[snvzz]

Most CISC proponents (armchair digital architects) entirely miss the point.

An ISA is the interface between hardware and software. Thus a complex ISA does impose complexity upon both the hardware and the software.

Complexity is inherently (very) bad, and thus needs strong justification.

RISC embodies this idea by recognizing the value of simplicity and requiring any ISA addition be weighted against its complexity cost.

Implementations of RISC philosophy ISAs demonstrate (by achieving or even surpassing parity) the complexity in x86 is not justified, and this is why there hasn't been any tabula rasa CISC architecture worth noting in several decades.

[StressedDev]

I am going to be blunt. If CISC is so bad, why did almost all of the RISC chips from the 1980s and 1990s fail? Why aren't we using them today? The closest you will get is ARM chips. If you are going to claim RISC is fundamentally better, why aren't the fastest and most power efficient chips RISC chips? Why are Amazon, Google, and Microsoft buying an enormous number of x64 chips? It's not because they love the architecture. It's because x64 chips are the best in terms of cost, power usage, and performance.

My guess is the most important thing for chip performance is the manufacturing process. After that, it's things like pipelining, branch predictors, super-scaler design, etc. (I am not an expert and this is just a guess). I don't think instruction set really matters that much when chips have billions of transistors.

RISC was a great idea in the 1970s because a more complex instruction set meant fewer transistors for performance improvements. The same was also true in the 1980s. By 1995-1996, the Pentium Pro was the fastest 32-bit chip. At this point, RISC's proponents had to start explaining why a better instruction set did not translate into a faster chip. They never did. Instead, they keep on banging on the "RISC is better" drum without supplying better chips.

[acdha]

One thing to remember is that chips are complex and defy simple binary classification. Even Intel thought that CISC was on the way out, although they were going down a somewhat extreme path with EPIC, but the most successful approach turned out to be a hybrid where complex CISC instructions were broken into RISC-like micro-ops. That got Intel back in the game with the Pentium Pro getting close enough to the DEC Alpha’s performance lead and with the advantage of not having to recompile everything in an era where that was orders of magnitude harder than it is now. I wouldn’t say either side won since that has been going back and forth for decades now.

It’s also hard to separate that from other factors: was the Pentium more successful than the PowerPC because of CISC or because Intel had much better fabs than Motorola? If Motorola, IBM, DEC, or HP had had less incompetent management at the time it’s possible that we might remember this period very differently.

[snvzz]

>Even Intel thought that CISC was on the way out, although they were going down a somewhat extreme path with EPIC, but the most successful approach turned out to be a hybrid where complex CISC instructions were broken into RISC-like micro-ops.

Note that neither are these micro-ops RISC (they are long, complex and specific to the chip, actually much closer to EPIC), nor was this micro-ops approach new.

Intel tried to use the 64 bit transition to finally abandon x86.

It almost managed to do this, but AMD saw a chance and AMD64 happened, ironically leveraging the x86 software moat against Intel. Software would not migrate to Itanium, but smoothly transition to AMD64.

Without the moat, Itanium was doomed. But it was doomed either way, as was found later, due to its complexity. Complicating compilers, having learned nothing from the RISC paper.

[acdha]

> Note that neither are these micro-ops RISC (they are long, complex and specific to the chip, actually much closer to EPIC), nor was this micro-ops approach new.

I was mostly thinking about them as simpler - which is not the same as simple - but mostly in the larger context of it not being a religion where chip designers pick a side and never budge, when in reality everyone finds ways to use good ideas that make sense for their designs.

[snvzz]

>mostly in the larger context of it not being a religion where chip designers pick a side and never budge, when in reality everyone finds ways to use good ideas that make sense for their designs.

Chip designers design chips (I suspect you meant to emphasize microarchitectures), whereas ISA designers design ISAs.

An ISA designer's concern is to design a good ISA[0]. A good ISA will be chosen and loved by microarchitecture designers. This enthusiasm might then come off as religion-like.

0. https://news.ycombinator.com/item?id=39848530

[snvzz]

>why did almost all of the RISC chips from the 1980s and 1990s fail?

Citation needed.

>Why aren't we using them today?

Because we are using better chips made recently, not the ones from the 80s and 90s.

>Why are Amazon, Google, and Microsoft buying an enormous number of x64 chips?

Because performance vs cost in the current market, as well as access to x86 software moat.

But this is changing. Notably, Amazon has Graviton, Microsoft was Windows for ARM with grease for x86 software, and Google has a digital design team, which is already iterating RISC-V based accelerators.

Facebook, FAANG you have not mentioned, has its own RISC-V server effort.

>I don't think instruction set really matters that much

And yet, you're writing this very opinionated comment about ISAs.

>RISC was a great idea

Yes, it was. This is why the industry did never again make a tabula rasa CISC ISA.

>At this point, RISC's proponents had to start explaining why a better instruction set did not translate into a faster chip.

The RISC chips actually were faster. But this did not matter, as Intel had the better fabs, and the cash.

So Intel was able bruteforce its way into enough performance for cheap enough that the market would then not bother going through the pain of switching ISAs.

