• Windows
  • Guides

Your C drive is full and D has 800 GB free. What to do about it

Two drives, one of them useless, and the options ranked by how well they work. Including the one that is usually wrong.

5 min read

This is the most common Windows storage situation there is: a small fast SSD as C, a large drive as D, and everything piling up on C because that is where Windows puts things by default.

The options, best first

  1. Move user folders. Documents, Pictures, Videos and Downloads each relocate through Properties, Location, Move. Supported, permanent, and applications follow.
  2. Point games and large software at D. Steam library folders, per game install locations, and installers that ask.
  3. Move caches that have a setting. Docker, npm, pip, media editors and more each allow a path.
  4. Change where new content saves. Settings, System, Storage, Advanced storage settings.
  5. Extend C into free space on the same physical disk, if that is the actual layout.

The option that is usually wrong

Extending C using space from D is only possible when they are partitions of the same physical disk and the free space is adjacent. If D is a separate drive, no amount of Disk Management will merge them, and tools that claim to combine drives into one volume are creating a spanned volume, which means losing either drive loses everything on both.

Checking what you actually have

Get-Disk | Select-Object Number, FriendlyName, @{n='SizeGB';e={[math]::Round($_.Size/1GB)}}
Get-Partition | Select-Object DiskNumber, DriveLetter, @{n='SizeGB';e={[math]::Round($_.Size/1GB)}}

If C and D show different disk numbers, they are different physical drives and extending is not an option. If they share a number, they are partitions and Disk Management may be able to help.

The shortcut people reach for

Moving a folder to D and leaving a junction behind works and has real risks, covered in moving programs to another drive. For caches it is reasonable; for installed software it is not.

What must stay on C

Windows, the page file (unless you have a genuine reason and a second physical disk), and anything written to constantly during a build. Everything read occasionally belongs on the larger drive.

Common questions

Can I move space from D to C?

Only if they are partitions on the same physical disk with adjacent free space. If they are separate drives, no tool can merge them safely, and spanned volumes mean losing one drive loses both.

How do I make Windows use my D drive?

Move user folders through Properties, Location, Move; point game launchers at D; set cache locations in the tools that allow it; and change where new content is saved in Settings.

How do I tell if C and D are the same disk?

Run Get-Partition in PowerShell and compare the disk numbers. The same number means partitions on one disk; different numbers mean separate physical drives.

Is it safe to move Program Files to another drive?

No. Programs write registry entries and absolute paths at install time, so moving the folder breaks them. Uninstall and reinstall on the other drive instead.

Read next