$z="$env:SystemDrive\zero.fill"; $fs=[IO.File]::Open($z,'Create','Write','None'); try{ $b=New-Object byte[] (1MB); while((Get-PSDrive -Name $env:SystemDrive.TrimEnd(':')).Free -gt 300MB){ $fs.Write($b,0,$b.Length) } } finally{ $fs.Close() }; Remove-Item $z -Force