Skip to content(if available)orjump to list(if available)

100x defect tolerance: How we solved the yield problem

ChuckMcM

I think this is an important step, but it skips over that 'fault tolerant routing architecture' means you're spending die space on routes vs transistors. This is exactly analogous to using bits in your storage for error correcting vs storing data.

That said, I think they do a great job of exploiting this technique to create a "larger"[1] chip. And like storage it benefits from every core is the same and you don't need to get to every core directly (pin limiting).

In the early 2000's I was looking at a wafer scale startup that had the same idea but they were applying it to an FPGA architecture rather than a set of tensor units for LLMs. Nearly the exact same pitch, "we don't have to have all of our GLUs[2] work because the built in routing only uses the ones that are qualified." Xilinx was still aggressively suing people who put SERDES ports on FPGAs so they were pin limited overall but the idea is sound.

While I continue to believe that many people are going to collectively lose trillions of dollars ultimately pursuing "AI" at this stage. I appreciate the the amount of money people are willing to put at risk here allow for folks to try these "out of the box" kinds of ideas.

[1] It is physically more cores on a single die but the overall system is likely smaller, given the integration here.

[2] "Generic Logic Unit" which was kind of an extended LUT with some block RAM and register support.

dogcomplex

Of course many people are going to collectively lose trillions, AI's a very highly hyped industry with people racing into it without an intellectual edge and any temporary achievement by any one company will be quickly replicated and undercut by another using the same tools. Economic success of the individuals swarming on a new technology is not a guarantee whatsoever, nor is it an indicator of the impact of the technology.

Just like the dotcom bubble, AI is gonna hit, make a few companies stinking rich, and make the vast majority (of both AI-chasing and legacy) companies bankrupt. And it's gonna rewire the way everything else operates too.

idiotsecant

>it's gonna rewire the way everything else operates too.

This is the part that I think a lot of very tech literate people don't seem to get. I see people all the time essentially saying 'AI is just autocomplete' or pointing out that some vaporware ai company is a scam so surely everyone is.

A lot of it is scams and flash in the pan. But a few of them are going to transform our lives in ways we probably don't even anticipate yet, for good and bad.

Retric

I’m not so sure it’s going to even do that much. People are currently happy to use LLM’s, but the outputs aren’t accurate and don’t seem to be improving quickly.

A YouTuber watch regularly includes questions they asked Chat GPT and very single time there’s a detailed response in the comments showing how the output is wildly wrong from multiple mistakes.

I suspect the backlash from disgruntled users is going to hit the industry hard and these models are still extremely expensive to keep updated.

ithkuil

Dollars are not lost; they are just very indirectly invested into gpu makers (and energy providers)

girvo

> Xilinx was still aggressively suing people who put SERDES ports on FPGAs

This so isn't important to your overall point, but where would I begin to look into this? Sounds fascinating!

ChuckMcM

Well this was the patent they were threatening with as I recall (https://patents.google.com/patent/US20030023912A1/en) and there was this one too: https://patents.google.com/patent/US5576554A/en

Basically the "secret sauce" of the startup recruiting me was that they were going to do wafer scale FPGAs that could be tiled together to build arbitrarily complex systems like military phased array radars and such. All very hush hush but apparently they had recruited some key talent from Xilinx which was annoying Xilinx.

nroize

Not OP but I was curious too. Here's all I could find that seemed related: https://www.businesswire.com/news/home/20200121005582/en/Xil...

enragedcacti

Any thoughts on why they are disabling so many cores in their current product? I did some quick noodling based on the 46/970000 number and the only way I ended up close to 900,000 was by assuming that an entire row or column would be disabled if any core within it was faulty. But doing that gave me a ~6% yield as most trials had active core counts in the high 800,000s

ChuckMcM

I could guess that it helps with heat dissipation/management. But I don't know. That guess is from looking at the list of patents[1] they have.

[1] https://patents.justia.com/assignee/cerebras-systems-inc

projektfu

They did mention that they stash extra cores to enable the re-routing. Those extra cores are presumably unused when not routed in.

enragedcacti

That was my first thought but based on the rerouting graphic it seems like the extra cores would be one or two rows and columns around the border which would only account for ~4000 cores.

__Joker

"While I continue to believe that many people are going to collectively lose trillions of dollars ultimately pursuing "AI" at this stage"

Can you please explain more why you think so ?

