Probably fun for those who already bought DDR5 memory... still kicking myself for not just pulling the trigger on that 128GB dual stick kit I looked at for $600 back in September. Now it's listed at $4k...
Meanwhile I hope my AM4 will chug along a few more years.
If you don't need 128GB, there are quality 64GB kits for under $700 on Newegg right now, which is cheaper than this CPU.
If someone needs to build something now and can wait to upgrade RAM in a year or two, 32GB kits are in the $370 range.
I don't like this RAM price spike either, but in the context of building a high-end system with a 16-core flagship CPU like this and probably an expensive GPU, it's still reasonable to build a system. If you must have 128GB of RAM it can be done with bundles like the one I linked above but I'd recommend waiting at least 6 months if you can. There are signs that prices are falling now that panic-buying has started to trail off.
128GB of RAM should not cost $4K even in this market.
In January I upgraded my desktop, 9950X3D £600, 64GB DDR5-6000 £600, MSI MAG Tomahawk X870E £300, Samsung 990 Pro 4TB £350, Asus Prime 9070XT £580. I spent a another £250 on PSU and cooler and reused my case (Phanteks Evolv Enthoo TG, beautiful case but horrible cooling. Will cut some holes in it and if it doesnt work out look for something with more airflow).
The RAM price was already inflated at that time, and the same kit is now £800, but in October or earlier last year I'd have saved possibly the cost of the CPU/GPU on the whole thing, but now it's be about the cost of a CPU/GPU more expensive.
On a side note for anyone not aware, 9950X3D isn't the best choice for pure gaming, 9850X3D is cheaper and marginally better, also I went with 2 sticks of RAM kit, 4 sticks is much harder to run at the advertised speed (6000) which is actually an overclock.
Im a dev and a linux user/gamer hence my choice of CPU/GPU.
No such bundle deals where I am. Absolute cheapest DDR5 128GB kit around is 2 sticks of 5600 64GB for $2k.
Cheapest 64GB kit is $930.
The kit I was oh-so-close to buying was two 6400 64GB sticks.
Not gonna buy now, not that desperate. I have a spare AM4 board, DDR4 memory and heck even CPU, I'll ride this one out. Likely skip AM5 entirely if something doesn't drastically change.
> Absolute cheapest DDR5 128GB kit around is 2 sticks of 5600 64GB for $2k.
That's not far from the bundle deal above, once you subtract the $700 CPU.
If you really need 128GB the 5600 kit is fine. Having 208MB of total cache on the CPU means the real world difference between a 5600 kit and a slightly faster kit is negligible in most use cases.
If you don't need to upgrade then clearly don't force an upgrade right now. I just wanted to comment that $4K for 128GB of RAM is a very bad price right now, even with the current situation.
I really want a x3d because a game I play is heavily single threaded, I have the income and the financial stability but I can't in any good conscious upgrade to am5 with the ram prices. It's insane
AMD had an upgrade path with the 5700x3d, assuming you’re on AM4.
Just reading now that they went out of production half a year ago which is a shame. I was very impressed being able to upgrade with the same motherboard 6 years down the line.
I'm the mythical customer who went from a 1700X in a B350 motherboard near launch day to a 5800X3D in the same board (after a dozen BIOS updates). Felt amazing. Like the old 486DX2 days.
Same! Kept checking back for bios updates and even years later they kept announcing more support! Truly crazy.
Other than the speed it’s a very good reason to go with amd, the upgrade scope is massive, on am5 you can go from a 6 core and soon all the way to a 24 core with the new zen6
I can't imagine it's looking good in the consumer space, but server space seems to be lit[1]:
Su said that typically, the first quarter (Q1) is slower due to seasonal patterns, but AMD has seen its data center business expand from Q4 into Q1, demonstrating ongoing strength across both CPUs and GPUs. This growth underscores the company’s ability to capitalize on rising demand for AI compute and enterprise workloads, even during traditionally quieter periods.
“We are going into a big inflection year here in 2026. The CPU business is absolutely on fire.”
> Probably fun for those who already bought DDR5 memory
Nah, those of us who already bought DDR5 memory also already bought decent CPUs. Dropping another $1k for these incremental gains would be silly. It'd make a lot more sense if DDR5 had been around longer so that people had the option to make generational upgrades to this CPU but DDR5 on AMD has only been around for Zen4 and Zen5.
