I've known that the iPhone runs OS X for years now but now all of the sudden it runs iOS 4. Why the change in name? Was there any sudden difference between OS X and iOS 4 to merit it?
iOS is an operating system for mobile devices, first announced for iPhone in 2007. OS X is much older (2001) and developed for Apple computers, now it is called macOS in most cases, but it is not the same as iOS, iPadOS, watchOS, tvOS.
macOS9.2 was a true licensed Unix = Apple had to pay for each Unix license. OSX 10.0 is based on NeXT OS --> based on FreeBSD --> based on BSD --> based on Unix 4. BSD OS was a side-by-side code rewrite open source compatible version, different code, same functionality = No license payment to AT&T, sold its rights to Novell in 1990s, which then sold its Unix business to the Santa Cruz Operation (SCO) in 1995. iOS is a portable version designed for Apple custom RISC architecture based on ARMv7 v8 CPUs, used in iPhones and iPads, = No license payments to ARM. iPad4 Retina was the latest with a custom 32-Bit CPU, does Not have custom 64-Bit RISC instructions = cannot be upgraded to 64-Bit iOS. Microsoft had a similar Windows8 Phone version for ARM CPUs used on some Nokia Cellphones. OSX 10.0 to OSX 10.5 was designed for PowerPC CPUs G3, G4, G5 made by Apple-Ibm-Motolora "AIM" joint venture, IBM continued to develop PowerPC CPUs v9 and v10 used in some servers and high security open source workstations like Raptor Talos ii. OSX 10.6. SnowLeopard to OSX 10.14. Mojave was designed for Intel Macs x86_64 CISC architecture, OSX 10.15.7 Catalina was designed 100% 64-Bit, 32-Bit discontinued, OSX 11 BigSur is designed for Newer Apple Silicon M1 CPUs 64-Bit Only, that are an 8-core version of the 6-core A CPUs used in top of the line latest gen iPhones and iPads. ive read soemwhere that M1 BigSur can install iPhone and iPad Apps in the M1 with the Apple Store. it seems iOS and BigSur have Merged to a single OS, same CPU architecture, but different names because different applications, but same internal structure. in older iOS you could install lightning to USB female adapter, and that to a powered USB Hub, and that to an Apple USB Ethernet adapter, and use an iPad or iPhone with wired Ethernet... Apple was planning the crossover long ago. you can read more details in Wikipedia...
Nice summary. I'm still on Catalina (early 2013 Retina MBP - until it dies) and can run iOS/iPadOS apps on it. Kinda clunky, but it will work.