Thank you.

mschuster91

It's a hype cycle with many of the hypers and deciders having zero idea about what AI actually is and how it works. ChatGPT, while amazing, is at its core a token predictor, it cannot ever get to an AGI level that you'd assume to be competitive to a human, even most animals.

And just as every other hype cycle, this one will crash down hard. The crypto crashes were bad enough but at least gamers got some very cheap GPUs out of all the failed crypto farms back then, but this time so much more money, particularly institutional money, is flowing around AI that we're looking at a repeat of Lehman's once people wake up and realize they've been scammed.

dsign

Those glorified token predictors are the missing piece in the puzzle of general intelligence. There is a long way to go still in putting all those pieces together, but I don't think any of the steps left are in the same order of "we need a miracle breakthrough".

That said, I believe that this is going one of two ways: we use AI to make things materially harder for humans, in a scale from "you don't get this job" to "oops, this is Skynet", with many unpleasant stops in the middle. By the amount of money going into AI right now and most of the applications I'm seeing being hyped, I don't think we have have any scruples with this direction.

The other way this can go, and Cerebras is a good example, is that we increase our compute capability and our AI-usefulness to a point where we can fight cancer and stop/revert aging, both being a computational problem at this point. Even if most people don't realize it, or most people have strong moral objections to this outcome and don't even want to talk about it, so it probably won't happen.

In simpler words, I think we want to use AI to commit species suicide :-)

KronisLV

> And just as every other hype cycle, this one will crash down hard.

Isn't that an inherent problem with pretty much everything nowadays: crypto, blockchain, AI, even the likes of serverless and Kubernetes, or cloud and microservices in general.

There's always some hype cycle where the people who are early benefit and a lot of people chasing the hype later lose when the reality of the actual limitations and the real non-inflated utility of each technology hits. And then, a while later, it all settles down.

I don't think the current "AI" is special in any way, it's just that everyone tries to get rich (or benefit in other ways, as in the microservices example, where you still very much had a hype cycle) quick without caring about the actual details.

idiotsecant

All the big LLMs are no longer just token predictors. They are beginning to incorporate memory, chain of thought, and other architectural tricks that use the token predictor in novel ways to produce some startlingly useful output.

It's certainly the case that an LLM alone cannot achieve AGI. As a component of a larger system though? That remains to be seen. Maybe all we need to do is duct tape a limbic system and memory onto an LLM and the result is something sort of like an AGI.

It's a little bit like saying that a ball bearing can't possibly ever be an internal combustion engine. While true, it's sidestepping the point a little bit.

Shorel

While I basically agree with everything you say, I have to add some caveats:

ChatGPT, while being as far from true AGI as the Elisa chatbot written in Lisp, is extraordinarily more useful, and being used for many things that previously required humans to write the bullshit, like lobbying and propaganda.

And Crypto... right now BTC is at an historical highest. It could even go higher. And it will eventually crash again. It's the nature of that beast.

immibis

Why do you think that an AGI can't be a token predictor?

CamperBob2

it cannot ever get to an AGI level that you'd assume to be competitive to a human, even most animals.

Suppose you turn out to be wrong. What would convince you?

ChuckMcM

I would guess you're not asking a serious question here but if you were feel free to contact me, it's why I put my email address in my profile.

bigdict

Why are you assuming bad faith?

__Joker

Really sorry, if the question came as snarky or if otherwise. Those were not my intent.

Related to AI given all around noise, really wanted to understand kind of contrarian view of monetary aspects.

Once again, apologies if the question seems frivolous.

null

[deleted]

ajb

So they massively reduce the area lost to defects per wafer, from 361 to 2.2 square mm. But from the figures in this blog, this is massively outweighed by the fact that they only get 46222 sq mm useable area out of the wafer, as opposed to 56247 that the H100 gets - because they are using a single square die instead of filling the circular wafer with smaller square dies, they lose 10,025 sq mm!

Not sure how that's a win.

Unless the rest of the wafer is useable for some other customer?

nine_k

It's a win because they have to test one chip, and don't have to spend resources on connecting the chiplets. The latter costs a lot (though it has other advantages). I suspect that a chiplet-based device with total 900k cores would just be not viable due to the size constraints.