I'm looking at building a new system, and was waiting to see what happens with this chip and Intel's Arc Pro B70 card. I can't find ECC UDIMMs of 64GB per-stick to make 128GB, but I can put together two solo UDIMMs of 32GB or 48GB for $800 and $1000 per stick respectively.
I really want to see what enabling the L3 cache options in the BIOS do from a NUMA standpoint. I have some projects I want to work on where being able to even just simulate NUMA subdivisions would be highly useful.
>Meanwhile I hope my AM4 will chug along a few more years.
I am fine with my 2 year old 128GB DDR4 for now. I will just upgrade the 14700K to 14900KS CPU and wait 2 more years.
Judging by the benchmarks newer CPUs aren't much better for multithreading workloads than 14900KS anyway, so it doesn't make a lot of sense to upgrade to newer CPUs, DDR5 and a new mobo.
After randomly breaking the AM4 CPU and motherboard in my 4 year old PC last year and seeing that at the time I'd spent almost a new PC to get new parts and rebuild it. Less if I wanted to do a complete rebuild myself but I'm over building PCs. I've done that for years.
It was an expensive mistake as I bought a few options to experiment including a NUC and an M4 Mac Mini but eventually bought a 9800X3D 5070Ti PC for <$2 and for no reason in particular I bought a 64GB DDR5-6000 kit for $200 in August or so. I checked recently and that kit is pushing $1000. I also bought a 4080 laptop and bought a 64GB kit and an extra SSD for it too last year.
That's pretty lucky given what's happened since. I don't claim any kind of foresight about what would happen.
I do kind of want to take the parts I have and build another AM4 PC. The 5900XT is not a bad option with 16 cores for ~$300 but my DDR4 RAM is almost useless because the best deals now are for combos of CPU + motherboard + RAM at steep discounts.
You can get some good deals on prebuilts still. Not as good as 6+ months ago but still not bad. Costco has a 5080 PC for $2300. There's no way I'm going overboard and building a 128GB+ PC right now.
I've seen multiple RAM spikes. We had one at the height of the crypto hysteria IIRC but this is significantly worse and is also impacting SSDs. I kinda wish I'd bought 1-2 4TB+ SSDs last year but oh well.
We're really waiting for the AI bubble to pop. Part of me think sthat'll be in the next year but it could stay irrational substantially longer than that.
The C30 64GB kits are nearly impossible to buy now, so, well done. Got one in September '23 for ~$380 AUD, on the rare occasions it's available today it's been over $1600 AUD.
I upgraded my UPS to a sine interactive unit to minimise the risk of it dying to bad power while the market is so crazy...
Context: Early in the firmware boot process the memory controller isn't configured yet so the firmware uses the cache as RAM. In this mode cache lines are never evicted since there's no memory to evict them to.
There may be server workloads for which the L3 cache is sufficient, would be interesting if it made sense to create boards for just the CPU and no memory at scale.
I imagine for such a workload you can always solder a small memory chip to avoid having to waste L3 on unused memory and a non-standard booting process so probably not.
Most definitely, I work in finance and optimizing workloads to fit entirely in cache (and not use any memory allocations after initialization) is the de-facto standard of writing high perf / low latency code.
Lots of optimizations happening to make a trading model as small as possible.
I remember the talk about the Wii/WiiU hacking they intentionally kept the early boot code in cache so that the memory couldn’t be sniffed or modified on the ram bus which was external to the CPU and thus glitchable.
In my case it began with 16K (yes, 161024 bytes) and 90K (yes, 901024 bytes) 5.25" floppy disks (although the floppies were a few months after the computer). Eventually upgraded to 48K RAM and 180K double density floppy disks. The computer: Atari 800.
I'll see your Atari 800 and raise you my Atari 2600 with its whopping 128 bytes of RAM. Bytes with a B. I can kinda sorta call it a computer because you could buy a BASIC cartridge for it (I didn't and stand by that decision - it was pretty bad).
KolibriOS would fit in there, even with the data in memory. You cannot load it into the cache directly, but when the cache capacity is larger than all the data you read there should be no cache eviction and the OS and all data should end up in the cache more or less entirely. In other words it should be really, really fast, which KolibriOS already is to begin with.
That assumes KolibriOS or any major component is pinned to one core and one cache slice instead of getting dragged between CCDs or losing memory affinity. Throw actual users, IO, and interrupts at it and you get traffic across chiplets, or at least across L3 groups, so the nice 'everything lives in cache' story falls apart fast.
Nice demo, bad model. The funny part is that an entire OS can fit in cache now, the hard part is making the rest of the system act like that matters.
