectively divides up you hard disk into different parts, allowing you to logically format each part separately, using different file systems and installing different operating systems, if you choose.

File Systems

A files system is the method used to organise data on a disk.  It controls the allocation of disk space to files, and associates each file with a filename, directory, permissions, and other information. 

A file system is a structure used for storing and managing data.  It includes a boot, file and directory structures.  A file system also needs to..

• track free and used space

• maintain file and directory names

• record where each file is located on disk

The choice of file system is an important one since it affects performance, recovery from errors, compatibility with other operating systems, limitations on partition and file sizes, and so on.  Common file systems are:-

File System	OS	Accessible by
FAT 16	DOS, Win3.1, Win95	Win98/NT/2000/ ME/XP/Linux
FAT 32	Win95 (2nd release), Win98, ME, 2000,	Win98/NT/2000/ ME/XP/Linux not DOS, Win3.1, Win95(1st release)
NTFS	WinNT, 2000, XP	WinNT, 2000, XP not DOS, Win3.1, Win95, Win98, read-only for Linux
EXT2 or EXT3	Linux	Linux or Unix not DOS or Windows
Netware	Novell Netware	Netware not DOS, Windows, Linux or Unix

FAT Based File Systems

FAT  is characterized by the use of a File Allocation Table and clusters.  A cluster is a small fixed number of sectors and are the smallest unit of data storage.  FAT records which clusters are allocated, which are free and where files are stored within clusters.  

The FAT table also has a root directory that records information about each sub-directory. Each sub-directory entry contains information about files in the form of file name, creation date, the first cluster used by the the file and file attributes, (hidden, read-only, etc.) 

FAT 16 

FAT16 was the standard partition type up to Windows 95 - used by DOS, Windows 3.1 and Windows 95 (1st release).  Although FAT16 partitions are supported by all versions of Windows, FAT16 partitions are limited to a maximum of 2Gb. 

FAT 32

FAT32 is supported by Windows95 second edition onwards, including Windows 2000 but not WinNT.   FAT32 partitions are the standard with Windows 98. 

FAT32 is based on 32-bit file allocation table entries rather than 16-bit entries used by FAT16.  As a result, FAT32 supports larger disks or partition sizes than FAT16.  Although the theoretical maximum size for FAT32 is 2 TB, Windows98's scandisk only supports 128Gb, and Windows 2000 does not permit the creation of FAT32 disks larger than 32Gb. 

Unlike file systems such as NTFS ( WinNT, 2000, XP) and EXT (Linux), FAT file systems are unable to hold information on file ownership and permissions.  Since Linux supports both reading from, and writing to FAT16 and FAT32 partitions, quite often FAT partitions are used to allow file sharing between Linux and Windows on a dual-boot system. 

NTFS

NTFS (new technology file system) is a file system introduced with Windows NT v4.0.   Windows 2000 and XP also use NTFS.  Linux, installed on another partition or disk, can only access an NTFS partition in read-only mode.  NTFS partitions are not accessible from Windows 95 or 98. 

Like FAT 16 and FAT32, NTFS uses clusters, but a cluster size of 512 bytes can be specified which reduced file fragmentation and wasted disk space.  So NTFS performs well on large disks.  Unlike FAT systems, NTFS supports the holding of information on file ownership and permissions.

Ext File System

Linux supports a wide variety of file systems. Extfs is an old file system used in early Linux systems. Newer versions of this system are Ext2 and Ext3.

Ext2

The Ext2 file system is the default file system for Linux, although Ext3 is often used now.   It supports partitions of up to 4 Terabytes in size, while a single file can be up to 2 Gigabytes.   Filenames can be up to 255 characters long.  Ext2 is able to manage really big partitions. 

Ext3

Ext3 uses a new journaling file system which offer a number of advantages over the traditional ext2.  Whenever a computer is switched off without a proper shutdown there is the possibility that data on the disk will become corrupted - that is, some of the data will have been written half-written to disk.  If a system crashes it usually goes through a routine to check the disk for errors - fsck in Linux and scandisk or chkdsk in Windows.  This is time-consuming, especially on today's very large disks. 

A journaling file systems get rid of these problems.  Instead of writing modified files directly onto their area on the disk, the system maintains a journal on the disk which describes all the changes which must be made to disk. Then, a background process takes each journal entry, makes the change and marks it as completed. If the system is halted without a shutdown, any pending changes are performed when it is restarted and the system is ready to continue running in seconds. Incomplete entries in the journal are discarded. This guarantees consistency and removes the need for a long and complex file system check on bootup.

Linux Swap

The Linux swap partition is an amount of disk space in which Linux temporarily writes data from RAM to free up memory for other processes. 

Netware File System

The Novell Netware operating system uses the Netware File System.  It was developed specifically for Netware servers.  Most other operating systems cannot read a partition with this system installed.

Partitioning

After a disk has been physically formatted and normally before it is logically formatted, a disk can be sectioned up into discrete units called partitions.  Effectively, each partition is separate from another partition and can be logically formatted with a file system different from file systems on other partitions.

This is tremendously useful for:-

• installing more than one operating system onto a disk.  You can just give each OS it's own partition.  

• Separating data

Once a partition is logically formatted it is called a volume and you can give this volume a name if you like, to help identify it.

The picture below shows a disk partitioned into two volumes.  The first volume has an NTFS file system and the volume label is WinXP.  The second volume has a FAT32 file system and the volume label is MYFILES.

Now, there are three types of partitions, primary, extended and logical.  

Primary Partitions

A primary partition can contain an operating system and/or data files.  There is a limit to the number of primary partitions a disk can have.  A disk can be sectioned up into at most four primary partitions.

One of the partitions must be set as the active partition.  The active partition is the one used at boot up time and so it should contain an operating system.  You can change the active partition at any time to another primary partition using a utility such as DOS's fdisk.

Only one primary partition can be active at any one time.

Extended Partitions

Extended partitions are used to overcome the four-partition limit on primary partitions.  Effectively, an extended partition is a container for logical partitions and it can contain an unlimited number of them.  This is useful for further partitioning of the disk.

For example, say you wish to have five partitions.  You could create three primary partitions with one of the primary partitions containing an extended partition containing two logical partitions.

Extended partitions in themselves do not hold data, they just hold logical partitions.   

Logical Partitions

Logical partitions can contain an operating system and/or data files, just like primary partitions.  However, you should be aware that not all operating systems can boot from a logical partition.

The picture below shows a disk that has been partitioned into three primary partitions, one of which is really an extended partition.  Inside this extended partition there are four logical partitions. 

~Now try the activity~

Booting Up

How does a computer manage the booting up process?  If you have more than one partition or more than one disk, how does it know which OS to load?

On booting up, the BIOS ROM runs it's startup procedures.  The last procedure is the boot routine.  This routine reads the Master Boot Record (MBR) on the first sector of the active partition.  The MBR consists of a partition table and information on which is the currently active partition.  The active partition's operating system boot routines are then located and loaded.

If there is more than one primary partition on the disk, then the first sector of each bootable partition (containing an OS) contains the boot record for the OS.  Each OS when it is first installed usually writes it's boot record to the first sector of its partition.

Some Questions

Examine the picture below:-

~Now try the activity~

Examine the picture below:-

~Now try the activity~