If their routing around the defects is automated enough (given the highly regular structure), it may be a massive economy of efforts on testing and packaging the chip.

ungreased0675

Why does it have to be a square? There’s no need to worry about interchangeable third-party heat sink compatibility. Is it possible to make it an irregular polygon instead of square?

kristjansson

Additional wafer area would be a marginal increase in performance (+~20% core core best case) but increases the complexity of their design, and requires they figure out how to package/connect/house/etc. a non-standard shape. A wafer scale chip is already a huge tech risk, why spend more novelty budget on nonessential weirdness?

Scaevolus

Why does their chip have to be rectangular, anyways? Couldn't they cut out a (blocky) circle too?

Qwertious

You need a rectilinear polygon that tessellates, and has the fewest sides possible to minimize the number of cuts necessary. And it would probably help the cutting if the shape is entirely convex, so that cuts can overshoot a bit without damaging anything.

That suggests a rectangle is the only possible shape.

CorrectHorseBat

If it's just one chip per wafer, why even bother cutting?

timerol

Why does it need to tessellate if there's only one chip per wafer?

nine_k

Rather I wonder why do they even need to cut the extra space, instead of putting something there. I suppose that the structure of the device is highly rectangular from the logical PoV, so there's nothing useful to put there. I suspect smaller unrelated chips can be produced on these areas along the way.

guyzero

I've never cut a wafer, but I assume cutting is hard and single straight lines are the easiest.

sroussey

I wonder if you could… just not cut the wafer at all??

yannyu

The cost driver for fabbing out wafers is the number of layers and the number of usable devices per wafer. Higher layer count increases cost and tends to decrease yield, and more robust designs with higher yields increase usable devices per wafer. If circles or other shapes could help with either of those, they would likely be used. Generally the end goal is to have the most usable devices per wafer, so they'll be packed as tightly as possible on the wafer so as to have the highest potential output.

Scaevolus

Right, but they're making just one usable device per wafer already.

null

[deleted]

olejorgenb

Is the wafer itself so expensive? I assume they don't pattern the unused area, so the process should be quicker?

addaon

> I assume they don't pattern the unused area

I’m out of date on this stuff, so it’s possible things have changed, but I wouldn’t make that assumption. It is (used to be?) standard to pattern the entire wafer, with partially-off-the-wafer dice around the edges of the circle. The reason for this is that etching behavior depends heavily on the surrounding area — the amount of silicon or copper whatever etched in your neighborhood affects the speed of etching for you, which effects line width, and (for a single mask used for the whole wafer) thus either means you need to have more margin on your parameters (equivalent to running on an old process) or have a higher defect right near the edge of the die (which you do anyway, since you can only take “similar neighborhood” so far). This goes as far as, for hyper-optimized things like SRAM arrays, leaving an unused row and column at each border of the array.

kurthr

All the process steps are limited by wafers for hour. Lithography (esp EUV) might be slightly faster, but that's not 30% of total steps, since you generally have deposit and etch/implant for every lithography step.

It's close to a dead loss in process cost.

yannyu

> I assume they don't pattern the unused area, so the process should be quicker?

The primary driver of time and cost in the fabrication process is the number of layers for the wafers, not the surface area, since all wafers going through a given process are the same size. So you generally want to maximize the number of devices per wafer, because a large part of your costs will be calculated at the per-wafer level, not a per-device level.

mattashii

Yes, but isn't a big driver of layer costs the cost of the machines to build those layers?

For patterning, a single iteration could be (example values, no actual values used, probably only ballpark accuracy) on a 300M$ EUV machine with 5-year write off cycle, patterns on average 180 full wafers /hour. Excluding energy usage and service time, each wafer that needs full patterning would cost ~38$. If each wafer only needed half the area patterned, the lithography machine might only spend half its usual time on such a wafer, and that could double the throughput of the EUV machine, halving the write-off based cost component of such a patterning step.

Given that each layer generally consists of multiple patterning steps, a 10-20% reduction in those steps could give a meaningful reduction in time spent in the machines whose time spend on the wafer depends on the used wafer area.

This of course doesn't help reduce time in polishing or etching (and other steps that happen with whole wafers at a time), so it won't be as straightforward as % reduction in wafer area usage == % reduction in cost, but I wouldn't be surprised if it was a meaningful percentage.

olejorgenb

Yes, but my understanding is that the wafer is exposed in multiple steps, so there would still be less exposure steps? Probably insignificant compared to all the rest though. (Etching, moving the wafer, etc.)

