What are the advantages of x86 CPUs over ARM?

Question

Now that Apple is switching the MacOS platform to ARM chips, much has been said about the benefits of ARM processors (they save energy, are passively cooled, and the Apple M1 seems to be faster than even an Intel Core i9 processor).

I'd like to know what advantages of the x86 platform are left. Are there any specific circumstances where the x86 CPUs still have the edge? AFAIK they have an much bigger instruction set than the ARM chips. Under what circumstances is the bigger instruction set an advantage, and why?

Note that I'm not asking about a specific software ecosystem like Windows. I know that Windows has many software titles (e.g. games) that don't run (yet) on any ARM platform. That's not the answer I want to hear. An ecosystem advantage like that of Windows is more or less baggage from previous years. It does not necessarily mean that the CPU platform is in any way better, today.

Answer 1

I'll start with the commonly known stuff, that are currently talked about the most.

x86

All x86 processors are developed from the CISC (Complex Instruction Set Computers) architecture. The x86 processors allow you to perform several activities at the same time from a single instruction. Also, they can perform numerous simultaneous tasks without any of them being affected.

This makes them very sophisticated and advanced processors, allowing many complex calculations in a short time. The disadvantage of this design is that they need a lot of power to function and more power means more heat.

Summary: x86 chips are designed to be power hungry and high clocked, multi-thread, high instructions per cycle. In the general use-case they will be a lot faster than your common ARM chip.

ARM

As for ARM processors, they are based on the RISC (Reduced Instruction Set Computer) architecture, which is much simpler than CISC. These processors can do a much smaller number of calculations since they require several commands to act.

RISC instructions are smaller and faster to process, so in part, the disadvantage of having to process several commands for a single action is minimized. Still, ARM processors are much less powerful than the x86.

Summary: ARM chips are designed for low power draw, flexibility, low cost and low heat with good performance.

source of the info above

SoC M1

M1 is not a CPU. It is a whole system of multiple chips put into one large silicon package. The CPU is just one of these chips. And that's the main reason why it's so different and fast compared to the typical ARM chip.

Basically, the M1 is one whole computer onto a chip. The M1 contains a CPU, graphical processing unit (GPU), memory, input and output controllers, and many more things making up a whole computer. This is what is call a system on a chip (SoC).

In the past computers would have multiple physically separate chips on the motherboard of the computer. However because we are able to put so many transistors on a silicon die today, companies such as Intel and AMD began putting multiple microprocessors onto one chip (CPU cores). One core is basically a full independent chip that can read instructions from memory and perform calculations. This has for a long time been the name of the game in terms of increasing performance - just add more general-purpose CPU cores.

Instead of adding ever more general-purpose CPU cores, Apple has followed another strategy - they have started adding ever more specialized chips doing a few specialized tasks. The benefit of this is that specialized chips tend to be able to perform their tasks significantly faster using much less electric current than a general-purpose CPU core.

Hope that answers your question.

You can find more details on the M1 where I got the info for the second part of the answer. There is a lot of additional and interesting info on the CPU market and the software differences inside the M1 and Intel/AMD chips: link

Answer 2

There are far less advantages in both directions than you might think.

The reason is, that currently there are actually no modern x86 CPUs on the market. Both Intel and AMD don't actually use x86 cores, but instead proprietary RISC cores, with microcode that translates the x86 code to RISC code on the fly at execution time.

ARM chips on the other hand don't use microcode, bun instead directly run their code on an ARM RISC core.

So the cores that do the actual execution are pretty similar. The usage of microcode, though, is the biggest difference. For ARM this is a small advantage for calculation power per watt. But for x86 CPUs that means that the microcode can be updated after production (so with a regular OS update) to fix bugs or improve performance.

The actual performance or power consumption differenced come down to the manufacturers, their priorities and their research. Intel actually made quite decent x86 phone CPUs, but marges were too low for them and the competition had too much of a headstart.

Also, high performance ARM CPUs for desktop and servers are totally possible, but x86 has almost 100% market share there and had that for almost 20 years. That's a very tough market to break into. But it's totally possible, as seen with Apple.

So it has much more to do with money, markets and customers, than with actual advantages of the architectures.

What is the difference between ISAs and implementations?

When talking about ISAs, people often confuse the advantages of specific ISAs with the advantages of specific implementations.

So for example, you will often hear things like "x86 has more performance" or "ARM is more power efficient". These things don't actually have anything to do with the ISA, but are implementation specific.

The ISA is nothing more than the language the CPU speaks. It does not say anything at all about the implementation.

So saying "ARM is more power efficient", because you have seen a few power-efficient ARM CPUs is like saying "People who speak German are blond".

The real difference is that there are two strong mobile ecosystems that mainly use ARM (Android and iOS). You can run Androidx86, but many apps won't work on x86 (Source: me, I had an x86 tablet). So because ARM is used a lot in mobile devices, there will be more funding for mobile ARM CPUs.

And there are very strong x86 ecosystems for desktop and server, so there is more research into high performance x86 chips.

Counterexamples

The Intel Atom x6200FE has a TDP of 4.5W. That's less than half of the Snapdragon 888, which has a TDP of 10W.

The Ampere Altra Max is a 128 Core Server ARM CPU, with a TDP of 250W. This thing strips the socks off most x86 CPUs on the market, in terms of performance.