Disk Preparation
Hard Disk Partitioning Theory
What's a partition and how many should I have...?
Disk Preparation

I recommend you read The Right Order section before continuing

The Black Art of Partitioning is a way of dividing< the hard disk into usable blocks, perhaps making a single physical hard drive look like many. Click here for a mini Windows Explorer view of a single physical hard disk with multiple partitions. Multiple partitions can appear as logical drives in Windows Explorer, such as C:, D:, E:, etc. all referring to one single physical hard disk, but appearing as many. Partitioning must be undertaken before a disk can be formatted.

Why bother?

Most of us are used to one partition - the C: drive - which takes up the whole of the physical hard disk. The system then allocates the D: letter to the CD-ROM drive and so on. So why partition a disk? Well there are many reasons. In the linked example above, multiple logical drives are used to organise the single hard disk into functional areas, each with its own label.

The C: drive is used for Windows, program and system files, the D: drive is used for games, the E: drive is used to store graphics and the F: drive is used for archived files. Although there is only one hard disk, the system treats these logical drives as if each were a separate hard drive in its own right.

If you want to boot your machine to multiple operating systems (say Win98 and WinNT) it's best to use more than one partition. Partitions can be useful for backups; making the partition size the same size as a backup media (ie a compact disc) means that data copied to that 650MB sized logical drive will fit nicely onto a burned CD. Partitions can be hidden and unhidden, which can be a useful way of keeping backups, storing disk (ie Norton Ghost) images, adding some security and so on.

Partitions and Logical Drives

A disk can have a maximum of four Primary Partitions, of which only one can be 'Active' at any one time. An operating system must be on a primary partition and will usually only be bootable if that partition is made the active one (some multi-boot menus can get around this). Microsoft operating systems can't cope with multiple primary partitions, so only one can be 'visible' and the rest must be 'hidden'.

For a Microsoft OS to be able to use multiple drives as in the above linked example, the disk must be partitioned with Logical Drives. Logical drives have to sit within an Extended Partition, which must be created first. If an extended partition is used on a hard disk, then only three primary partitions can be used, instead of four. There is no practical limit to the number of logical drives which can be put in an extended partition, although each needs a drive letter to reference it. Operating systems cannot boot from logical drives and must be installed on a primary partition.

Scenario One

In this first example, the whole of the physical hard disk contains one primary partition. When formatted the operating system will see this as the C: drive. DOS can only 'see' a partition of up to 2.1GB. Windows (from 95 onwards) can recognise much larger partitions...

Single primary partition

Scenario Two

Two primary partitions have been made, usually to boot to two separate operating systems such as Windows 98 and Windows NT. Booting to either partition/OS will show that partition as the C: drive and will not recognise the other as a usable partition. Only one partition can be active and only one can be 'visible' - the other partition is 'hidden'. Remember drive letters (C:, D:, E:, etc) are allocated by the operating system and not the partitioning software, so they are dynamic and may change depending on the OS which has been booted..

Two primary partitions

Scenario Three

A primary partition and an extended partition have been created. The logical drives sit in the extended partition. A bootable operating system can only reside on a primary partition - you cannot boot to a logical drive. This system would see primary partition A as the C: drive, logical drive 1 as the D: drive and logical drive 2 as the E:drive..

Maximum number of primary partitions on a hard disk is four..

Max four primary partitions

Using an extended partition reduces the maximum number of primary partitions to three..

Max three primary partitions with extended partition

Formatting the disk
The process of partitioning has to take place first. After the partition(s) have been defined, each primary partition and logical drive then needs to be formatted. Refer to the Disk Formatting and Boot Disks sections.
- A.

Put 24.02.2002 | | Refresh Page |