EDIT: to clarify - I mean the exposure of one single pattern/layer is done in multiple steps. (https://en.wikipedia.org/wiki/Photolithography#Projection)

pulvinar

There's also no reason they couldn't pattern that area with some other suitable commodity chips. Like how sawmills and butchers put all cuts to use.

sitkack

Often those areas are used for test chips and structures for the next version. They are effectively free, so you can use them to test out ideas.

ajb

Good question. I think the wafer has a cost per area which is fairly significant, but I don't have any figures. There has historically been a push to utilise them more efficiently, eg by building fabs that can process larger wafers. Although mask exposure would be per processed area, I think that there are also some proportion of processing time which is per wafer, so the unprocessed area would have an opportunity cost relating to that.

kristjansson

AIUI Wafer marginal cost is lower than you'd expect. I had $50k in my head, quick google indicates[1] maybe <$20k at AAPL volumes? Regardless seems like the economics for Cerebras would strongly favor yield over wafer area utilization.

[1] https://www.tomshardware.com/tech-industry/tsmcs-wafer-prici...

null

[deleted]

georgeburdell

They probably pattern at least next nearest neighbors for local uniformity. That’s just litho though. The rest of the process is done all at once on the wafer

sroussey

It’s a win if you can use the wafer as opposed to throwing it away.

kristjansson

A win is a manufacturing process that results in a functioning product. Wafers, etc. aren't so scarce as to demand every mm2 be used on every one every time.

NickHoff

Neat. What about power density?

An H100 has a TDP of 700 watts (for the SXM5 version). With a die size of 814 mm^2 that's 0.86 W/mm^2. If the cerebras chip has the same power density, that means a cerebras TDP of 37.8 kW.

That's a lot. Let's say you cover the whole die area of the chip with water 1 cm deep. How long would it take to boil the water starting from room temperature (20 degrees C)?

amount of water = (die area of 46225 mm^2) * (1 cm deep) * (density of water) = 462 grams

energy needed = (specific heat of water) * (80 kelvin difference) * (462 grams) = 154 kJ

time = 154 kJ / 39.8 kW = 3.9 seconds

This thing will boil (!) a centimeter of water in 4 seconds. A typical consumer water cooler radiator would reduce the temperature of the coolant water by only 10-15 C relative to ambient, and wouldn't like it (I presume) if you pass in boiling water. To use water cooling you'd need some extreme flow rate and a big rack of radiators, right? I don't really know. I'm not even sure if that would work. How do you cool a chip at this power density?

Paul_Clayton

The enthalpy of vaporization of water (at standard pressure) is listed by Wikipedia[1] as 2.257 kJ/g, so boiling 462 grams would require an additional 1.04 MJ, adding 26 seconds. Cerebras claims a "peak sustained system power of 23kW" for the CS-3 16 Rack Unit system[2], so clearly the power density is lower than for an H100.

[1] https://en.wikipedia.org/wiki/Enthalpy_of_vaporization#Other... [2] https://cerebras.ai/product-system/

twic

On a tangent: has anyone built an active cooling system which operates in a partial vacuum? At half atmospheric pressure, water boils at around 80 C, which i believe is roughly the operating temperature for a hard-working chip. You could pump water onto the chip, have it vapourise, taking away all that heat, then take the vapour away and condense it at the fan end.

This is how heat pipes work, i believe, but heat pipes aren't pumped, they rely entirely on heat-driven flow. I would have thought there were pumped heat pipes. Are they called something else?

It's also not a refrigerator, because those use a pump to pressurise the coolant in its gas phase, whereas here you would only be pumping the water.

pants2

No need to bother with a partial vacuum when ethanol boils at around 80 C as well and doesn't destroy electronics. I'm not aware of any active cooling systems utilizing this though.

TehCorwiz

I found this review from 2019 of mechanically pumped heat pipe technologies. I skimmed the intro. Looks like it already has a foothold in aerospace.

https://www.sciencedirect.com/science/article/abs/pii/S13594...

Dylan16807

> This is how heat pipes work, i believe, but heat pipes aren't pumped, they rely entirely on heat-driven flow. I would have thought there were pumped heat pipes.

