Why Siri should (and probably will) come to iPad 2
Since the iPhone 4S features the same A5 processor as the iPad 2, owners of Apple's current-gen tablet have wondered if it's possible that Siri, Apple's new voice assistant, might be offered on the iPad 2. While my colleague Erica Sadun's answer to that is "Don't hold your breath," I only agree with her up to a point: I don't think there are any technical hurdles whatsoever to running Siri on an iPad 2, and the fact that the device doesn't currently feature voice controls is meaningless. I think Siri will come to the iPad 2 eventually -- certainly not right away, but possibly within the next six months.
Voice Control as it now exists on the iPhone 3GS and iPhone 4 doesn't function on the iPad or iPad 2, but there's a reason for that: the existing commands would be essentially useless on those devices. The pre-Siri version of Voice Control allows you to use voice commands to control music playback, dial phone numbers or initiate FaceTime calls, and ask the device for information about the current time or currently playing song. That's about all Voice Control does. Those functions are all useful features on a device that spends much of its time in your pocket, but on an iPad they make very little sense.
On the other hand, Siri's commands would be immensely useful on the iPad. The same things Apple showed off at the "Let's talk iPhone" event, like setting up Reminders and Calendar events or looking up information on Wikipedia or Wolfram Alpha, would be very handy to have -- so handy that I don't see why Apple wouldn't offer them. Apple has long been a company that designs products its own workers want to use, and it's hard to imagine that no one in Cupertino has thought about how Siri could vastly expand the power and capability of the iPad 2.
Since the iPad 2 has both a microphone and the same A5 as the iPhone 4S, there shouldn't be any technical reason why Siri wouldn't function well on that device. Some have speculated that the iPhone 4S has 1 GB of RAM to the iPad 2's 512 MB (a claim that will have to wait for an iFixit teardown before it can be proven or disproven), but my TUAW colleagues don't believe that Siri's functions should be so RAM-intensive that they require such massive amounts of memory.
In fact, we've done some digging into Siri and found that most of the actual work of understanding voice commands gets offloaded to external servers. In essence, the iPhone 4S and its built-in processing functions determine what you said, while Apple's servers translate that into what you meant and send that information back to your iPhone. The pre-processing that takes place on the device itself may be too taxing for an A4 processor, but the iPad 2's A5 should theoretically be able to handle it just fine. Perhaps even better -- Apple has a habit of underclocking CPUs for the iPhone in the interest of power management, so the iPad 2's A5 is likely to outperform that of the iPhone 4S for many functions.
The fact that Apple hasn't yet said one way or another whether Siri will come to devices other than the iPhone 4S also doesn't mean much. The iPhone 4, 3GS, and newer iPod touch models had an exclusive on multitasking for almost exactly six months before iOS 4.2 debuted and brought that feature to the iPad, and the same thing may end up being true for Siri.
Here's what I think is the most likely scenario: Siri will remain an iPhone 4S exclusive at least until the third tier of international rollouts completes in December. In fact, Apple will probably wait until after the end of the holiday quarter and bring Siri to the iPad 2 in the first quarter of 2012. Not only will this give market incentive for people to buy the iPhone 4S by having Siri as a device-exclusive feature during the holiday period, it'll also give Apple's servers and Siri's algorithms time to adjust and scale to the number of inquiries it'll receive.
Once Siri's beta period ends and international rollouts for the iPhone 4S are reasonably complete, that's the perfect time to bring Siri to the iPad 2 in a dot-update to iOS 5. By that time Siri and its supporting infrastructure will be more mature and able to handle the extra load of adding support for one more device type, and it should also help alleviate the typical post-holiday quarter sales slump.
As for the other devices in Apple's iOS stable, like the iPod touch, iPhone 4, and iPhone 3GS, I don't expect them to ever see support for Siri. Siri's developers have already confirmed that many compromises were required to get the service running on the iPhone 3GS, and it's probably the same story for iOS devices with an A4 processor. The 2012 model iPod touch will likely be updated to an A5 processor, however, so we might see Siri support for next year's iPod touch.
For the time being, Siri remains an iPhone 4S exclusive and one we have yet to test for ourselves. We look forward to putting this innovative feature under our interrogation lights once the iPhone 4S is released on October 14.