Brief Notes
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Benefits of the A7-based, 64-bit architecture introduced with the iPhone 5s

Benefits of the A7-based, 64-bit architecture introduced with the iPhone 5s

Daniel Eran Dilger in Hands-on with the new 64-bit A7-powered iPhone 5s with new M7, camera features & Touch ID:

More recent iPhones have all used the ARMv7 instruction set. For last year’s A6, Apple created a custom “Swift” core using an extended ARMv7 instruction set and based on the ARM Cortex-A9 architecture, incorporating some features of the ARM Cortex-15 architecture designed for server applications.

Since then, Samsung debuted its own chip for the Galaxy S4 using stock ARM Cortex-15 cores, and optimized to shine at benchmarks. Apple took a different tack with its own A7, jumping to the new 64-bit ARMv8 instruction set of the ARM Cortex-A50 series core designs.

The modern instruction set of ARMv8 not only supports running both 32- and 64-bit apps, but also expands the number of both floating point and general purpose registers, uses 64-bit addressing and allows 32-bit instructions to take either 32- or 64-bit arguments. These upgrades are a package deal, and each part of the jump is significant and noteworthy.

Advancing to a 64-bit instruction set essentially means that big math problems can be worked out faster in larger chunks, not just boosting performance but also allowing the processor to finish its work faster and drop back down into a lower power mode, contributing to energy savings even while delivering up to twice the computational performance.

iOS 7 on iPhone 5s gets a native 64-bit kernel, libraries and drivers and Apple has ported all of its own bundled apps to 64-bit, but the device can run both 32- and 64-bit apps without users needing to worry about which they have.

Pundits have already started issuing shill contempt for Apple’s “first to 64-bit” claim, but you can identify those that don’t know what they’re talking about much by how many times they repeat the idea that you need a 4GB boundary before you need a 64-bit processor architecture, while also noting that iOS devices haven’t hit any 4GB frontier (iPhones and iPads have historically maxed out at 1GB of system RAM; iPhone 5s appears to have 2GB).