Do you have a particular benefit in mind that a pump would help with?

jwan584

A good talk on how Cerebras does power & cooling (8min) https://www.youtube.com/watch?v=wSptSOcO6Vw&ab_channel=Appli...

throwup238

The machine that actually holds one of their wafers is almost as impressive as the chip itself. Tons of water cooling channels and other interesting hardware for cooling.

flopsamjetsam

Minor correction, the keynote video says ~20 kW

lostlogin

If rack mounted, you are ending up with something like a reverse power station.

So why not use it as an energy source? Spin a turbine.

kristjansson

If you let the chip actual boil enough water to run a turbine you're going to have a hard time keeping the magic smoke inside. Much better to run at reasonable temps and try to recover energy from the waste heat.

ericye16

What if you chose a refrigerant with a lower boiling point?

renhanxue

There's a bunch of places in Europe that use waste heat from datacenters in district heating systems. Same thing with waste heat from various industrial processes. It's relatively common practice.

sebzim4500

If my very stale physics is accurate then even with perfect thermodynamic efficiency you would only recover about a third of the energy that you put into the chips.

dylan604

1/3 > 0, so even if you don't get a $0 energy bill I'd venture that any company that could get 1/3 of energy bill would be happy

bentcorner

I'm aware of the efficiency losses but I think it would be amusing to use that turbine to help power the machine generating the heat.

twic

Hey, we're building artificial general intelligence, what's a little perpetual motion on the side?

highfrequency

To summarize: localize defect contamination to a very small unit size, by making the cores tiny and redundant.

Analogous to a conglomerate wrapping each business vertical in a limited liability veil so that lawsuits and bankruptcy do not bring down the whole company. The smaller the subsidiaries, the less defect contamination but also the less scope for frictionless resource and information sharing.

oksurewhynot

I live in a small city/large town that has a large number of craft breweries. I always marveled at how these small operations were able to churn out so many different varieties. Turns out they are actually trying to make their few core recipes but the yield is so low they market the less consistent results as...all that variety I was so impressed with.

bee_rider

> Second, a cluster of defects could overwhelm fault tolerant areas and disable the whole chip.

That’s an interesting point. In architecture class (which was basic and abstract so I’m sure Cerebras is doing something much more clever), we learned that defects cluster, but this is a good thing. A bunch of defects clustering on one core takes out the core, a bunch of defects not clustering could take out… a bunch of cores, maybe rendering the whole chip useless.

I wonder why they don’t like clustering. I could imagine in a network of little cores, maybe enough defects clustered on the network could… sort of overwhelm it, maybe?

Also I wonder how much they benefit from being on one giant wafer. It is definitely cool as hell. But could chiplets eat away at their advantage?

IshKebab

TSMC also have a manufacturing process used by Tesla's Dojo where you can cut up the chips, throw away the defective ones, and then reassemble working ones into a sort of wafer scale device (5x5 chips for Dojo). Seems like a more logical design to me.

bee_rider

Is this similar to a chiplet design? Chiplets have been a thing for a while, so I assume Cerebras avoided them on purpose.

IshKebab

I don't think so - chiplets are much smaller and I think the process is different.

ryao

I had been under the impression that Nvidia had done something similar here, but they did not talk about deploying the space saving design and instead only talked about the server rack where all of the chips on the mega wafer normally are.

https://www.sportskeeda.com/gaming-tech/what-nvlink72-nvidia...

wmf

That shield is just a prop that looks nothing like the real product. The NVL72 rack doesn't use any wafer-scale-like packaging.

ryao

It would be nice if they made it real. The cost savings from not needing so much material should be fantastic.

mhh__

Amazing. I clicked a button in the azure deployment menu today...

ilaksh

I assume people are aware, but Cerebras has a web demo and API which is open to try and it is 2000 tokens per second for Llama 3.3 70b and 1000 tokens per second for Llama 3.1 405b.

https://cerebras.ai/inference

Neywiny

Understanding that there's inherent bias by them being competitors of the other companies, but still this article seems to make some stretches. If you told me you had an 8% core defect rate reduced 100x, I'd assume you got to close to 99% enablement. The table at the end shows... Otherwise.

