Many developers have reported that the legacy SUBST command, which worked flawlessly in Windows 7, fails to create virtual drives in Windows 10. When executing:

SUBST R: "C:\BlahBlah\XXX\YYY"

The expected R: drive either doesn't appear in File Explorer or disappears after reboot, even when running Command Prompt as Administrator.

Windows 10 introduced several security and architectural changes that affect SUBST behavior:

• Session isolation in modern Windows versions
• UAC virtualization differences
• Explorer.exe process separation

Method 1: Permanent Mapping via Registry

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\DOS Devices]
"R:"="\\??\\C:\\BlahBlah\\XXX\\YYY"

Method 2: PowerShell Alternative

New-PSDrive -Name "R" -PSProvider FileSystem -Root "C:\BlahBlah\XXX\YYY" -Persist

For programming scenarios requiring stable virtual drives:

// C# example to create persistent mapping
using Microsoft.Win32;

RegistryKey key = Registry.LocalMachine.CreateSubKey(
    @"SYSTEM\CurrentControlSet\Control\Session Manager\DOS Devices");
key.SetValue("R:", @"\??\C:\BlahBlah\XXX\YYY");
key.Close();

Remember that modern Windows handles drive mappings differently:

• Mappings are per-session by default
• Require elevation for system-wide changes
• May conflict with OneDrive/cloud storage integrations

Many developers who've recently migrated to Windows 10 report the SUBST command no longer functions as expected. Where previously you could simply execute:

SUBST R: "C:\\Projects\\React\\Build"

The virtual drive would immediately appear in File Explorer. Now, the command appears to execute successfully (returns no errors) but the mapped drive fails to appear.

After extensive testing, I've found these reliable methods:

Method 1: Registry Modification

REG ADD "HKLM\\SYSTEM\\CurrentControlSet\\Control\\Session Manager\\DOS Devices" /v "R:" /t REG_SZ /d "\\??\\C:\\Projects" /f

Requires admin privileges and a reboot. This directly writes to the DOS devices registry key that SUBST normally modifies.

Method 2: PowerShell Alternative

New-PSDrive -Name "R" -PSProvider FileSystem -Root "C:\\Projects" -Persist

Works immediately without reboot. The -Persist flag makes the mapping survive reboots.

The underlying issue stems from changes in Windows 10's session isolation and virtualization security model. When you run SUBST:

• Command Prompt: Creates mapping only for current session
• Explorer.exe: Runs in different session by default
• Group Policy: May block non-admin drive mappings

For developers using build tools or IDEs, consider these alternatives:

:: Batch file solution
@echo off
if exist R: subst R: /d
subst R: "C:\\Code\\Angular"
start "" "C:\\Program Files\\Microsoft VS Code\\Code.exe" R:

Or for Node.js projects:

// package.json
"scripts": {
  "mapdrive": "powershell -command \"New-PSDrive -Name 'R' -PSProvider FileSystem -Root (Resolve-Path '../dist') -Persist\""
}