Windows system can only be installed on primary partitions, there's always one primary partition in one disk, C Drive, so when you want to extend primary partition, it must be the system partition you want to resize. Data partition always set to logical partition, free space with large capacity always stays in logical partition; when low disk space happens to primary partition, the simplest way is to extend it with free space from logical partition.
"Hi, I'd like to extend the partition of my OS (primary partition). So, I reduce another partition (logical partition) containing DATA. This new free space is only available for logical partition and I can't extend my primary partition with it. Is-it possible to merge free space of logical partition with a primary partition?"
User above would like to extend primary partition with free space from logical partition without DATA loss, so Windows Disk Management cannot be the possible solution, even backup logical partition before deleting it indeed is a workout for this case, but still no, nope, not what he wants, I think all he wants is just simply move free space from one to another.
Macrorit Partition Expert is designed for this situation; you can freely move free space from logical partition to primary partition without data loss.
"Hi. I'm running Windows 8. I have a 1TB HDD I've got split into two. A primary partition and a logical drive. I'm trying to add some of the free space to the primary partition, but it will not let me extend the primary partition, nor delete the free space. The only thing I can do is delete the entire logical drive, but I do not want to do that. Help!"
It seems that Shrink Volume in Disk Management cannot meet common needs on system partition extending or any partition resizing in later use. It is not work with Extend Volume but only for creating unallocated space and decrease the particular volume. Try Partition Expert, and you don't have to delete the entire logical drive, and you have the primary partition extended at last.
Steps to move free space from logical partition to primary partition:
After it's done, you have moved free space from logical partition to primary partition without losing original data in both partitions. Of course, you can do move free space form primary partition to logical partition vice versa. Resize Move Volume is the powerful function in Windows disk partition managing. Use it well and you'll have a performance improved system.