Understanding Android Primary & Secondary Partitions

Understanding Android Primary & Secondary Partitions

Introduction

The Android system consists of various partitions, many of which function as primary or secondary storage areas. These secondary or reserve partitions are vital, often serving as backups for essential system sectors. Common examples include:

• SYSTEM_A, SYSTEM_B

• BOOT1, BOOT2 (also known as PRELOADER, PRELOADER BACKUP)

• PGPT (Primary-GPT/Main GPT), SGPT (Secondary-GPT/Backup GPT)

• PROTECT1 (PROTECTs), PROTECT2 (PROTECTf)

• NVRAM, NVDATA

• l_fixnv1, l_fixnv2

Although these partitions exist on various Android devices, each vendor has a different implementation and role for them. An outline of these partitions and their importance is provided in this article.

A/B Partition System: Seamless Updates

One of the most common and well-documented partitioning structures in modern Android devices is the A/B partition system. Introduced by Google to enhance OTA (Over-The-Air) updates, this mechanism allows system updates to be installed in the background without disrupting the user experience.

How A/B Partitioning Works

• The system has two copies of key partitions, labeled A and B (e.g., SYSTEM_A and SYSTEM_B).

• When an update is available, the system writes the new update to the inactive partition.

• The device boots from the active partition, while the inactive partition is updated.

• A flag called slot_successful (visible in FASTBOOT data) determines which partition is in use.

• If an update fails, the device can fall back to the previous partition, reducing the risk of a bricked device.

Benefits of A/B Partitioning

• Reduces downtime during updates

• Provides a fail-safe mechanism in case of update failures

• Improves security by ensuring a working backup of the system

This system was introduced with Android 7 (Nougat) in 2016, enhanced further with Android 12, and is expected to improve with Android 15 to optimize storage and free up more space for users.

Understanding Reserved and Secondary Partitions

In additional to the A/B system, Android devices have several secondary and reserved partitions that are all important for data storage, device recovery, and system integrity. An outline of a few important ones is provided below:

NVRAM & NVDATA

• NVRAM (Non-Volatile Random-Access Memory) stores essential network-related configurations, such as IMEI, Wi-Fi MAC address, and Bluetooth addresses.

• NVDATA works alongside NVRAM to maintain these settings dynamically.

• If corrupted, the device may lose network connectivity and require manual restoration.

Fixnv1 & Fixnv2

• These partitions store backup copies of NVRAM data.

• During a firmware flash or format operation, they help recover lost network configurations.

• One partition acts as a temporary storage, while the other is permanent storage.

PGPT & SGPT (Primary and Secondary GPT)

• PGPT (Primary GPT) is the primary partition table that helps the device recognize and manage partitions.

• SGPT (Secondary GPT) is a backup in case the primary table is damaged.

• Essential for partition management and device recovery.

PROTECT1 & PROTECT2

• These partitions store security-sensitive data such as factory settings, calibration data, and DRM keys.

• If erased or corrupted, certain device functionalities (like a secure boot) may be affected.