iOS 8 on the iPhone 4S: Performance isn't the (only) problem

New OS wants screen space and processing power that the old phone doesn't have.

iPhone 4S review - The Verge

iOS 9 on the iPhone 4S: A stay of execution, nothing more

Forget the iPhone 5, Apple's next phone is the iPhone '4S

10 Common iPhone 4s Problems & How to Fix Them

iPhone 4S owners file suit against Apple, claim iOS 9 made phones unbearably slow : r/technology

iPhone 4S Review

Question] Got a sealed iPhone 4s 32GB. Came on iOS 6.1.2, I was hoping for 6.0 or something, but at least it isn't iOS 6.1.3. Is this thing rare? : r/LegacyJailbreak

iOS 8 review: the iPhone and iPad get customised, extended and deepened, Apple

iOS: A visual history - The Verge

iOS 9 on the iPhone 4S: A stay of execution, nothing more

Will iOS 9 slow down my iPhone 4s or iPhone 5/5s? Perhaps a little (Video) - 9to5Mac

Read this before upgrading your iPhone 4s to iOS 8

How to speed up iPhone 4

iOS 8.2 iPhone 4s Reviews: Should You Install iOS 8.2?

How to install iOS 15 on an iPhone 4s and an iPhone 5s - Quora