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AMD's Ryzen 9 9950X3D2 Dual Edition crams 208MB of cache into a single chip

arstechnica.com

11–20 of 179 posts

Re: AMD's Ryzen 9 9950X3D2 Dual Edition crams 208MB of cache into a single chip

#11
post #3

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.

Re: AMD's Ryzen 9 9950X3D2 Dual Edition crams 208MB of cache into a single chip

#12
post #4

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.

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.

Re: AMD's Ryzen 9 9950X3D2 Dual Edition crams 208MB of cache into a single chip

#13
post #4

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.

I wonder how much faster dos would boot, especially with floppy seek times...

Re: AMD's Ryzen 9 9950X3D2 Dual Edition crams 208MB of cache into a single chip

#14
post #4

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.

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.

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

Re: AMD's Ryzen 9 9950X3D2 Dual Edition crams 208MB of cache into a single chip

#15
post #13
post #4

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.

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".

Re: AMD's Ryzen 9 9950X3D2 Dual Edition crams 208MB of cache into a single chip

#16

Earlier quoted context omitted.

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.

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

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?

Re: AMD's Ryzen 9 9950X3D2 Dual Edition crams 208MB of cache into a single chip

#18

Earlier quoted context omitted.

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.

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

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.

Re: AMD's Ryzen 9 9950X3D2 Dual Edition crams 208MB of cache into a single chip

#19
post #10
post #4

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.

In my case it began with 16K (yes, 16 1024 bytes) and 90K (yes, 90 1024 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).
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