Mobile device users are often faced with the need to update or replace system software, but are confused about the terminology. The question of what exactly the firmware on Android is called has several layers of answer, depending on the context of use and technical nuances. In a broad sense, this concept covers an operating system with a whole set of drivers and services, but technically literate users also share system image the flashing process itself.
Understanding the difference between a standard over-the-air update and manual installation of a system image is critical to the security of your device. Erroneous actions when working with low-level software can turn a smartphone into a “brick,” so you first need to understand the nomenclature of files and methods for installing them.
In this article we will take a detailed look at what file formats are used for firmware, how official software differs from modified versions, and how to correctly identify the type of firmware for your phone model. Knowing these basics will allow you to avoid fatal errors when restoring your device.
Terminology: ROM, Firmware and System Image
Among Android enthusiasts, the term “firmware” is often replaced by the English word ROM (Read-Only Memory), although technically this is not entirely correct. Historically, system software was written to non-volatile read-only memory, hence the name. Today, under Custom ROM we understand any modified version of the operating system created by third-party developers.
Official distributions from manufacturers (Samsung, Xiaomi, Pixel) usually do not call ROM in the user environment, but are simply called “software update” or “system image”. The files of such updates have specific extensions and are signed with the manufacturer’s digital keys to protect against unauthorized intervention.
The key difference is the level of access: standard firmware blocks the ability to change system partitions, while custom builds often require unlocking the bootloader. This gives the user full control over the device, but voids the warranty and may disrupt the operation of banking applications.
⚠️ Attention: Installing unsigned system images on devices with a locked bootloader can lead to an endless reboot (bootloop) without the possibility of recovery through standard methods.
For beginners, it is important to remember that a firmware file is not just an archive with data, but a complex structure containing the Linux kernel, hardware drivers and a user interface. An incorrect kernel version may cause the camera or Wi-Fi module to stop functioning even after successful installation.
Firmware file formats and their purposes
Various manufacturers and installation methods dictate the use of specific file formats. Understanding extensions helps determine which tool to use for installation. For example, files with the extension .zip are most often intended for installation through Recovery mode.
Devices based on MediaTek processors often use images in the format .img or archives .pac, which are flashed through specialized software on a PC, such as SP Flash Tool. In the Qualcomm ecosystem, files .mbn and .elfare common and are included in comprehensive packages for the QFIL tool.
Always check the checksum (MD5 or SHA-256) of the downloaded firmware file before installation. A file damaged during loading can damage the device.
The most universal format for custom firmware remains a ZIP archive containing an installation script and a set of partition images. When flashing firmware via ADB (Android Debug Bridge), commands are often used that work directly with files .img, writing them to the corresponding block memory devices.
fastboot flash boot boot.imgfastboot flash system system.img
fastboot reboot
These commands demonstrate the process of manually recording images of the boot partition and system. A misspelled partition name or file path can overwrite critical data such as IMEI or display calibration.
| File format | Device type | Installation method | Risks |
|---|---|---|---|
| .zip | Universal (Custom ROM) | Recovery / TWRP | Medium (requires unlocking) |
| .tar /.tar.md5 | Samsung | Odin | Low (official method) |
| .img + scatter | MediaTek | SP Flash Tool | High (risk of losing IMEI) |
| .xml +.mbn | Qualcomm | QFIL / EDL Mode | Critical (authorization required) |
The choice of firmware format depends solely on the processor of your device and the mode in which it can be loaded (Fastboot, Download, EDL).
Official and custom versions of Android
Official firmware is developed by device manufacturers and are optimized for specific hardware. They ensure stable operation of all components, including the camera, sensors and communication modules. However, support for such versions is often limited to two to three years, after which security updates cease.
Custom firmware, such as LineageOS, Pixel Experience or Resurrection Remixare created by a community of enthusiasts. Their main advantage is the ability to get the latest version of Android on an old device that the manufacturer has no longer updated. In addition, they offer advanced interface customization options.
However, custom assemblies have their drawbacks. First, they may be unstable on some models due to lack of access to the manufacturer's original drivers. Secondly, the use of such systems often disrupts the operation of applications that require checking the integrity of the environment, for example, banking clients or Google Pay.
When choosing between stock and custom, it is important to assess your needs. If you need a reliable phone for calls and work, it's better to stick with the official version. If you are a geek and want to get the most out of the device, experiments with Custom ROM may be justified.
