Android File System and Directory Structure Explained


Android-file-systemMost people are familiar with the file layout on Windows and are happy navigating the Windows file System.

Windows uses a drive letter for each physical drive or partition.e.g. C: drive

Note: A Physical drive will have at least 1 partition but can have more than one. This is true for both Windows and Android.

What is a Disk Partition? – Disks can be subdivided into smaller disks called partitions. Partitions appear and can be used as if they were separate physical disks.

If you insert a USB drive into your windows machine in shows up as a disk with an assigned drive letter.

windows-disks

Although windows shows a disk icon the disks could be partitions of a single physical disk.

Each disk partition has a root directory which contains files and folders (directories).

The root of the C drive is C:\ and of the F drive is F:\ etc

Android File System Structure

Android uses the Linux file system structure which has a single root.

The diagram below shows the structure

Android-File-System-Structure

The system partitions and directories are protected and unless your device is rooted you don’t normally have access to these although some file managers will display them.

Physical disks and partitions appear under the root as a directories , and do not have a drive letter as in Windows.

Android doesn’t normally come with a default file manager, and so you will need to install a file manager App like Astro file manager, to locate and manage files and folders.

The sdcard and ext-sdcard Partitions

The sdcard partition is the main storage area for user data and files. It also contains App settings and data.

The sdcard partition exists even though you may not have an external sd card.

It is the internal partition.

If you open the sdcard directory you will see something like this:

android-sdcard-directory

Note: partial listing only

These files and directories contain your pictures,films,downloads etc as well as App data and settings.

You can view these files from your PC by connecting your device to a PC using a USB cable.

You can also transfer files between your device and a PC using this method.

The ext-sdcard partition will only be visible if your device supports external storage, usually using a microSD slot.

External sd cards use either the FAT,FAT32 or exFAT file system formats.

Most devices support FAT and FAT32, but support for exFAT is limited.

The choice of file system is governed by the partition size as follows:

Card Type

Card Type File System

Max Capacity

SD FAT 2GB
SDHC FAT32 32GB see Note
SDXC exFAT 2TB

Note: Windows format size limit of 32GB. Can be larger but need to format using external tools. Windows XP could fomat FAT32 Volumes upto 128 GB

Android File Associations

Just as with other operating systems like Windows, Android will use an App to open a particular file type,denoted by the extension.

For example if you try to open a pdf file it will normally use Adobe reader (if installed) to open the file.

To open a file you will normally need to located the file using a file manager.

Just press the file to open it.

select-files
If the file type doesn’t already have an App associated with it you should be prompted to choose between the available Apps.

set-default-app-android

The option to always use that App sets it as the default App for that file type.

If you set it as the default App you will not be prompted again unless you remove the association.

To remove an association you need to remove it from the App itself.

So if the pdf files open with adobe reader and you want to change that:

  1. Go to Settings>Apps>Select Adobe reader,
  2. Then go to the Launch by default section
  3. and Clear defaults

clear-file-associations-android

The next time you try to open a pdf file you will be promoted to choose an App.

Android File Managers

If you search the Google play store you will find many file managers.

Which App is the most suitable depends on what you want to do. You should bear in mind that more features/functionality isn’t always better.

File managers like ESF have lots of functionality including:

  • Built in FTP client
  • Task Manager
  • Cloud storage client
  • etc

However for many this is a bit of an overkill, and so you might consider installing one of the simpler file managers like file manager and Astro file manager.

See my tutorial using the Astro file manager.

File Downloads

When you download a file using Google chrome or another browser App the file it is stored in the download directory.

You can access the directory contents through a shortcut in the Apps folder (if provided).

android-download-app-shortcut

You can also use a file manager to locate it the folder called download. It is under your primary storage (called sdcard)

android-download-directory

Summary

Android uses the Linux File and Directory Structure which consists of a single root.

All drives and partitions are displayed as directories in this tree like structure.

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