Unless you lay everything out continuously in memory, you’ll still get cache eviction due to associativty and depending on the eviction strategy of the CPU. But certainly DOS or even early Windows 95 could conceivably just run out of the cache
Windows 95 only needed 4MB RAM and 50 MB disk, so that's certainly doable. The trick is to have a hypervisor spread that allocation across cache lines.
Yeah, cache eviction is the reason I was assuming it is "probably not possible architecturally", but I also figured there could be features beyond my knowledge that might make it possible.
Edit: Also this 192MB of L3 is spread across two Zen CCDs, so it's not as simple as "throw it all in L3" either, because any given core would only have access to half of that.
Well, yeah, reality strikes again. All you need is an exploit in the microcode to gain access to AMD's equivalent to the ME and now you can just map the cache as memory directly. Maybe. Can microcode do this or is there still hardware that cannot be overcome by the black magic of CPU microcode?
Maybe in 50 years the cache of CPUs and GPUs will be 1TB. Enough to run multiple LLMs (a model entirely run for each task). Having robots like in the movies would need LLMs much much faster than what we see today.
The extra cache doesn't do a damn thing (maybe +2%)
The lower leakage currents at lower voltages allowed them to implement a far more aggressive clock curve from the factory. That's where the higher allcore clock comes from (+30W TDP)
I'm not complaining at all, I think this is an excellent way to leverage binning to sell leftover cache.
Though if I may complain, Ars used to actually write about such things in their articles instead of speculate in a way that suspiciously resembles what an AI would write.
> The extra cache doesn't do a damn thing (maybe +2%)
It depends on the task. For some memory-bound tasks the extra cache is very helpful. For CFD and other simulation workloads the benefits are huge.
For other tasks it doesn't help at all.
If someone wants a simple gaming CPU or general purpose CPU they don't need to spend the money for this. They don't need the 16-core CPU at all. The 9850X3D is a better buy for most users who aren't frequently doing a lot of highly parallel work
It really doesn't. In virtually every case the work is being completed faster than the cache can grow to that size. What little gains are being realized are from not having to wait for cores with access to the cache to become available.
It's also useful to point out that the use cases and workloads where SDCI are most beneficial are far, far beyond the scope of what anyone will have installed in a Zen rig. Dual 100G networking cards? The cost of both of those damn near buys all of a 9950X3D2 setup.
> Here is the side-by-side of the Ryzen 9 9950X vs. 9950X3D for showing the areas where 3D V-Cache really is helpful:
Coincidentally, it looks they filtered to all benchmarks with differences greater than 2%. The biggest speedup is 58.1%, and that's just 3d vcache on half the chip.
On AMD the L3 cache is partitioned between the 2 chiplets.
So for 9950X3D half of the cores use a small L3 cache.
For applications that use all 16 cores, the cases where X3D2 provides a great benefit will be much more frequent than for a hypothetical CPU where the same cache increase would have been applied to a unified L3 cache.
The threads that happen to be scheduled on the 2nd chiplet will have a 3 times bigger L3 cache, which can enhance their performance a lot and many applications may have synchronization points where they wait for the slowest thread to finish a task, so the speed of the slowest thread may have a lot of influence on the performance.
Agree. The article's 2nd para notes "AMD relies on its driver software to make sure that software that benefits from the extra cache is run on the V-Cache-enabled CPU cores, which usually works well but is occasionally error-prone." - in regard to the older, mixed-cache-size chips.
> I'm curious to see...
Yeah - though I don't expect current-day Ars Technica will bother digging that deep. It could take some very specialized benchmarks to show such large gains.
Some of their writers, who are quite excellent, still do. Others just seem to regurgitate press releases with very little useful investigation.
How critical of the lazy writers I am may seem outsized, but I grew up reading and learning from the much better version of Ars -one I used to subscribe to.
The gain is very workload dependent, so there are no generally-applicable rules.
There are many applications which need synchronization between threads, so the speed of the slowest thread has a disproportionate influence on the performance.
In such applications, on X3D2 the slowest thread has a 3 times bigger cache on an X3D2 vs. X3D. That can make a lot of difference.
So there will be applications with no difference in performance, but also applications with a very large difference in performance, equal to the best performance differences shown by X3D vs. plain 9950X.
That's what's different about this one. "Enter the Ryzen 9 9950X3D2 Dual Edition, a mouthful of a chip that includes 64MB of 3D V-Cache on both processor dies, without the hybrid arrangement that has defined the other chips up until now."
