How do you partition a disk without losing data?
In a situation where there is only one hard drive in the computer, dividing the disk into individual disk partitions is almost a necessity. The first partition – the system partition – should contain the operating system and installed programs. The second partition – the data partition – should contain data only. The reason is simple: if you lose the system partition (usually due to an operating system crash), your data stored on the data partition will remain intact.
Disk partitioning with Windows 8, 10 (without data loss)
1) Right-click This PC (either on the desktop or in the Control Panel)
2) From the menu, select “Manage”
3) Then, select “Disk Management” from the menu on the left
4) Right-click the relevant disk partition and select “Shrink”
5) After shrinking the partition, you can assign the resulting space to another partition.
Disk partitioning with Windows 8, 10 using Acronis Disk Director software (without data loss)
1) Launch Acronis Disk Director
2) Right-click the relevant disk partition and select the split option
3) Follow the instructions in the disk partitioning wizard
Note:
The trial version of Acronis Disk Director only allows changes up to 100 MB.

