How to Fix the Steam Stuck on Allocating Disk Space on Windows 10

Steam is most PC gamers’ window to the gaming world. Microsoft may own Windows, but Valve owns gaming on Windows thanks to the all-powerful and super-convenient platform. But even the best pieces of software can have their bad days, and Steam – being the complex beast that it is – could fail to open for you for any number of reasons.

Here we run through the most common causes for Steam not opening on your PC and our solutions.
Solution 1: End the Steam Process in Task Manager and Run it as an Administrator
Violently ending the Steam process during the installation seems to be a great way to resolve the problem, according to other users who have experienced the same problem. Ending the task and reopening Steam and the installation managed to resolve the problem for many users so make sure you try it out as well.
1. Press Windows Key

+ R combination to open the Run box. Type taskmgr.exe in the textbox without the quotation marks and click OK to open the Task Manager.

2. Click More details inside to expand it. Navigate to the Details tab and click the Name column to sort the list of tasks in alphabetical order.
3. Scroll down until you reach the Steam.exe entry in the list. Left-click it and click the End task button in the bottom right part of the window. Repeat the process for all entries if available.

4. Open up Steam’s installation folder, locate the installation folder manually. By default, it should be:
C:\Program Files (x86)\Steam

5. Locate the Steam.exe file inside, right-click its entry and choose Properties from the menu which will appear after right-clicking. Navigate to the Compatibility tab inside Properties.
6. Under the Settings section at the bottom, make sure you place a checkmark next to the Run this program as an administrator. Confirm the changes you have made by clicking the OK button inside.

7. Reopen the Steam client by double-clicking its icon on the Desktop or by searching for it. Check to see if the installation finishes without getting stuck on the Allocating disk space message!
Solution 2: Clear Download Cache
The most obvious cause of this problem is that Steam got stuck trying to manage its download cache files. This cache can be cleared easily from within the client so make sure you try out this simple method before moving on to the more complicated ones. Follow the steps below to clear the download cache in Steam.
1. Open up your Steam client by double-clicking its shortcut on the Desktop. An alternative is to simply search for it in the Start menu or by clicking the Search/Cortana button next to it.
2. This method can be performed even when the installation is already running and the Allocating disk space message is being displayed. Click the Steam button at the menu bar at the top right part of the window and choose the Settings option from the context menu which will appear.
3. Navigate to the Downloads tab and check the bottom of the screen for the Clear Download Cache Click it before clicking OK. In the Steam window, click the Steam button again and click Exit to quit Steam completely.

4. Then select OK to confirm

5. Reopen the client and the download/install should now finish without any problems!
Solution 3: Change Download Region
The Steam content system is divided into geographical regions. The Steam client automatically detects its current region and uses content servers located in that region.
Sometimes, servers in a specific region may be slow or overloaded, leading to Steam disk write error while downloading. You can switch to a different download region, using another set of content servers to have a try.

Please go to Steam > Settings > Downloads > Download Region. You may need to test several regions other than your own.
Solution 4: Delete the 0KB File
This solution is provided by a Reddit user and many users rate it useful. In short, he just solved this issue by going into Program Files (x86)/Steam/steamapps/common and simply deleting a file titled "Fallout" that was 0KB in size. When he re-launched the game, Fallout 4 loaded up perfectly. This solution might also be useful when updating similar games
Solution 5: Remove Write Protection
When a disk is write-protected, you're unable to modify the formatting and writing. This is another possible reason for the Steam disk write error. Please make sure the directory of Steam is NOT read-only. Then right click your Steam launch icon and click Run as administrator.
But if the disk is already written protected, you can simply clear write protection and remove the error using command.
1. Run Command Prompt as an Administrator.

2. Then type these commands one by one and press the Enter key after each:
diskpart
list disk
select disk # (# is the number of the hard drive with which you're getting the disk error)
attributes disk clear readonly
remove disk read only attributes