Given that the dies still have L3 on them does this count as L4 or does the hardware treat it as a single pool of L3?
Would be neat to have an additional cache layer of ~1 GB of HBM on the package but I guess there's no way that happens in the consumer space any time soon.
Per compute die it functions as one 96M L3 with uniform latency. It is 4 cycles more latency than the configuration with smaller 32M L3. But there are two compute dies, each with their own L3. And like the 9950X coherency between these two L3 is maintained over global memory interconnect to the third (IO) die.
But to do it literally - I'm not a low-level motherboard EE, but I'd bet you're looking at 5 to 7 figures (US $) of engineering work, to get around all the ways in which that would violate assumptions baked into the designs of the CPU, support chips, firmwares, etc.
Make a fake ram which offers write through guarantee and returns bus no matter what address is referenced. You could possibly short circuit any "is ram there" test if it just says yes for whatever size and stride got configured.
Makes sense. RAM pricing surely has lead to a fall of AM5 high-end CPU purchases, might as well try to get some extra cash from those who still buy. Bin the remaining now non-X3D chips as something else.
Probably fun for those who already bought DDR5 memory... still kicking myself for not just pulling the trigger on that 128GB dual stick kit I looked at for $600 back in September. Now it's listed at $4k...
Meanwhile I hope my AM4 will chug along a few more years.
> Now it's listed at $4k...
You can buy 128GB of DDR5-6000 with a 9950X3D (not this newest X2 version, but still a $699 CPU) and a motherboard and a case for $2800 right now: https://www.newegg.com/Product/ComboDealDetails?ItemList=Com...
If you don't need 128GB, there are quality 64GB kits for under $700 on Newegg right now, which is cheaper than this CPU.
If someone needs to build something now and can wait to upgrade RAM in a year or two, 32GB kits are in the $370 range.
I don't like this RAM price spike either, but in the context of building a high-end system with a 16-core flagship CPU like this and probably an expensive GPU, it's still reasonable to build a system. If you must have 128GB of RAM it can be done with bundles like the one I linked above but I'd recommend waiting at least 6 months if you can. There are signs that prices are falling now that panic-buying has started to trail off.
128GB of RAM should not cost $4K even in this market.
$2800 is still a huge price in comparison with the last year.
Last summer, a 9950X3D + motherboard + cooler + 128 GB DRAM + VAT sales taxes was the equivalent of $1400 in Europe, where I live.
That's half of your quoted price. That was without case and PSU, but adding e.g. $200 for those would not change much.
In January I upgraded my desktop, 9950X3D £600, 64GB DDR5-6000 £600, MSI MAG Tomahawk X870E £300, Samsung 990 Pro 4TB £350, Asus Prime 9070XT £580. I spent a another £250 on PSU and cooler and reused my case (Phanteks Evolv Enthoo TG, beautiful case but horrible cooling. Will cut some holes in it and if it doesnt work out look for something with more airflow).
The RAM price was already inflated at that time, and the same kit is now £800, but in October or earlier last year I'd have saved possibly the cost of the CPU/GPU on the whole thing, but now it's be about the cost of a CPU/GPU more expensive.
On a side note for anyone not aware, 9950X3D isn't the best choice for pure gaming, 9850X3D is cheaper and marginally better, also I went with 2 sticks of RAM kit, 4 sticks is much harder to run at the advertised speed (6000) which is actually an overclock.
Im a dev and a linux user/gamer hence my choice of CPU/GPU.
I bought 192GB (4x 48GB) of DDR5-6400 for 299 euro in September but returned it because I couldn't get 4 DIMMS to run at decent speeds in the system.
6 or so weeks after I returned it the kit was listed at 1499.
Yeah the only way to run 4 sticks of DDR5 decently is with Intel. It's a bit of a shame that you can't cram enough RAM to run big models.
The most I could get running on 10GB VRAM + 96GB RAM was a REAP'd + quantized version of MiniMax-M2.5
Threadripper is a good alternative. No point having a lot of dual channel ram for LLMs, too slow
No such bundle deals where I am. Absolute cheapest DDR5 128GB kit around is 2 sticks of 5600 64GB for $2k.
Cheapest 64GB kit is $930.
The kit I was oh-so-close to buying was two 6400 64GB sticks.
Not gonna buy now, not that desperate. I have a spare AM4 board, DDR4 memory and heck even CPU, I'll ride this one out. Likely skip AM5 entirely if something doesn't drastically change.
