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When Apple announced their move from the Intel to the ARM processor architecture, it was clearly big news. But it also left many folks with a pretty basic question: What’s the actual difference between the two? At a hardware level, Intel chips are built on the x86 architecture, whereas Arm’s processors use their own, proprietary ARM architecture. In computer science terms, x86 is what’s known as a Complex Instruction Set Computer (CISC) architecture, and ARM is a Reduced Instruction Set Computer (RISC) architecture. There are several differences between the two architectures, but perhaps the most basic one is the way in which they give instructions to the CPU. CISC architectures allow for more complex, “multi-step” instructions, while RISC architectures break instructions down into their individual steps and pass them to the CPU one-by-one. In terms of how the two differ for actual human beings, RISC architectures tend to be extremely energy-efficient, which makes them a great fit for low-power environments like mobile devices and embedded systems. CISC architectures allow developers to tell the CPU what to do using fewer lines of code, which produces more compact programs and makes them appear a bit more “programmer-friendly” in the eyes of some people. In terms of what the changeover will mean for actual Mac app developers, it’s still a little too soon to tell, but Apple is already saying that they’ll provide a range of tools intended to make the transition as smooth as possible, including functionality to automatically translate code written for x86 into something that will work on an ARM architecture, and extensive documentation to help developers port their apps to an ARM version. There has been a great deal of discussion as to why, exactly, Apple decided to make this change — and there are likely several factors behind the decision. For one thing, there have been rumors that Apple wasn’t happy about quality control issues at Intel in recent years. A CNBC report published last week lends some credence to this speculation: It seems that Intel will be forced to delay the release of one of their new chips for half a year due to production issues. In addition, the move is pretty “on brand” for Apple as a company. Cupertino likes to do things in-house whenever it can — and prefers not to be constrained by another company’s quality issues, product offerings, or timetables. One past example of this comes from Apple’s 2008 acquisition of low-power chip manufacturer P.A. Semi (a move which marked the company’s first foray into manufacturing their own ARM chips). At the time, it was reported that the decision had to do with Apple’s dissatisfaction with Intel’s Atom line of chips for handheld devices, which they viewed as insufficiently power-efficient to meet their mobile development needs. In terms of the actual timing of the decision, it’s probably the case that Apple just feels ready to make the leap. They’ve been manufacturing chips for the iPhone and iPad for around 10 years (using the ARM architecture), and they now have a mature, successful silicon engineering division. For this reason, the company is confident that it can do at least as good a job of building processors for the Mac as Intel can. Building a better Mac There are some obvious business reasons for Apple to switch from Intel to ARM processors, but what will the change mean for end users? Will “Apple Silicon” really result in a noticeable improvement to the Mac? Apple seems to think so. They’ve highlighted two key changes that ARM processors will allow them to implement — and say that these will help them to build a faster, more efficient Mac. The first new feature is something called Asymmetric multiprocessing (AMP). AMP means that new Apple Silicon CPUs will have a mix of high-performance cores and power-efficient cores. Intel CPUs are multicore, of course, but all of the cores have relatively similar performance specs. This means that no matter what an app needs to do — whether it’s something that demands maximum performance or just a simple task that isn’t very resource-intensive — all of the processing is being done on a core that’s more or less the same as the others. AMP means that apps will be able to get their computational work done on a core that’s optimized for the kind of task they’re trying to accomplish: Tasks that require max performance will be sent to a high-performance core, and tasks that don’t require much in the way of system resources will be sent to a power-efficient core. The end result will be a Mac that gets all of its work done optimally, which should result in a faster, more efficient machine. The second big change has to do with the way that the CPU and the GPU will share resources. At the moment, Intel Macs often have a CPU and a discrete GPU to handle graphics — and each has its own memory. This leads to computational overhead, since the CPU can only access graphical resources stored in the GPU’s memory by first requesting them and copying them over into its own memory area. Apple Silicon Macs will combine the CPU and GPU into a single system on a chip (SoC), which means that they’ll be working over the same memory. If the CPU needs a graphical resource like an image or a texture, it can get it from its own memory, without any extra steps. As with AMP, the end result for the user will be a Mac that doesn’t need to expend unnecessary effort to get its work done, which should result in increased efficiency and performance.