Preparing for installing the firmware: Checklist
The flashing process requires careful preparation, as it irreversibly deletes all data from the device. Before starting any manipulations, you must create a complete backup of your contacts, photos and important documents in cloud storage or on your computer.
A critically important step is unlocking the Bootloader. On many modern smartphones (Xiaomi, Huawei, Sony), this procedure requires waiting from 3 to 7 days after submitting an application on the manufacturer’s official website. Without an unlocked bootloader, installing third-party software is impossible.
☑️ Preparing for flashing
You also need to make sure that the correct drivers for your device are installed on your computer. The lack of drivers in the Windows Device Manager may result in the PC simply not seeing the phone in firmware mode, which will interrupt the process at the very start.
⚠️ Attention: The procedure for unlocking the bootloader on most devices automatically performs a full data reset (Wipe Data). Make sure that you have saved everything important before starting this process.
The process of flashing firmware via Recovery and Fastboot
There are two main ways to install firmware manually: through Recovery mode and through Fastboot mode. Recovery mode, especially custom mode (for example, TWRP), allows you to install ZIP archives directly from the phone's memory or SD card, which is convenient for updating the system without a PC.
Fastboot mode involves connecting the device to the computer via USB and sending commands via the console. This method is more reliable when restoring “bricked” devices, as it allows you to repartition the memory and write partition images directly, bypassing the standard boot system.
When using TWRP, it is important to properly perform partition cleaning (Wipe). It is generally recommended to format the Data, Cache and Dalvik/ART Cache partitions. However, you do not need to format the Internal Storage partition if the firmware file is located there.
What is Dirty Flash?
Dirty Flash is installing a new firmware version over the old one without completely clearing the data. This saves time on setup, but can lead to errors and unstable operation of the system if the file structure has changed.
After the image recording process is completed, you must run the reboot command. The first launch after the firmware can take from 5 to 15 minutes, as the system optimizes applications and creates a cache. Interrupting this process with the power button is unacceptable.
Possible problems and solutions
Even if you carefully follow the instructions, errors may occur. The most common problem is “Bootloop”, where the phone endlessly reboots at the logo. This is often solved by reinstalling the firmware with full data clearing (Full Wipe).
Another common error is lack of connection or broken IMEI. This happens if the NVRAM or EFS partition was erased when flashing devices on MediaTek. Restoring IMEI is a complex procedure that requires a dump of this partition, made before the problems.
If the device does not turn on at all and does not respond to buttons, it may have gone into deep protection mode (EDL for Qualcomm or Download for Samsung). Exiting this state often requires the use of authorized service center accounts or special repair boxes.
⚠️ Attention: Recovery menu interfaces and Fastboot command sets may differ depending on the Android version and manufacturer. Always check the latest instructions for your specific model on the relevant forums.
Most errors during firmware occur due to a mismatch between the Recovery version and the firmware version or the use of a damaged image file.
FAQ: Frequently Asked Questions
Is it possible to return to the official firmware after installation custom?
Yes, it is possible. To do this, you need to find the official firmware image (Stock ROM) for your model and install it through Fastboot mode or a special tool from the manufacturer (for example, Odin for Samsung or Mi Flash for Xiaomi). This will also restore the warranty if the bootloader is locked again.
Will the warranty be void after unlocking the bootloader?
In most cases, yes. Unlocking the bootloader and obtaining root access is a violation of the license agreement and often leads to denial of warranty service, especially if the problem is software related. Some manufacturers (for example, Xiaomi) allow you to officially unlock the bootloader, but this will still void the software warranty.
Is it safe to use banking applications on custom firmware?
The default is no. Banking apps and Google Pay use the SafetyNet service (or its replacement, the Play Integrity API), which checks system integrity. This check does not pass on custom firmware with an unlocked bootloader. However, there are methods for hiding root access and bootloader status (via Magisk) that can bypass this protection, but this is an arms race with bank developers.
What to do if the phone is not visible to the computer in Fastboot mode?
Try replacing the USB cable with a high-quality original one, using a different USB port (preferably USB 2.0 on the back of the PC) and reinstall ADB/Fastboot drivers. Also make sure that there are no unknown devices with an exclamation mark in the device manager.
How to find the exact model of the device to search for firmware?
The exact model can be found in the menu Settings → About phone. Look for the “Model number” line. For more detailed information, including the region code, you can use applications like Device Info HW or enter the code in the dialer (does not work on all devices). data-i="122">Firmware file formats and their purpose ##4636## in the dialer (does not work on all devices).