> Absolute cheapest DDR5 128GB kit around is 2 sticks of 5600 64GB for $2k.
That's not far from the bundle deal above, once you subtract the $700 CPU.
If you really need 128GB the 5600 kit is fine. Having 208MB of total cache on the CPU means the real world difference between a 5600 kit and a slightly faster kit is negligible in most use cases.
If you don't need to upgrade then clearly don't force an upgrade right now. I just wanted to comment that $4K for 128GB of RAM is a very bad price right now, even with the current situation.
> I just wanted to comment that $4K for 128GB of RAM is a very bad price right now
Oh absolutely. Just mentioned it since I was very close to buying it back then, and now it's completely bonkers.
That bundle deal is quite well priced all things considered, it basically prices the memory where it was. Again, sadly no great bundle deals here.
I really want a x3d because a game I play is heavily single threaded, I have the income and the financial stability but I can't in any good conscious upgrade to am5 with the ram prices. It's insane
Yep exactly the same situation.
I would not be surprised if we see casualties in adjacent markets, such as motherboards, coolers and whatnot.
AMD had an upgrade path with the 5700x3d, assuming you’re on AM4.
Just reading now that they went out of production half a year ago which is a shame. I was very impressed being able to upgrade with the same motherboard 6 years down the line.
I'm the mythical customer who went from a 1700X in a B350 motherboard near launch day to a 5800X3D in the same board (after a dozen BIOS updates). Felt amazing. Like the old 486DX2 days.
Same! Kept checking back for bios updates and even years later they kept announcing more support! Truly crazy.
Other than the speed it’s a very good reason to go with amd, the upgrade scope is massive, on am5 you can go from a 6 core and soon all the way to a 24 core with the new zen6
What game, if you don't mind my asking?
World of Warcraft
Wonder how much sales amd and intel are losing because of tight DDR5 supply
I can't imagine it's looking good in the consumer space, but server space seems to be lit[1]:
Su said that typically, the first quarter (Q1) is slower due to seasonal patterns, but AMD has seen its data center business expand from Q4 into Q1, demonstrating ongoing strength across both CPUs and GPUs. This growth underscores the company’s ability to capitalize on rising demand for AI compute and enterprise workloads, even during traditionally quieter periods.
“We are going into a big inflection year here in 2026. The CPU business is absolutely on fire.”
[1]: https://stocktwits.com/news-articles/markets/equity/amd-ceo-...
oh wow you weren't joking: https://pcpartpicker.com/products/memory/#xcx=0&b=ddr5&Z=131...
(cheapest at $1240 USD)
> Probably fun for those who already bought DDR5 memory
Nah, those of us who already bought DDR5 memory also already bought decent CPUs. Dropping another $1k for these incremental gains would be silly. It'd make a lot more sense if DDR5 had been around longer so that people had the option to make generational upgrades to this CPU but DDR5 on AMD has only been around for Zen4 and Zen5.
I am glad I decisively ordered 96GB (2x48) DDR5 ECC back in June, alongside the 9800x3d.
I hope this is still enough for the planned upgrade to Zen7 in 2028.
I'm looking at building a new system, and was waiting to see what happens with this chip and Intel's Arc Pro B70 card. I can't find ECC UDIMMs of 64GB per-stick to make 128GB, but I can put together two solo UDIMMs of 32GB or 48GB for $800 and $1000 per stick respectively.
I really want to see what enabling the L3 cache options in the BIOS do from a NUMA standpoint. I have some projects I want to work on where being able to even just simulate NUMA subdivisions would be highly useful.
You're basically me. I was mulling 48 vs 96, decided 200$ wasn't worth quibbling too much over and bought 96GB in August.
Feeling pretty chuffed now XD (though still sad because building a new PC is dumb when RAM costs more than a 24 core monster CPU)
Same... got 2x48 DDR5 for $304 back in February of 2025. Equivalent kits are going for $900-$1,100. Madness.
>Meanwhile I hope my AM4 will chug along a few more years.
I am fine with my 2 year old 128GB DDR4 for now. I will just upgrade the 14700K to 14900KS CPU and wait 2 more years.
Judging by the benchmarks newer CPUs aren't much better for multithreading workloads than 14900KS anyway, so it doesn't make a lot of sense to upgrade to newer CPUs, DDR5 and a new mobo.
After randomly breaking the AM4 CPU and motherboard in my 4 year old PC last year and seeing that at the time I'd spent almost a new PC to get new parts and rebuild it. Less if I wanted to do a complete rebuild myself but I'm over building PCs. I've done that for years.
