Get-WmiObject -Class Win32_LogicalDisk | ? {$_. DriveType -eq 3} | select DeviceID, {$_.Size /1GB}, {$_.FreeSpace /1GB}

# z.B. ha csak a C meghajtó érdekel
#DeviceID     $_.Size /1GB $_.FreeSpace /1GB
#--------     ------------ -----------------
#C:       99,3974571228027 0,667621612548828