They also keep flipping between cores, SMs, dies, and maybe other block sizes. At the end of the day I'm not very impressed. They seemingly have marginally better yields despite all that effort.

sfink

I think you're missing the point. The comparison is not between 93% and 92%. The comparison is between what they're getting (93%) and what you'd get if you scaled up the usual process to the core size they're using (0%). They are doing something different (namely: a ~whole wafer chip) that isn't possible without massively boosting the intra-chip redundancy. (The usual process stops working once you no longer have any extra dies to discard.)

> Despite having built the world’s largest chip, we enable 93% of our silicon area, which is higher than the leading GPU today.

The important part is building the largest chip. The icing on the top is that the enablement is not lower. Which it would be without the routing-to-spare-cores magic sauce.

And the differing terminology is because they're talking about differing things? You could call an SM a core, but it kind of contains (heterogeneous) cores itself. (I've no idea whether intra-SM cores can be redundant to boost yield.) A die is the part you break off and build a computer out of, it may contain a bunch of cores, a wafer can be broken up into multiple dies but for Cerebras it isn't.

If NVIDIA were to go and build a whole-wafer die, they'd do something similar. But Cerebras did it and got it to work. NVIDIA hasn't gotten into that space yet, so there's no point in building a product that you can't sell to a consumer or even a data center that isn't built around that exact product (or to contain a Balrog).

Neywiny

I think I'll still stand by my viewpoint. They said:

> On the Cerebras side, the effective die size is a bit smaller at 46,225mm2. Applying the same defect rate, the WSE-3 would see 46 defects. Each core is 0.05mm2. This means 2.2mm2 in total would be lost to defects.

So ok they claim that they should see (46225-2.2)/46225 = 99.995%. Doing the same math for their Nvidia numbers it's 99.4%. And yet in practice neither approach got to these numbers. Nowhere near it. I just feel like the whole article talks about all this theory and numbers and math of how they're so much better but in practice it's meaningless.

So what I'm not seeing is why it'd be impossible for all the H100s on a wafer to be interconnected and call it a day. You'd presumably get 92/93 = 98.9% of the performance and, here's the kicker, no need to switch to another architecture. I didn't know where your 0% number came from. Nothing about this article says that a competitor doing the same scaling to wafer scale would get 0%, just a marginal decrease in how many cores made it through fab.

Fundamentally I am not convinced from this article that Cerebras has done something in their design that makes this possible. All I'm seeing is that it'd perform 1% faster.

Edit: thinking a bit more on it, to me it's like they said TSMC has a guy with a sledgehammer who smashes all the wafers and their architecture snaps a tiny bit cleaner. But they haven't said anything about firing the guy with the sledgehammer. Their paragraph before the final table says that this whole exercise is pretty much meaningless because their numbers are made up about competitors and they aren't even the right numbers to be using. Then the table backs up my paraphrase.

fspeech

There is nothing inherently good about wafer scale. It's actually harder to dissipate heat and enable hybrid bonding with DRAM. So the gp is entirely correct that you need to actually show higher silicon utilization to be even considered as being something worthwhile.

exabrial

I have a dumb question. Why isn't silicon sold in cubes instead of cylinders?

amelius

The silicon ingots have a rotating production process that results in cylinders, not bricks.

exabrial

fascinating, I figured it was something like that. maybe we should produce hexagonal, instead of square, chip designs

kryptiskt

Crystalline silicon is produced with the Czochralski process (https://en.wikipedia.org/wiki/Czochralski_method), which produces a round ingot. So you'd have to cut away perfectly fine silicon to make something squarish.

bigmattystyles

no matter how you orient a circle on a plane, it's the same

anonymousDan

Very interesting. Am I correct in saying that fault tolerance here is with respect to 'static' errors that occur during manufacturing and are straightforward to detect before reaching the customer? Or can these failures potentially occur later on (and be tolerated) during the normal life of the chip?

aaroninsf

The number of people ITT this thread who have absorbed the world-weary AI-is-a-bubble skepticism...

I'm just gonna say, with serene certainty,

the economic order we inhabit going through phase change is certain. From certain myopic perspectives we can shoehorn that into a narrative of cyclical patterns in the tech industry or financial markets etc etc.

This is not going to be that. No more than the transformation of American retail can be shoehorned to kind of look like it used if you don't know anything at all about what contemporary international trade and logistics and oligopoly actually mean in terms of what is coming into your home from where and why it is or isn't cheap.

Where we'll be in 10, 20, years is literally unimaginable today; and trying to navigate that wrt traditional landmarks... oof.