4-inch iPhone to sport Apple A9 processor, iPad Air 3 will run the A9X

In a Bloomberg Businessweek article about the secretive chip design labs Apple has in Cupertino, CA and Israel, an interesting tidbit of information about the devices expected to be announced on March 15 slipped out. The article notes that the upcoming 4-inch iPhone will be powered by the A9 SoC (System on a Chip) while the iPad Air 3 is expected to run the A9X.

The A9 is currently used in the flagship iPhone 6s and 6s Plus, while the A9X is found in the iPad Pro. While these SoCs might be considered somewhat overpowered for the devices that they'll be used in, Apple could very well run the chips at a lower clock rate in order to achieve better battery life. 

One feature of the A9 and A9X chips is the built-in M9 motion coprocessor. It's used to capture pace information while running or walking, but also serves as the engine for "Hey Siri" -- the capability of newer devices to use Siri without touching the device -- and powers the barometer that tracks the number of flights of stairs you climb each day. 

What's a bit confusing about the announcement is that given the power of the A9 SoC, the 4-inch iPhone could very well have more power and battery life than the iPhone 6. If pricing comes in below $500 (without subsidy), many buyers could choose to go with the smaller device.

The two new devices are expected to go on sale on Friday, March 18.