The stock system partition is roughly 1.5GB—far too small for even Android 7.1. A patched download includes a PIT (Partition Information Table) file or an update-script that resizes system , cache , and userdata partitions, often sacrificing the preload partition.
Some patched builds require a separate “patch2.zip” for sensors or GPS. Read the XDA thread carefully.
: A slightly older but often more fluid alternative for the limited 1GB RAM of this device. postmarketOS
: The most popular stable upgrade, often including security patches up to 2018 or later. CyanogenMod 13 (Android 6.0.1 Marshmallow)