Why Do We Use x86 CPUs?

bluefoxlucid asks: "With Apple having now switched to x86 CPUs, I've been wondering for a while why we use the x86 architecture at all. The Power architecture was known for its better performance per clock; and still other RISC architectures such as the various ARM models provide very high performance per clock as well as reduced power usage, opening some potential for low-power laptops. Compilers can also deal with optimization in RISC architectures more easily, since the instruction set is smaller and the possible scheduling arrangements are thus reduced greatly. With Just-in-Time compilation, legacy x86 programs could be painlessly run on ARM/PPC by translating them dynamically at run time, similar to how CIL and Java work. So really, what do you all think about our choice of primary CPU architecture? Are x86 and x86_64 a good choice; or should we have shot for PPC64 or a 64-bit ARM solution?" The problem right now is that if we were going to try to "vote with our wallets" for computing architecture, the only vote would be x86. How long do you see Intel maintaining its dominance in the home PC market?

Comments

Easy

[Short Circuit]

Until someone replaces the PC.

PC architecture sits in a local minima where the fastest route to greater profits lies in improving existing designs, rather than developing new approaches.

The reason "We" use x86 is because "we" use PCs, where x86 technology is dominant and obvious. However, "we" also use PDAs, cell phones, TiVos and even game console systems. As the functions of those devices melt into a new class of unified devices, other architectures will advance.

The real irony is that, for most of these other devices, the underlying architecture is invisible. Few know that Palm switched processors a few years back. Fewer still know what kind of cpu powers their cell phone.

Re:Easy

[ergo98]

Windows NT was designed to run on i386, MIPS, PPC and Alpha. Over the years, Microsoft discontinued support for the various platforms

At the time Microsoft was hedging their bets as everyone ranted about the next generation of RISC chips storming the market. Endlessly we'd hear about how the x86 line was dead, and the only improvements would be to move to the next generation (Intel themselves was heavily focusing on RISC as well -- think of the i860).

We never did because those alternatives never delivered on their promise. Ever since 680x0 processors, the highest performance per dollar crown has been held, with only a couple of very short term or niche exceptions, by the x86 line. When given the option of running software on a variety of platforms, customers always ended up buying the x86.

Look at Linux -- so many platforms supported, yet on the desktop and up level, overwhelmingly it's run on x86. This has been the cast over its history.

Why do we ...

[jbeaupre]

Why do we drive on the right side of the road in some places, left in others?
Why do most screws tighten clockwise?
Why do we use a 7 day calender, 60 second minutes, 60 minute hours, and a 24 hour clock like the Sumerians instead of base 10?
Why do we count in base 10 instead of binary, hex, base 12?
Why don't we all switch to Esperanto or some other idealized language?
Or if you're familiar with the story: Why are the Space Shuttle boosters the size they are?

Because sometimes it's easier to stick with a standard.

There. Question answered. Next article please.

Where The Money Is

[spoonboy42]

There's no doubt that x86 is an ugly, hacked-together architecture whose life has been extended far beyond reason by various extensions which were hobbled by having to maintain backwards compatibility. x86 was designed nearly 30 years ago as an entry level processor for the technology of the day. It was originally built as a 16-bit architecture, then extended to 32-bit, and recently 64-bit (compare to PowerPC, designed for 64-bit and, for the earlier models, scaled back to 32-bit with forward-looking design features). Even the major x86 hardware vendors, Intel and AMD, have long since stopped implementing x86 in hardware, choosing instead to design decoders which rapidly translate x86 instructions to the native RISC instruction set used by the cores.

So why the hell do we use x86? A major reason is inertia. The PC is centered around the x86, and there are mountains and mountains of legacy software in use that depend on it. For those of us in the open-source world, it's not to difficult to recompile and maintain a new binary architecture, but for all of the software out there that's only available in binary form, emulation remains the only option. And although binary emulation of x86 is always improving, it remains much slower than native code, even with translation caches. Emulation is, at this point, fine for applications that aren't computationally intensive, but the overhead is such that the clocks-per-instruction and performance-per-watt advantages of better-designed architectures disappears.

A side effect of the enormous inertia behind x86 is that a vast volume of sales goes to Intel and AMD, which in turn funds massive engineering projects to improve x86. All things being equal, the same investment of engineer man-hours would bear more performance fruit on MIPS, SPARC, POWER, ARM, Alpha, or any of a number of other more modern architectures, but because of the huge volumes the x86 manufacturers deal in, they can afford to spend the extra effort improving the x86. Nowadays, x86 has gotten fast enough that there are basically only 2 competing architectures left for general-purpose computing (the embedded space is another matter, though): SPARC and POWER. SPARC, in the form of the Niagra, has a very high-throughput multithreaded processor design great for server work, but it's very lackluster for low-latency and floating-point workloads. POWER has some extremely nice designs powering next-generation consoles (Xenon and the even more impressive Cell), but the Cell in particular is so radically different from a standard processor design that it requires changes in coding practice to really take advantage of it. So, even though the Cell can mop the floor with a Core 2 or an Opteron when fully optimized code is used, it's easier (right now at least) to develop code that uses an x86 well than code which fully utilizes the Cell.