Partitioning hard disks

Partitioning a hard disk is a task that is often taken for granted by advanced users, yet is viewed as a black art by those just developing their expertise.

This feature aims to demystify the process, explaining how and why to do it. Although this guide is primarily aimed at less experienced users, it’s also a handy refresher for more advanced readers ­ not everyone partitions disks on a daily basis, and it’s often easy to forget the basics.

We recommend that if you’re planning to change the partitions on a non-empty drive, you first let Windows check your disks for errors (right-click on the drive in Windows Explorer, click Properties, then the Tools tab, then the ‘Check now’ button).

When you’ve done this make sure you’ve backed up all your data onto a separate physical hard drive or CD/DVD. It’s also a good time to dig out your system installation disc and licence key.

Why use partitions?
Historically, one of the main reasons for splitting a hard disk was to run multiple operating systems: perhaps different versions of Windows or a combination of Windows and Linux. When multiple operating systems are installed on separate partitions, a program called a boot loader will ask which one should be launched when the PC starts.

Over time, hard disks have grown so big that partitioning is now often used solely to make the available space more manageable. Backing up and managing this much data is an unwieldy process, so splitting a physical hard disk into several smaller, logical drives (partitions) is an attractive option.

This is never truer than when backups are made using one of the increasingly popular disk-imaging programs. These work by making an image of an entire partition instead of copying individual files, and they can use either a second partition or a different physical disk to store the duplicate image.

Another good use for a partition is to organise data. By keeping data separate from the partition containing Windows and its installed software, file management and backing up are simplified, while sharing a partition on a network makes it easy to draw the line between what you want to keep private and what you allow others to see.

Every partition on a disk can be separately formatted with a different filesystem, and it’s the filesystem that determines where and how data is stored. Windows XP and Windows Vista work best when formatted as NTFS, but Windows ME and Windows 98 were designed for Fat 32, and Windows 95 for Fat 16.

Splitting a disk and formatting one of the partitions as Fat 16, for example, ensures that when shared over a network or by multiple operating systems installed on the same PC, at least one partition will be readable by all of them.

Partitioning a new hard disk
When installing Windows XP on a new hard disk, its partitioning and formatting are handled by the Windows installation program. But if you’ve added a hard disk to an existing Windows XP PC, you’ll need to partition and format the new disk yourself.

Regardless of whether the new disk is fitted internally or attached to a USB port, the techniques are the same and are handled through the Microsoft Management Console (MMC). To use this, open Control Panel and click Administrative Tools. In the Administrative Tools window, double-click Computer Management. In the Computer Management console, double-click Disk Management. Alternatively, simply type ‘diskmgmt.msc’ in the Run box on the Start menu.

Within the Disk Management console, each physical hard disk is identified by number, starting with Disk 0. The exisiting partitions on each hard disk are displayed alongside. Formatted partitions are labelled with their name, size, filesystem and the Windows drive letter, while unpartitioned and unformatted disks are listed simply as Unallocated.