What Are Extended Partitions?

Extended

A 2.5" hard drive that has been opened, exposing its inner workings. This is a 500GB Western Digital Scorpio Blue hard drive with SATA connections. This 2.5" hard drive is common in laptops.

Evan Amos / Wikimedia Commons / Creative Commons 3.0

Older computers—particularly machines that boot with BIOS rather than UEFI—often cannot deploy more than four primary partitions on a physical hard disk, during the initial system boot. Given that Linux can occupy two or three, and Windows usually one or two, a hard limit of four makes multi-boot setups more difficult.

An extended partition is a primary partition that subdivides into logical partitions. Operating systems have no problem managing physical and logical partitions, so you're free to subdivide an extended partition into as many logical partitions as you need to install as many different operating systems or separate virtual hard drives as you like.