It was an expensive mistake as I bought a few options to experiment including a NUC and an M4 Mac Mini but eventually bought a 9800X3D 5070Ti PC for <$2 and for no reason in particular I bought a 64GB DDR5-6000 kit for $200 in August or so. I checked recently and that kit is pushing $1000. I also bought a 4080 laptop and bought a 64GB kit and an extra SSD for it too last year.
That's pretty lucky given what's happened since. I don't claim any kind of foresight about what would happen.
I do kind of want to take the parts I have and build another AM4 PC. The 5900XT is not a bad option with 16 cores for ~$300 but my DDR4 RAM is almost useless because the best deals now are for combos of CPU + motherboard + RAM at steep discounts.
You can get some good deals on prebuilts still. Not as good as 6+ months ago but still not bad. Costco has a 5080 PC for $2300. There's no way I'm going overboard and building a 128GB+ PC right now.
I've seen multiple RAM spikes. We had one at the height of the crypto hysteria IIRC but this is significantly worse and is also impacting SSDs. I kinda wish I'd bought 1-2 4TB+ SSDs last year but oh well.
We're really waiting for the AI bubble to pop. Part of me think sthat'll be in the next year but it could stay irrational substantially longer than that.
The C30 64GB kits are nearly impossible to buy now, so, well done. Got one in September '23 for ~$380 AUD, on the rare occasions it's available today it's been over $1600 AUD.
I upgraded my UPS to a sine interactive unit to minimise the risk of it dying to bad power while the market is so crazy...
Crazy to think that my first personal computer's entire storage (was 160MB IIRC?) could fit into the L3 of a single consumer CPU!
It's probably not possible architecturally, but it would be amusing to see an entire early 90's OS running entirely in the CPU's cache.
My first pc had 40MB :D
https://github.com/coreboot/coreboot/blob/main/src/soc/intel...
Context: Early in the firmware boot process the memory controller isn't configured yet so the firmware uses the cache as RAM. In this mode cache lines are never evicted since there's no memory to evict them to.
There may be server workloads for which the L3 cache is sufficient, would be interesting if it made sense to create boards for just the CPU and no memory at scale.
I imagine for such a workload you can always solder a small memory chip to avoid having to waste L3 on unused memory and a non-standard booting process so probably not.
Most definitely, I work in finance and optimizing workloads to fit entirely in cache (and not use any memory allocations after initialization) is the de-facto standard of writing high perf / low latency code.
Lots of optimizations happening to make a trading model as small as possible.
I remember the talk about the Wii/WiiU hacking they intentionally kept the early boot code in cache so that the memory couldn’t be sniffed or modified on the ram bus which was external to the CPU and thus glitchable.
In my case it began with 16K (yes, 161024 bytes) and 90K (yes, 901024 bytes) 5.25" floppy disks (although the floppies were a few months after the computer). Eventually upgraded to 48K RAM and 180K double density floppy disks. The computer: Atari 800.
I'll see your Atari 800 and raise you my Atari 2600 with its whopping 128 bytes of RAM. Bytes with a B. I can kinda sorta call it a computer because you could buy a BASIC cartridge for it (I didn't and stand by that decision - it was pretty bad).
My first PC had a 20MB HDD with 512Kb of RAM. So yeah that could fit into cache 10 times now.
Commodore PET for me - 8 KB of RAM and all the data you could store and read back from a TDK 120 cassette tape . . .
* https://en.wikipedia.org/wiki/Commodore_PET
Same time as the Trash-80 and BBC micro were making inroads.
KolibriOS would fit in there, even with the data in memory. You cannot load it into the cache directly, but when the cache capacity is larger than all the data you read there should be no cache eviction and the OS and all data should end up in the cache more or less entirely. In other words it should be really, really fast, which KolibriOS already is to begin with.
That assumes KolibriOS or any major component is pinned to one core and one cache slice instead of getting dragged between CCDs or losing memory affinity. Throw actual users, IO, and interrupts at it and you get traffic across chiplets, or at least across L3 groups, so the nice 'everything lives in cache' story falls apart fast.
Nice demo, bad model. The funny part is that an entire OS can fit in cache now, the hard part is making the rest of the system act like that matters.
Unless you lay everything out continuously in memory, you’ll still get cache eviction due to associativty and depending on the eviction strategy of the CPU. But certainly DOS or even early Windows 95 could conceivably just run out of the cache
Windows 95 only needed 4MB RAM and 50 MB disk, so that's certainly doable. The trick is to have a hypervisor spread that allocation across cache lines.
