Shulou(Shulou.com)05/31 Report--

­64-bit mobile processors made their debut in 2013, while Apple's iOS was the first mobile operating system to support 64-bit computing. Interestingly, from the recent news, it is possible for Apple to formally abandon support for 32-bit applications in iOS 11 and formally complete the complete transition to the 64-bit ecosystem. In fact, this is the inadvertent revelation of an error message in iOS 10.3 beta. When a user tries to run a 32-bit application, the system tells the user that it cannot be run in a future version, and the developer needs to improve the adaptation.

­Apple has provided similar hints on the iOS platform more than once, and would very much like developers to provide only 64-bit applications. At the end of last year, for example, Apple removed a certain number of apps from App Store on the grounds of incompatibility and sent an email to developers reminding them that application development must be based on 64-bit.

Generally speaking, we don't care much about whether the system or phone is 32-bit or 64-bit. After all, new devices are always compatible with both 32-bit and 64-bit applications. However, given that Apple can always have an impact on Google's mobile ecosystem, it is necessary to discuss why Apple made such a move and whether Android should follow suit.

­32 bit and 64 bit

­first of all, we should briefly understand the background of 32-bit and 64-bit. 32-bit and 64-bit generally refer to the general register bit width of CPU. Compared with 32-bit, the CPU bit width of 64-bit is doubled to enable it to handle more and more accurate data, so it can speed up data processing, especially in the case of load. In popular terms, 32-bit and 64-bit are the difference between four lanes and eight lanes, which are obviously faster during the congested evening rush hour.

­of course, the 64-bit addressable range is greatly expanded, and 32-bit systems support a maximum of 4G memory. In addition, 32-bit systems and 64-bit systems need to be installed to support the corresponding software mode operating system and driver software, that is, 32-bit can only install 32-bit, 64-bit install 64-bit software, but compatible with 32-bit computing.

­back to the topic of ARM processors. During the transformation of ARM from 32-bit ARMv7-A to 32-bit / 64-bit ARMv8-A, a large number of new instructions have been introduced to enhance the functionality, that is, the AArch64 instruction set. However, in order to ensure the backward compatibility of ARMv8, ARM still retains the existing AArch32 and Thumb-32 instruction sets in architecture design. Although this means that the CPU core pipeline part needs to be more designed and takes up more extremely limited chip space, it ensures that these traditional instructions can also work with the new hardware.

­it is important to note that a single application is too long to use both ARMv7 and ARMv8 execution states at the same time, because there is no interaction between AArch64 and the AArch32 and Thumb-32 instruction sets. As a result, applications written directly based on the AArch64 instruction set and ARMv8 processors cannot run on ARMv7 Cortex-A series processors.

­however, applications written on ARMv7 Cortex-A processors can still run on ARMv8 processors, after all, with reserved AArch32 and Thumb-32 execution states.

To put it bluntly, if Apple did that, machines like the iPhone 5, which are based on ARMv7 processors, would not be able to upgrade to the iOS 11 operating system.

­Why does Apple insist on turning to 64-bit

­Apple's abandonment of support for 32-bit applications shows that in the future it will fully embrace the AArch64 execution state, its hardware processor and software iOS system, as well as the design of applications, all of which will only apply to the AArch64 instruction set function. Of course, there are many benefits, including larger addressing range, support for larger memory, simplified assembler, double-precision floating-point and more advanced SIMD operations, and accelerated hardware encryption performance up to 3 to 10 times.

­however, developers and developers will no longer be able to use the AArch32 and Thumb-32 instruction sets because the application must be updated. Of course, in addition to forcing developers to take advantage of the latest features of the new 64-bit architecture, it is also very helpful for Apple to do a better job of designing the next generation of CPU. Apple has an excellent chip design team and has been planning to give up support for the old architecture, so that it can free up as much chip space as possible, reduce manufacturing costs, or use the free space to enhance CPU, GPU and the rest, or introduce more advanced features.

We don't know how Apple will design the next-generation chip, perhaps to further optimize the CPU for 64-bit, not necessarily all to 64-bit, retaining some of the 32-bit instructions required for traditional hardware, without breaking the license agreement with ARM. Because ARM usually requires CPU designs based on its authorized architecture, it is important to support all instruction sets, and if you comply with this rule, Apple's chips also need to retain support for AArch32 and Thumb-32 in order to pass ARM conformance tests. However, ARM itself advocates flexible design. For example, Cortex-A32 is based on the 32-bit version of ARMv8 architecture, and it is not very clear which instruction set is mandatory, which is tantamount to giving Apple more room to play.

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So, should the Android camp follow suit?

­there are pros and cons, and it is not entirely infeasible, and for the same reasons mentioned above, as long as Google and smartphone chip developers, such as Qualcomm and MediaTek, work together on software and hardware. But it is undeniable that the Android ecosystem is much larger than Apple, with a large number of different hardware configurations, and it is believed that it will be difficult to organize quickly if the same change is performed immediately, and may even be interrupted in the process.

Nonetheless, Google could theoretically do something similar in terms of software, forcing all Google Play store apps to move to 64-bit versions. However, it also takes a long time to transition. Although today's entry-level smartphones and tablets are equipped with 64-bit processors, they still rely on a large number of 32-bit applications. And not many of them are perfectly compatible with 64-bit instruction sets, and the consequences of giving up backward compatibility are unimaginable.

­seriously, it doesn't make sense for the Android biosphere to migrate completely to 64-bit. For example, many Android in-car entertainment systems are still built on ARMv7 processors. Smartwatches, including those from Huawei, Sony and LG, all carry 32-bit ARM Cortex-A7 processor designs.

In addition, the chips of Google's recently announced Android Things Internet of things platform are not compatible with 64-bit applications. So there is no way for the Android camp to fully transition to a single 64-bit computing? This is not the case, but it is foreseeable that Android will still provide 32-bit support in the future, which is the best solution for both worlds.

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