Sources from Taiwan's supply chain say Apple will upgrade iphone6s and iphone6s plus RAM to 2GB and use the latest LPDDR4 low-power memory technology. The current IPhone6 and IPhone6 Plus are equipped with only 1GB RAM and are LPDDR3 standard.
In fact, Apple's upgrade of the next iphone's memory is due to this demand, mainly related to the recent exposure of the iOS9 operating system. IOS9 must run on a device running memory up to 1GB to avoid departing from the Apple user base.
So only 512MB running memory iphone4s is very difficult to have the opportunity to upgrade to the iOS9, although there is no exact information about iphone4s upgrade to iOS9, but the possibility should not be small, iphone4s users have the best to change the heart of the machine!
Equipment expected to run IOS9:
ipad 3, ipad 4, ipad Air, ipad Air 2, ipad Air 3*, ipad pro*
ipad Mini 2, ipad Mini 3, ipad mini 4*
iphone 5, iphone 5c, iphone 5s, iphone 6, iphone 6 Plus, iphone 7 series*
ipod Touch 5 (Note: * is not sure)
If you're iphone4s, we can use the IOS9 system. Because IPhone5S is equipped with a strong A7 processor, it runs iOS9 can be very smooth