Yeah, cache eviction is the reason I was assuming it is "probably not possible architecturally", but I also figured there could be features beyond my knowledge that might make it possible.
Edit: Also this 192MB of L3 is spread across two Zen CCDs, so it's not as simple as "throw it all in L3" either, because any given core would only have access to half of that.
Well, yeah, reality strikes again. All you need is an exploit in the microcode to gain access to AMD's equivalent to the ME and now you can just map the cache as memory directly. Maybe. Can microcode do this or is there still hardware that cannot be overcome by the black magic of CPU microcode?
You had ~160,000 times more storage than I did for my first personal computer.
640K ought to be enough for anybody.
Maybe in 50 years the cache of CPUs and GPUs will be 1TB. Enough to run multiple LLMs (a model entirely run for each task). Having robots like in the movies would need LLMs much much faster than what we see today.
IIRC some relatively strange CPUs could run with unbacked cache.
Intel's platform, at the very least, use cache-as-ram during the boot phase before the DDR interface can be trained and started up. https://github.com/coreboot/coreboot/blob/main/src/soc/intel...
> it would be amusing to see an entire early 90's OS running entirely in the CPU's cache.
There’s actually already two running (MINIX and UEFI), and it’s the opposite OS amusing - https://www.zdnet.com/article/minix-intels-hidden-in-chip-op...
I wonder how much faster dos would boot, especially with floppy seek times...
Instantly.
If you run a VM on a CPU like this, using a baremetal hypervisor, you can get very close to "everything in cache".
You can get close with a VM, but there's overhead in device emulation that slows things down.
Consider a VM where that kind of stuff has been removed, like the firecracker hypervisor used for AWS Lambda. You're talking milliseconds.
My first computer whole RAM could fit in L1 of a single core (128k)
The extra cache doesn't do a damn thing (maybe +2%)
The lower leakage currents at lower voltages allowed them to implement a far more aggressive clock curve from the factory. That's where the higher allcore clock comes from (+30W TDP)
I'm not complaining at all, I think this is an excellent way to leverage binning to sell leftover cache.
Though if I may complain, Ars used to actually write about such things in their articles instead of speculate in a way that suspiciously resembles what an AI would write.
> The extra cache doesn't do a damn thing (maybe +2%)
It depends on the task. For some memory-bound tasks the extra cache is very helpful. For CFD and other simulation workloads the benefits are huge.
For other tasks it doesn't help at all.
If someone wants a simple gaming CPU or general purpose CPU they don't need to spend the money for this. They don't need the 16-core CPU at all. The 9850X3D is a better buy for most users who aren't frequently doing a lot of highly parallel work
It really doesn't. In virtually every case the work is being completed faster than the cache can grow to that size. What little gains are being realized are from not having to wait for cores with access to the cache to become available.
But consumer product does not support SDCI (only Epyc Turin supports it), so it does not benefit too much if an accelerator is involved.
It's also useful to point out that the use cases and workloads where SDCI are most beneficial are far, far beyond the scope of what anyone will have installed in a Zen rig. Dual 100G networking cards? The cost of both of those damn near buys all of a 9950X3D2 setup.
It's very workload dependent. It certainly does more than 2% on many workloads.
See https://www.phoronix.com/review/amd-ryzen-9-9950x3d-linux/10
> Here is the side-by-side of the Ryzen 9 9950X vs. 9950X3D for showing the areas where 3D V-Cache really is helpful:
Coincidentally, it looks they filtered to all benchmarks with differences greater than 2%. The biggest speedup is 58.1%, and that's just 3d vcache on half the chip.
I think GP was saying that the additional 3D cache on this chip compared to the standard x3d isn’t going to do much.
I’m curious to see whether the same benchmarks benefit again so greatly.
On AMD the L3 cache is partitioned between the 2 chiplets.
So for 9950X3D half of the cores use a small L3 cache.
For applications that use all 16 cores, the cases where X3D2 provides a great benefit will be much more frequent than for a hypothetical CPU where the same cache increase would have been applied to a unified L3 cache.
The threads that happen to be scheduled on the 2nd chiplet will have a 3 times bigger L3 cache, which can enhance their performance a lot and many applications may have synchronization points where they wait for the slowest thread to finish a task, so the speed of the slowest thread may have a lot of influence on the performance.
> I think GP was saying...
