Hard Drives and Partitions

    The main storage device on a PC is a hard drive.  There may be one or more, though it is rare to have more than two.  That is the physical arrangement.. "But my Windows system shows 4 HDs" someone says.  Each hard drive may be divided up into sections called partitions.  Windows treats the partitions as separate HDs labelling them C, D, E, F for instance, as if they were physically separate units.

    There is no basic limit to the number of sections or partitions that may be created on a drive but for historical reasons the way these are arranged is far from straightforward.  Partitions are not all created equal - you can't just create say 10 partitions of 10GB on a 100GB drive, unfortunately.  (Daft isn't it!).  There are three different types of partition.
There can be up to 4 primary partitions on a hard drive and no more.  If more than four partitions are required an Extended Partition must be created.  Then within that a number of Logical Partitions may be created.  Note that an Extended Partition is only a container for Logical Partitions.  That is how a drive may be divided into a large number of sections (partitions) and Windows have umpteen HDs apparently.

Windows needs to be installed into a Primary partition but Linux (and hence Ubuntu) is not fussy and works perfectly well when installed into either a Primary or Logical Partition.  Partitions may be hidden in Windows and only visible using a 3rd party partition editor (or viewer).  

Many PCs sold by the major outlets often have a hidden restore partition on the HD rather than supplying Windows Installation CDROMs.  Here the factory installation on the HD partition is copied as an image into the hidden one.  There may another partition containing drivers and bundled software for reinstalling in the event of problems.  Here's an example showing the Windows Primary Partition, Driver and Apps Partition and the factory set Restore Partition.

Linux drive and partition nomenclature.

    Linux (and hence Ubuntu) uses lower-case letters to assign drives and numbers the partitions within each drive.  Also, drive partitions are treated the same as directories in the filesystem.  Thus drives and partitions appear in the /dev (for device) directory.  The first letter is the drive type - IDE (PATA) drives are h, serial drives such as SATA and USB are s.  Then d for drive  Next the physical drive assigned in order - 1st is a, 2nd b etc.  Finally, the partitions are numbered sequentially in the order they were created.  Deleted partitions are not reassigned (this would cause confusion).  eg. /dev/sdb5 refers to device serial drive b (no. 2) partition 5.   Mounted partitions (and other devices) are referred to by their mount point  for data access.  This will generally be a more user friendly name and may be assigned anywhere convenient in the filesystem.

Partitioning for Installing Ubuntu

An excellent article on partitioning for Ubuntu may be found HERE

A couple of examples of partitioning using the partition editor supplied on the Ubuntu Live CD may be of interest :-

Resizing partition using Gnome Partition Editor

This process uses Ubuntu from the Live CD.

Boot from Live CD - for more info on this see Running the Live CD

Go to System > Administration > GNOME Partition Editor 

If you have more than one hard drive select the drive from the box on the top right of the dialog.  Then click on the partition to be resized to select it.  That will enable the editing options.  Here is an example,  Then click on the Resize/Move icon to display the Resize Dialog.  This shows the selected partition as a box with a slider control - a small black triangle on the right of the box.  This can be used to resize the box by clicking and dragging.  Alternatively, below the box are numerical controls to set the new size.  These show the new size and the amount of space freed up by resizing.
 Resize Dialog after setting the new size.  Click the Resize button to confirm resizing the partition.  you are then returned to the main dialog with the Apply button now available.  The changes to apply are shown in the box at the bottom while the partition layout now shows the reduced partition and the free space (in grey).  Click Apply and the confirmation dialog is displayed - Apply operations to harddisk.  Click Apply here to actually do the resizing.

Having made some empty space you can either set up partitions now of leave it until installation, when the partitioner will be run again.  In this case you can tell the installer to automatically create partitions in the free space.

See  Manual Partitioning page for installing with Manual partitioning.

Updated 9 Februay 2008