@Brenda - Re: A bit harsh
Actually, ARM is quite good at 64-bit transparency: 32-bit code doesn't appear to have a penalty, but it is hard to tell when all you can do is compare first-attempt (okay, second-attempt, but Apple's is the first in a client) implementations of ARMv8 with mature, optimised ARMv7 implementations.
That said, I completely agree with you that 64-bit isn't a big performance deal. I've written a lot of code over the last 25 years, for a lot of very varied application areas, and my gut feeling is that outside of scientific modelling, integer maths accounts for the bulk of most applications' calculations (remember that GPUs handle the floating-point for 3D transformations). Of that, I'd guess that 99% can be be accommodated by 32 bit registers. The big performance benefit of 64-bit, that of being able to access more than 4 Gbyte of address space, isn't a whole lot of use on a device with such constrained resources as a tablet. (To be clear, I still think 64 bit is of incredible benefit on desktops and servers, but they have more memory, more storage, and run applications that work with bigger datasets than a tablet.)
Basically, being 64-bit isn't why ARMv8 chips like the A7 are better than their predecessors, but I suppose it's the easiest "this number is bigger" feature for a marketing department to work with, and in the inevitable absence of market-changing new features to trumpet at every iteration, Apple have now joined the tech industry numbers game instead: lighter - nice, more pixels - okay, but... twice as much "bit" as the competition?? Only the first two provide a customer benefit. As a customer, why should I care how wide the ALUs are? it doesn't add anything that will benefit me now, or in the lifetime of the device. It's a willy-waver feature; a bigger number buyers can use when someone challenges your choice of product.
Nor does it mean the device will be faster or better than the competition. Right now, I think a good ARMv7 implementation can still beat an ARMv8 chip, simply because v8 is new, and the vendors are still getting to grips with it. But as the same optimisation is applied to the newer architecture by vendors, we'll see v8 pull ahead.
But again, that performance gain will still have very little to do with it having 64-bit addressing. Not on a tablet, running tablet applications.