Agree. The article's 2nd para notes "AMD relies on its driver software to make sure that software that benefits from the extra cache is run on the V-Cache-enabled CPU cores, which usually works well but is occasionally error-prone." - in regard to the older, mixed-cache-size chips.
> I'm curious to see...
Yeah - though I don't expect current-day Ars Technica will bother digging that deep. It could take some very specialized benchmarks to show such large gains.
Some of their writers, who are quite excellent, still do. Others just seem to regurgitate press releases with very little useful investigation.
How critical of the lazy writers I am may seem outsized, but I grew up reading and learning from the much better version of Ars -one I used to subscribe to.
9950X3D2? AMD, who is making you name your products like this? At some point just give up and name the chip a UUID already.
I actually don't mind this one, 9950 is the actual chip, x3d is the cache (where it's larger) and the 2 stands for it being on both chiplets.
Like your UUID joke but agree with sibling comment that 9950X3D2 is actually a good name.
can't agree. this name has logical meaning
Breakdown of the (semi-clickbait) 208MB cache: 16MB L2 (8MB per die?) + 32MB L3 * 2 dies + 64MB L3 Stacked 3D V-cache * 2
For comparison, 9950X3D have a total cache of 144MB.
> 16MB L2 (8MB per die?)
It is indeed 8MB per compute die but really 1MB per core. Not shared among the entire CCD.
I wouldn’t be caught dead with less than 200MB of cache in my desktop in 2026.
I don't really see a huge reason to buy this other than it being a top-tier halo product.
For gaming, AMD already pins the game threads to the CCD with the extra cache pretty well.
For multi-threaded workloads the gain from having cache on both CCDs is quite small.
The gain is very workload dependent, so there are no generally-applicable rules.
There are many applications which need synchronization between threads, so the speed of the slowest thread has a disproportionate influence on the performance.
In such applications, on X3D2 the slowest thread has a 3 times bigger cache on an X3D2 vs. X3D. That can make a lot of difference.
So there will be applications with no difference in performance, but also applications with a very large difference in performance, equal to the best performance differences shown by X3D vs. plain 9950X.
Can someone explain if the 3D Vcache are stacked on top of each other or side by side.
If they are stacked then why not 9800X3D2?
The 99xx chips have two CPU dies, and one cache die is on each CPU die.
The 3D V-Cache sits underneath only one of the CCDs. See https://en.wikipedia.org/wiki/Ryzen#Ryzen_9000.
That's what's different about this one. "Enter the Ryzen 9 9950X3D2 Dual Edition, a mouthful of a chip that includes 64MB of 3D V-Cache on both processor dies, without the hybrid arrangement that has defined the other chips up until now."
Did you forget which thread we are on?
Given that the dies still have L3 on them does this count as L4 or does the hardware treat it as a single pool of L3?
Would be neat to have an additional cache layer of ~1 GB of HBM on the package but I guess there's no way that happens in the consumer space any time soon.
Per compute die it functions as one 96M L3 with uniform latency. It is 4 cycles more latency than the configuration with smaller 32M L3. But there are two compute dies, each with their own L3. And like the 9950X coherency between these two L3 is maintained over global memory interconnect to the third (IO) die.
With the best silicon tech, in R&D, what would be the maxium static RAM(L1 cache) you could really slap to a 8 core CPU? (Zero DRAM).
I have a gigabyte of cache on my 9684x at home!
Can someone like... boot Windows 98 on these on a system with no ram?!
Conceptually - yes, easily.
But to do it literally - I'm not a low-level motherboard EE, but I'd bet you're looking at 5 to 7 figures (US $) of engineering work, to get around all the ways in which that would violate assumptions baked into the designs of the CPU, support chips, firmwares, etc.
Make a fake ram which offers write through guarantee and returns bus no matter what address is referenced. You could possibly short circuit any "is ram there" test if it just says yes for whatever size and stride got configured.
that is larger than the HDD of my first PC.
My first computer had 64KB of RAM. My first PC had 8MB of RAM.
It's disappointing that they had this for years but didn't release it until now.
I think it’s mostly that they had leftover cache.
This video made the argument that AMD released it to not give Intel a look-in: [AMD KILLED Intel's 290K Dreams w/ R9 9950X3D2](https://www.youtube.com/watch?v=u7SyrDPbKls)
Makes sense. RAM pricing surely has lead to a fall of AM5 high-end CPU purchases, might as well try to get some extra cash from those who still buy. Bin the remaining now non-X3D chips as something else.