iPhone4 ios7.1.2 cannot be downgraded for the following reasons:

1. Apple has now closed the verification for os7.1.2 and below, and downgrading is no longer possible.

2. Each iPhone is independent and unique. Other machine data is not available.

ios system:

iOS is a mobile operating system developed by Apple. Apple first announced this system at the Macworld conference on January 9, 2007. It was originally designed for use with the iPhone, and was later applied to iPod touch, iPad, Apple TV and other products. iOS, like Apple's Mac OS X operating system, is a Unix-like commercial operating system. Originally, this system was called iPhone OS. Because iPad, iPhone, and iPod touch all use iPhone OS, it was announced at the 2010 WWDC conference that it would be renamed iOS (iOS is a registered trademark of the network equipment operating system of the American company Cisco, and Apple's name change has been authorized by Cisco).

ios advantages: low configuration and high performance.

ios Disadvantages: The system is completely closed.