Windows: file system

Files, directories and volumes

Windows (like many other) file systems organize data on hard disks and devices with the concept of files and directories.

In addition, Windows supported file systems also have the concept of volumes. A volume is a container for a file system.

Paths

A path consists of a series of directory names that optionally ends with a file name. The directory and file names are separated by a back slash:

\dirOne\dirTwo\dirThree\filename.ext

The WinAPI I/O functions convert a forward slash to back slash except when the special \\?\ prefix is used.

Maximum length of path names

See also the value of LongPathsEnabled under the registry key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\FileSystem.

Reserved file names

Some file names are reserved and cannot or should not be used for actual files

CON (The console)
PRN (Printer)
AUX
NUL (null device, compare with /dev/null on Unix/Linux)
COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9
LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, LPT9 (Parallel ports)

These names should not even be used with filename extension such as NUL.txt.

Prohibited characters in file names

The following characters are not allowed in file and directory names:

<, > (Redirection operators)
: (Stream name separator)
"
/, \ (Path separator (also forward slash?))
?, * (Wildcards)

Determining free and used space on local file systems

A quick way to determine the free and used space on local file systems with PowerShell is

PS C:\> get-psDrive -psProvider fileSystem

Alternatively, it can also be queried with

get-wmiObject -class win32_logicalDisk |                       `
  select-object                                               `
     deviceId,                                                 `
     @{L=' Free (GB)';E={"{0,10:N1}" -f ($_.freeSpace /1GB)}}, `
     @{L='Total (GB)';E={"{0,10:N1}" -f ($_.size      /1GB)}}

Determining file system type

The file system type (for example NTFS or FAT32 can be determined with fsutil.exe)

Showing drives on the command line

C:\> wmic logicaldisk get deviceid,volumename