The iPhone 5s has a burst mode where it takes 10 photos per second. According to this review:
Even HDR shooting doesn’t slow things down much, and there’s no waiting for the phone to digest a long burst either.
Since the iPhone takes multiple exposures to make a HDR photo, how can it do that without slowing down the burst speed? In other words, if the phone can actually take 20 or 30 exposures per second in HDR mode, why doesn't Apple let us take photos at this speed without HDR?
A comment on the aforementioned page says that:
It's just that the two frames are captured in a very rapid succession - I think during the photodiodes' filling with photons.
What does this mean, and how is it different from how cameras normally take photos? Does it mean that the iPhone is taking a burst without closing the shutter (physical or electronic) in between the two photos? If so, won't the data from the first image show up in the second image, defeating the point of taking two photos?
Footnote: If you are wondering that the iPhone does single-photo HDR, it doesn't. You can see the artefacts to the right of the poles in this HDR photo, while the normal version of the photo does not suffer from this problem.