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I am familiar with computers. With computers, we have BIOS. BIOS is something like memory and hard disk. It's attached to the motherboard straight. It is, for all practical purposes, like a hard disk. When we boot the computer, I bet the BIOS would start first and then we move to the operating system.

Then we got the real hard disk. We can reformat the hard disk all we want and the computer will still be useable (not bricked). That's because there is this very basic primitive operating system, namely the BIOS. Then the BIOS will read CD ROM and we can install a new operating system to the hard disk.

That's how a computer works.


Now we have Android devices.

  • I think the SD card is analogous to a hard disk. Or am I wrong here?

Then I read Android Partitions Explained: boot, system, recovery, data, cache & misc and I got even more confused.

  • So, are all the apps in the data partition? Is the SD card the whole SD card? Shouldn't data be in the SD card?
  • Also, how can Android be bricked?
  • What is the BIOS of Android?
  • So, Android has a recovery partition, boot partition, etc. Are all those on the SD card?
  • Say, I really messed up with my Android and want to start from scratch. Say, I want to format the whole SD card like I want to format the whole hard disk. Can I do that? What are the consequences?
  • Is /boot like BIOS? Is it on an SD card too (the internal one?)
  • Is internal storage the SD card?

On PC, we have memory and hard disk. It seems that in Android we have memory, and then the "hard disk" equivalent, called SD Card is also called memory again.

PC|Memory|Hard Disk
Android Devices|RAM|Memory
  • Do I get the analogy correct?
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2 Answers 2

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Can we explains android terms with its analog with PC[?]

We can try but it will restrict the expansion of our understanding since certain parts would never fit the analogy we're familiar in with desktop computing.

Take a good look at this image: aboot flowchart
Image source: Reverse Engineering Android's Aboot - by Jonathan Levin

If you want an analogy, anything before Linux kernel can be roughly called as BIOS.1

Unlike traditional Linux distributions where kernel is stored inside a filesystem, where the latter also contains files necessary for satisfactory functioning of distribution, in Android, the kernel is stored in a dedicated partition, often named /boot.

/recovery is a partition synonymous to recovery partition an OEM ships in a laptop (I suppose desktop too) to recover your primary OS (often MS Windows). In PC, the recovery can be accessed by special keys from BIOS, such as a Functional key. In Android, we have key combinations to boot the device straight into mode. We also have command-line options to instruct the device reboot into recovery mode. In that image, recovery partition should be visualized after Android BootLoader or you can say it should accompany Linux Kernel.

The Android OS is saved in a dedicated partition named system and is mounted by kernel during boot at /system. This is what you can call the factory state of the device. During OTA upgrade, the contents of this partition are upgraded.

There is fastboot mode, which is a low-level mode meant to talk to bootloader, often for the purposes of flashing the device's partitions. Fastboot should accompany Linux kernel and recovery in that image.**2

There is a partition named /cache, which you can read at What is the /cache partition? Your PC most likely wouldn't be having such a partition.

There is a partition named userdata, mounted at /data and contains user specific files. The files are so private in nature that the user itself is not authorized to read all of them. During factory reset, this partition is either partially or fully wiped out, depending upon user's preference.

Then there is a user partition which serves as a storage for user media. It is what we refer as "internal SD card". Do not use the term "internal storage" but "internal SD card" to refer to this partition. In devices containing KitKat or above Android version, there is no such physical partition but the directory /data/media/ is emulated as "internal SD Card".

There is external storage, which includes external SD card and any USB OTG drive. This is secondary class storage, meant to compensate the limited amount of free space available in "internal SD card". Boot process has nothing to with this type of storage.

There are many partitions hidden from the reach of an ordinary user. They can loosely be called as firmware or part of ROM. There is no accepted definition on what constitutes as firmware in Android, so stick with "part of ROM". Useful reading: How to list all major partitions with their labels?

Here, every physical, non-removable partition that came with the device comes under the umbrella term "Internal Storage". That said, you'll find various articles including developers.google.com where Internal storage is referred to the partition (userdata) where user's private data is stored.

You want more confusing terms. Memory is one such term. People call RAM as memory, people call internal storage as memory. Avoid this term. Use the aforementioned terms for the type of storage you want to refer. They are clear and unambiguous.

Why you can't format the inbuilt storage of Android devices just like the hard drive in PC would only invite opinion from us. Just deal with the reality that this is how it is.


1: Technically, it's the Bootloader (aka SPL, Secondary Program Loader – though that's rather comparable to a boot menu like GRUB; in the flowchart, "SBL" must be a typo). Not sure if the IPL (Initial Program Loader aka "radio firmware" aka baseband; "modem" in the flowchart) should be counted as "BIOS" – though it fulfills its functions in addressing the underlying hardware, one cannot enter it for configuration.

2: Actually, does not really have anything to do with Android specifically; it's rather an own, minimalist OS tailored for its specific purpose.


This is a community wiki. The definitions are something we do not produce individually but collectively. Improve this answer, wherever you can.

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First, RAM, hard disks, ROM, etc. are all types of memory. Also, not all Android devices have SD cards, thus they are not a necessary part of an Android file system.

PC and Android file systems are not necessarily equivalent. See the chart below for a simplified explanation of the types of memory in each system and their uses.

PC Android
Memory Type Use Memory Type Use
RAM Volatile memory used while the device is running, erased when the computer is shut off RAM Volatile memory used while the device is running, erased when the computer is shut off
ROM Where BIOS (commands that are run on initial power-up) is stored ROM Where Bootloader (similar to BIOS) and Operating System are stored. This memory is what is flashed when you install a new OS and what is corrupted when the phone is bricked
Hard Disk Where Operating System and most data, including programs, is stored Internal Flash Memory Where all user and app data is stored. Each app has its own section within this memory that it can use to store data, special permission must be given for an app to access data outside of its partition
External Optional storage space of programs and data SD Card Optional expansion of Internal Flash Memory

Original chart

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  • You sure the table is correct? Got sources? So the operating system is in the "BIOS" of the android? Also there is no way data and app is stored in RAM. RAM it turned off when device is turned off. If I restart my android my app is still there.
    – user4951
    Feb 15, 2016 at 2:54
  • Physically, is internal memory and ROM on the same "organ"?
    – user4951
    Feb 15, 2016 at 2:56
  • If you notice, there is a division in the middle of the table. The left half is regarding Pc and the right regarding Android. So, no the OS is not in the BIOS of the Android and "data and app" is not stored in RAM. Everything is turned off when the device is turned off but the internal clock, but RAM is wiped. Feb 15, 2016 at 2:57
  • Again, please relook at the chart, noticing the division in the center. Internal Memory and ROM are two different chips. Feb 15, 2016 at 3:03

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