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I want to allocate more space for my GPT drive, using windows 10.

Is there any way to convert my drive which is in GPT format into MBR, so that I can allocate space for partition D?

I really don't want to reformat my drive because my OS and other important software are in there. I also don't want to use any third party software that are costly since I am a student. Any help will be appreciated.

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    Why do you think MBR will let you use more disk space? Generally it allows less. – user1686 Aug 28 '18 at 5:58
  • @grawity I might have mistaken disk and partition formats don't I? But I really want to allocate some space to my drive C, Window 10 updates is consuming most of my disk space that I fear my current allocated space wont suffice for future updates. – Mr.J Aug 28 '18 at 7:32
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    @MrJ: More than that, I think you're mistaking the cause of the problem in general. Where is the space currently? How does GPT prevent you from using it? Can you provide a screenshot of diskmgmt.msc with your drive visible? – user1686 Aug 28 '18 at 8:01
  • @grawity the space is at drive D, I want to allocate some space from drive D to drive C so that I can acquire more windows update in the near future, I am running low of disk space in drive C, now I currently have 40GB of space. – Mr.J Aug 28 '18 at 8:27
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    @phuclv: Yes, but I would say that being unable to use above 2 TB of one's shiny new 8 TB disk due to MBR limits is a more practical concern for most people than being unable to squeeze out the last ~4 kB of space due to GPT placement. – user1686 Aug 28 '18 at 12:14
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the space is at drive D, I want to allocate some space from drive D to drive C so that I can acquire more windows update in the near future, I am running low of disk space in drive C, now I currently have 40GB of space

Well, your disk's partition table type is mostly irrelevant here. If you have two partitions of certain sizes in certain places, and convert the disk between GPT and MBR, you'll still have two partitions of the same size in the same place.

First you need to shrink the D: partition. You can do this from within Windows diskmgmt.msc, just right-click the partition in the lower pane and select "Shrink", which will take several minutes.

This will always shrink towards the 'beginning', which means you end up with {C:, D:, free space} in that order. So next you need to shift D: with all its data towards the 'end' of the disk.

The reason for needing to move all data is that neither MBR nor GPT allow partitions to be composed of several chunks: they must always be a single continuous block of disk space. If you really needed a bit of partition C:, then partition D:, then another bit of partition C:, you'd need a technology such as LDM on Windows (aka "dynamic disks") or LVM on Linux.

But although enabling LDM (i.e. converting to dynamic disk) is relatively painless, I would not recommend it, partly because I haven't heard good things about its performance compared to regular mode (though this may be specific to its 'RAID' modes). So instead of enabling something that may make the system slow forever, I'd rather recommend a one-time partition move.

To do this, pick up a Linux live CD (e.g. Ubuntu Live or GParted Live) and start GParted within it. Select the D: partition and move it rightwards. This will take a long time (approx. 30 seconds per GB) so it really needs AC power the whole time.

When the move is done and you have {C:, free space, D:} you can quickly expand the C: partition via diskmgmt.msc from Windows again.


(It's possible to do the shrinking and expanding via GParted as well, but as it's a technically complex operation you might trust Windows' own tools more.)


As for literally converting the disk's partition table type: It's possible but might get complicated, due to Windows being a bit picky about disk/firmware combinations – it refuses to install to MBR disks in UEFI mode, so I don't know whether an existing installation would properly boot from an MBR disk in UEFI mode if it found itself converted.

So, although the disk conversion itself is easily done using gdisk (again ideally from within a Linux live disk), afterwards you will most likely need to delete the old EFI System Partition and use a Windows install/recovery disk to install a BIOS-compatible bootloader (and matching system partition) in its place.

Tutorials for converting Windows systems the other way around (MBR/BIOS to GPT/UEFI) exist in various places and could be adapted easily.

Regardless, converting a disk from GPT to MBR partitioning will do nothing for your disk space problem.

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I don't think converting from GPT to MBR will gain you a whole lot of disk space. In addition, if you have Windows 10 installed using UEFI, then GPT is mandatory. MBR can only be used with BIOS.

However, Windows does not supply any standard way to convert without data-loss. You would absolutely require a third-party product.

See this guide for using the free AOMEI Partition Assistant. :
How to Convert GPT to MBR or Convert MBR to GPT Disk?.

While in theory it is possible to convert GPT to MBR without data loss, I would still recommend to backup the disk as a disk-image, just in case.

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