When iPhone 4S and Siri were presented, Apple stated that the new assistant will only be available on the latest version of the iPhone terminal and things do not seem to change in the near future. Even so, Siri was one of the main reasons why many users bought the iPhone 4S, but it was also one of the reasons why hackers struggle to port it to old devices. If Siri is so interesting, why doesn't Apple offer it as a paid upgrade to its customers? Well, because an Apple iPhone 4S has implemented a technology called EarSmart which was developed by the company Audience and which does not exist in any other iDevice.
In the iPhone 4, Apple implemented the Audience technology for the first time to reduce background noise and everything works through a chip included in the base plate of the iPhone 4. Because Apple wanted to reduce production costs and free up space chose to implement background noise reduction technology directly in the A5 chip processor, but that's not all because Audience has significantly improved its technology. In the iPhone 4S, we have EarSmart technology that not only reduces background noise when talking on the phone with the device to the ear, but also reduces background noise in a much larger radius around the device so that Siri can be used even while holding the terminal in hand and without being interrupted by the noises around us.
Even after accounting for the dual Cortex-A9 CPUs and the large GPU that provides the A5 with industry-leading 3D graphics performance, the remaining die area seems too large for the usual mundane housekeeping logic. To reduce system cost and eliminate the extra package required for the Audience chip, Apple cut a deal to integrate the noise-reduction technology directly into its A5 processor, which appears in the iPhone 4S. This situation helps explain why Apple does not offer Siri as a software upgrade on the iPhone 4. Although the older phone includes an Audience chip, the company has since improved its technology to handle 'far-field speech.
Since the iPhone 4 doesn't have the same background noise cancellation technology, it's clear that Apple has no serious reason to release a version of Siri that probably won't please every user. Even if for many the reason is far too insignificant, for a company like Apple it represents a solid explanation for offering Siri only for the iPhone 4S.
