What does a 64-bit ARM processor mean?

The history of 64-bit computing is quite rich and interesting. Companies such as Cray have started using 64-bit registers in their systems in the 70 's, but the truly pure 64-bit computations didn't really come until the 90 's. The first is the R4000 of MIPS, then the DEC Alpha processor. By the middle of the 90, both Intel and Sun had 64-bit designs. The real turning point for consumers is that AMD released a 64-bit PC processor in 2003 that is compatible with the Intel 32-bit x86 processor.

What does a 64-bit ARM processor mean?

Further forward into the 10, PC sales are falling, with most smartphones and tablets owning a 1-2ghz processor between the main frequencies. But they use a 32-bit architecture, not the 64-bit architecture used by modern PCs and servers. So far, this is acceptable. Smartphones do not go with the PC and the processors need to be energy efficient enough to maximize their endurance.

But with the development of devices and the growing popularity of new technologies-speech recognition, 3D games and high-resolution displays-the ability of 32-bit processors has been pushed to the limit.

　　What does a 64-bit ARM processor mean?

Arm saw the need for 64-bit energy-efficient processors and started the development of new designs as soon as the formal release of the ARMV8-A architecture (the first arm of the 64-bit instruction set), and learned from other chip designers who chose to develop 64-bit technology. ARM's new 64-bit architecture is fully compatible with its 32-bit architecture, which means that if the processor runs on a 64-bit system, it can run unmodified ARMv7 32-bit binaries. For Android, this means that once the kernel is ported to 64 bits (thanks to Linaro, they already are), the rest of the system, from the core library to the application to the game, can be switched between 32-bit or 64-bit.

Last year, Apple shocked the entire mobile world with its all-new 64-bit A7 processor for the iphone 5s. A7 uses the apple-designed ARMV8 dual-core processor, known as Cyclone. It uses two 64KB L1 caches (used by two cores), a 1MB L2 cache (shared by two cores) and a 4MB L3 cache (for the entire SOC). Apple has the ARM architecture authorization, which means it can design its own processor from scratch, but only if the processors must be ARM compliant. ARM has a suite of tests to check if these processors are compatible.

Over the next few months, we will see Qualcomm, MediaTek and Samsung launch their own 64-bit ARM processors. Taking into account Android's 64-bit effort, it won't be long before we see 64-bit devices running on the 64-bit Android system. But what does a 64-bit processor mean for developers and end users?

64-bit architecture that benefits from arm

　　What does a 64-bit ARM processor mean?

The center of each CPU is a set of registers, all of which are internal storage slots for storing numbers and addresses. These slots are reused when performing complex tasks. If all registers are occupied, the only way to handle them is to store one of the registers in memory, use registers for the next task, and then reload the previous values from memory. For humans, it all happened in a flash. But for the processor, this is actually a very time-consuming sequence, not very efficient.

The 32-bit ARMV7 architecture has 15 general-purpose registers, each with 32-bit widths. The ARMV8 architecture has 31 general-purpose registers, each of which is 64-bit wide. This means that the optimized code should use internal registers more frequently than memory, while retaining larger numbers and addresses. As a result, ARM's 64-bit processors can run faster.

In energy efficiency, the use of 64-bit registers does not increase power consumption. In some cases, the 64-bit core performs part of the task faster and, due to the decrease in running time, makes it more energy-efficient than the 32-bit core.

Addressing (addressing) is another layer of 64-bit processors. In the PC and server realms, the 32-bit limitation is primarily on accessible memory. If you want to use more than 4GB of RAM, you need to use a 64-bit processor. Because the large physical Address extension (LPAE) can be used, some ARMV7 processors can use more than 4GB of memory, so strictly speaking, the memory limit is not the problem that the ARM processor encounters. Due to the presence of LPAE, the CORTEX-A15 processor can handle 1024GB of memory, while 64-bit processing capacity is up to 2 million TB. So in a short period of time, no smart phone needs a full 64-bit address. It is meaningless to pursue an address space that will never be used, so the ARMV8 architecture employs 48-bit addressing, which is already 256TB.

While there are no programs or games that use terabytes of memory, on the other hand, this ability to address is important. Modern 3D games usually carry a lot of resources, and when they have more than 4GB of accessible space, these resources can be more easily mapped to memory. In this way, the speed of the game will be improved, and direct access to game multimedia resources become possible.

　　It's not just smartphones and tablets.

The benefits of 64-bit computing on ARM are not limited to smartphones and Tablet PCs. Arm's ecosystems are vast, and their processors are used by many different types of devices. The server market is an area in which arm processors have limited influence. The development of the information age has allowed sustained and rapid growth in the energy consumption of data centres, and any technology that can reduce energy use is a saving for money and natural resources. In addition to saving energy, the use of 64-bit ARM chips in the server has other benefits. These servers will dissipate heat, which means you can focus them together without having to worry about overheating. As a result, the cost of cooling will also be reduced.

As for server software, Linux is already 64-bit operating system, and its mainline kernel has joined the support for ARMV8. This means that it is not difficult to make a server running on 64-bit Linux and ARM processors.

　　Summarize

Thanks to the arm,64-bit mobile computing age, it's coming. These new processors are not only faster, but also open up more possibilities for mobile platforms. From the 32-bit to 64-bit migration path has been paved, no matter what the operating system, developers from 32 to enter 64 without any surprises.

Over the next few months, ARM partners will launch cortex-a53 and CORTEX-A57 processors. Some of them will use a dual-core or quad-core standard configuration, some will choose big. Little configuration. But one thing is for sure, and that is that this is an exciting time for both arm and the average user.