Hands on: Putting the boot in

For most people new to Linux, their biggest concern will undoubtedly be how to install it alongside Windows. Most people will understandably want to dip their toes in before wiping out what they’re accustomed to, and many may still need to use specific Windows applications even if they do decide to switch to Linux full time.

Thanks to what began with the Knoppix distribution, many Linux distributions can boot directly from CD or DVD, allowing users to try things out before committing in any way. These work entirely from CD and don’t need to modify the hard drive at all.

Although things are considerably easier than they were a few years ago, when it comes to Linux installation it’s a good idea to understand a few concepts about dual-booting if you want to go down that route. Installation programs are generally good enough, but a basic understanding is helpful to ensure you know what you are doing.

If you don’t need to dual-boot with Windows and are happy to wipe the hard drive clean, then you’ll find that a Linux installation is no more difficult than a Windows one. If anything it’s actually easier, especially as driver downloads are generally not needed at all.

Partition basics
On a PC, the hard drive needs to be split up into partitions before it can be used. A partition acts, to all intents and purposes, as a separate hard drive. Each partition can have its own file system, or indeed its own operating system. Linux does, in fact, allow you to use an entire hard drive for data without any partitions, and it even allows you to use other partitioning schemes (such as those used by Macs), but here we will concentrate on a traditional PC setup.

A hard drive can be split into four bootable partitions. These are known as primary partitions. Initially, back in the days of MS-Dos, this was the upper limit. In order to allow for more partitions, it was made possible for one of those primary partitions to be marked as an extended partition.

This itself could then be split up into any number of logical partitions. As a result, a hard drive can have one-to-four primary partitions. Alternatively, it can have one-to-three primary partitions and a number of extra logical partitions. Primary and logical partitions behave the same.

The information about partitions is stored on the master boot record, commonly referred to as the MBR. This is 512 bytes of data, stored in the first sector of the hard drive, outside of any partitions.

The MBR also holds executable code, since the PC must use this to start an operating system. If you install a copy of Windows, the traditional Dos MBR is installed. This is a simple piece of code: it checks each primary partition and whichever is marked as active is then booted.

Every partition can have executable code installed in its first sector, and this code is run on whichever partition is active. One limitation of the Dos MBR is that it can only boot primary partitions.