Extended partition is different from primary partition. An extended partition cannot store any data but it can contain multiple sub-partitions inside it, or in Windows it is referred as logical drive. Extended partition is needed to overcome the limit of MBR disk, which only allow 4 primary partitions created. Creating extended partition in Windows is done automatically when creating the fourth partition, but it can also be done manually on other partitions as well.
Manually Creating Extended Partition in Windows
The step by step below will demonstrate how to create extended partition using command prompt and Windows Disk Management snap-in.
1. Ensure there is unallocated space
Open Disk Management console, see if there is unallocated space on the disk where the extended partition will be created. In this example below, both Disk 0 and Disk 1 has unallocated space.
From the screenshot above, we can see that there is no need to manually create extended partition on Disk 0 because it already has three primary partitions in it and the fourth will be automatically created as extended partition. Therefore, the further steps on the example are going to focus on Disk 1.
2. Open command prompt and run diskpart utility
Command prompt needs to be run with administrator privilege. Right click and choose Run as administrator.
On the command prompt, type diskpart and press enter. Notice that the prompt will be changed as shown in the screenshot below
3. Selecting the disk
Now run command select disk X, where X is the disk number where extended partition will be created. As explained in the first step, in this example the extended partition will be created in Disk 1, and the command in this example will looks like as in below screenshot:
Notice that Windows will respond the command with a confirmation of the disk selection.
4. Creating extended partition
The extended partition can be created with the command create partition extended size=XXXX. The XXXX represents size specified in MB, where 1024 MB equals to 1 GB. The size parameter is optional, and if it is not used then the extended partition will takes up all the remaining unallocated space. In this example, the extended partition will be created in 1 GB size.
After running the command above, notice on the Disk Management that a new partition has been created with a dark green border line, indicating that it is an extended partition.
Right now this partition cannot be used to store data until a logical drive is created in it.
5. Creating logical drive inside an extended partition
On Disk Management, right click on the extended partition area and select New Simple Volume
And the rest of the steps are the same as creating a primary partition or volume.
Working with Extended Partition and Logical Drive in Windows
The result can be verified from the Disk Management console. In the screenshot below, we can see that logical drive and it has a blue color indicating that it is different from the primary partition which are in dark blue color. Logical drive is created on an extended partition area, where the area is marked by the dark green border line.
From performance point of view, there is almost no difference between drives created as primary partition and logical drives created on extended partition. But, keep in mind that Windows can only be run on a primary partition. By default, there is no way to convert from primary partition to extended partition and vice versa, except by using third party software.
Nowadays, administrator can avoid creating extended partition in Windows by using GPT disk instead of MBR, however it is still nice to know how to deal with extended partitions and logical drives.