When booting, the BIOS of a PC looks at the first sector of a disk (the Master Boot Record, MBR) and validates that a boot record is found. Then control is passed to the boot loader in this structure which in turn reads more blocks from the disk, using the BIOS i/o routines. This is the reason for partitioning - the BIOS reads the blocks and its routines define the layout of hard disks.

Current disks on PCs can be partitioned with primary partitions and additonally extended partitions. A minimum of one primary partition is required and a maximum of four primary partitions per disk is allowed. As a method to handle disk partitions more flexible there is also the option to create one extended partition per disk at the cost of losing one primary partition. The extended partition itself is unusable for file systems. Instead is used as a container to overcome the limitation of primary partitions: within an extended partition logical partitions can be created which in turn can be used. The BIOS normally requires that at least one primary partition is present which is tagged active and contains the OS (This is true at least for older operating systems - Linux as a clever OS has a number of boot managers which are able to boot the kernel even from logical partitions). Thus, many operating systems tend to configure the disk as one partition and use its space for all purposes.

Not to mention multi-boot configurations, this solution is somewhat suboptimal: An operating system has to perform many different tasks, requiring different use of resources - disk space in our case. There is e.g. swap as well as storage for temporary files, applications, and there can be numerous more, depending on the type of system. All of these should be handled spearately, primarily to avoid data loss which could occur if there were only one file system and this would be damaged but also to gain a finer level of control. Therefore often disks are configured with primary and extended partitions, and partitioning schemes for various purposes are a part of virtually every Linux installation guide. This topic also leads to lengthy debates since all of these schemes share a common problem: they can't be changed after installation without massive impact on the operating system, usually requiring a fresh installation.

This is where LVM comes into play. It allows to handle disk space very flexible not only at installation time but also anytime later. But for this we have to adopt some new ideas. Basically the BIOS limitation of four primary partitions can't be overcome but in the effect this is what happens. We will now have a look at the terms of LVM