Procedure to extend Windows System Partition with non-adjacent or non-contiguous unallocated Free space

Scenario: 

• You have a single physical disk having System Partition, Data  Partition and some unallocated free space at the end. 
• Your System Partition gets filled and you want to extend it by adding the free unallocated space available on the same physical disk.
• Windows Disk Management tool doesn’t enable the “Extend Volume” option (i.e., “Extend Volume” option is greyed out as shown below)
• This behavior remains same irrespective of Unallocated space is just RAW of Formatted as FAT32/NTFS volume.

Cause:

• In order to be able to extend a volume, the Unallocated free space must be on the same disk, and it must be adjacent/immediately follow the volume which you want to extend
• In particular the logical drives, boot, or system volumes can be extended only into contiguous space.
• In case of other volumes, you can extend them into non-contiguous (non adjacent) space, by converting the disk to dynamic disk.

Solution:

• You need to get the free unallocated disk space adjacent to the system partition then you can extend the System Partition to include the free space.
• You can use Windows Built-in command diskpart to manage the  volumes and get the free space adjacent to System Partition and then extend it.
• More better is to use a third party Partition Management software which provide rich GUI options

• EaseUS Partition Manager, allows you to move unallocated space adjacent to System Partition and then extend the System Partition.  Note: always use latest version of the Partition Manager software as I have encountered errors and failure with older version of the software.  However, the latest version jus did the job fine. 
• EaseUS Partition Manager, I didn’t use move partition option, instead I used below steps:

• I extended my second partition to include  the free unallocated space.
• Resized the second partition to free up space at its beginning.
• Then allocated that free space before the second partition to my System Partition
• That’s all, job done.  Upon simple refresh, I got my system partition (the C drive) space extended.

References:

• How to extend a partition with a non-adjacent unallocated disk space
• Disk Management Cannot Extend Volume to Unallocated Space
• How to add disk space to C drive or system partition