>without supplying better chips.

The chips were better despite Intel's fab advantage. But they were not cheaper, nor did it run the software the market wanted to run.

They sure sold these Pentiums, and were able to buy (and kill) Alpha later.

The one and only reason x86 survives to date is this software moat.

This moat advantage is in danger now, thanks to Microsoft's efforts to detach Windows from x86 and provide emulation to handle the transition like Apple did.

[StressedDev]

You asked for a citation about why almost all RISC chips from the 80s and 90s failed. Well, here it is:

- ARM (ARM) - ARM has done very well. It traditionally focused on low power chips. Over the past two decades, ARM has created faster and faster chips. Its chips can now be used in laptop, desktop, and server systems. I would argue ARM is a success. I would also argue it's not clear that ARM systems are faster than Intel or AMD systems.

- Alpha (Digital Equipment / Compaq / Hewlett Packard) - Alpha is dead. No one makes or sells Alpha computers any more.

- MIPS / Silicon Graphics - Silicon Graphics is gone. MIPS may survive as an embedded chip. MIPS chips are not used in used in main stream servers nor do they out preform x86 chips from AMD or Intel.

- PA RISC (Hewlett Packard) - HP dropped this in favor of Intel's Itanium chips.

- POWER (IBM) - This architecture is still being sold by IBM in real products. My guess is it is a good chip but it is still more expensive and slower than chips from AMD and Intel. Still, IBM deserves a lot of credit for keeping POWER going for over 30 years and for outlasting all of the other server/workstation RISC chips from the 1980s and early 1990s (ARM was not in servers or workstations during this time period). One sign that POWER is slower than Intel and AMD is there are no POWER chip benchmark results for the integer speed tests on the SPEC web site (https://www.spec.org/cpu2017/results/cint2017.html). This implies that IBM's cores are slower than x86 cores.

- PowerPC (Motorola and IBM) - This may survive as an embedded chip. It is not used in servers or desktop/laptop computers. Apple was the only user and they switched to Intel in the 2000s (they also recently switched from Intel to their own custom ARM Mx chips).

- SPARC (Sun Microsystems) - The microprocessor design team radically downsized sometime in the last decade (https://www.networkworld.com/article/964265/the-sun-sets-on-...). It still has support but my guess is the chips are not fast or cheap. The only reason you would use it is if you had software you could not move to x86 or ARM systems.

We had 7 RISC chip architectures launch in 1980s and 1990s. 6 were used in workstations and servers. One (ARM) was primary used in low power systems in the 1990s. In 2024, 2 are still going (ARM and POWER), 1 is on life support (SPARC), 2 may be used in some embedded systems (MIPS and POWER PC), and 2 are dead (Alpha and PA RISC).

ARM chips may be able to outperform x86 chips but I have seen very little evidence of this (Apple's M1, M2, and M3 may be better but it is hard to tell without reliable independent benchmarks). POWER is probably a good chip but it has failed to beat x86's performance. The rest are irrelevant in the laptop, desktop, and server world.

My main point is RISC's proponents promised that RISC chips would be faster than CISC chips like the x86/x64 chips. In 2024, we have not seen any evidence that the fastest chip must be a RISC chip. In fact, we have seen the opposite where none of the RISC architecture's hold the undisputed performance crown. If RISC was better, at least one of the RISC chip designs would have defeated AMD/Intel by now.

[snvzz]

>ARM success

Yes.

>Alpha (Digital Equipment / Compaq / Hewlett Packard) - Alpha is dead. No one makes or sells Alpha computers any more.

Important to mention: Intel bought the Alpha IP, thus ensuring Alpha is no longer a problem to them.

>MIPS chips are not used in used in main stream servers nor do they out preform x86 chips from AMD or Intel.

Important to mention: MIPS abandoned MIPS ISA in favor of RISC-V, which doesn't hold the workstation/server performance crown... yet. Anytime now.

>POWER (IBM) - This architecture is still being sold by IBM in real products. My guess is it is a good chip but it is still more expensive and slower than chips from AMD and Intel.

Emphasis on expensive. They would be competitive, except price means they are not.

>SPARC

Register Window was a bad idea after all. Also, Oracle. Might as well be dead.

>We had 7 RISC chip architectures launch in 1980s and 1990s.

In the list, yes. There's more. But it is important to observe that's because the industry stopped launching CISC ones.

And from the CISC ones, only x86 remains.

>My main point is RISC's proponents promised that RISC chips would be faster than CISC chips

There is no such promise in RISC whitepaper. Citation needed as to where this promise is found (and who these RISC proponents are).

>If RISC was better, at least one of the RISC chip designs would have defeated AMD/Intel by now.

No, it does not follow. Furthermore, AMD and Intel can and have made RISC chips before, and will likely make RISC chips again.

A far better question is "has RISC succeeded?", and here the answer is yes. For decades, there have been no tabula rasa CISC ISAs, and among the remaining ones only x86 has some life to it.

Meanwhile, RISC ISAs drive smartphones, the computers that most people use the most, as well as Mac computers, the most prominent alternative to Windows computers in the market.