AMD Smart Access Memory May Only Work on Zen 3 CPUs

[Tsing]

Image: AMD



The landing page for AMD’s Smart Access Memory feature deliberately notes that users will require a 500 Series motherboard and Ryzen 5000 Series processor. While some enthusiasts have claimed that this is some kind of marketing ploy to get more Zen 3 CPUs off the shelves, we are seeing reports on social media that suggest the restriction is legitimate and stems from hardware limitations of older architectures.



According to a post on the CapFrameX account (via...

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[ThreeDee]

...well ain't that just a kick in the pants ..

 

[Brian_B]

Well, disappointing as it may be - it’s not like you went out and bought that 1700X back in 2017 just for it to work with SAM.

AMD hasn’t taken anything away from the older CPUs, nor have they failed to deliver anything they had promised — you got what you paid for.

 

[Eduardo_Domingot]

Oh come on AMD, prove everyone wrong here...

 

[Brian_B]

From what I have heard, the older AMD CPUs don't have the native instruction for SAM - they can do Resizable BAR, but it's via a compound series of instructions, and once you do that, you lose the speed benefit.

TechPowerUp notes that the new Ryzen 5000 CPUs are the only AMD series to integrate the PCIe physical layer feature called full-rate _pdep_u32/64,which allows processors to see the GPU’s entire video memory as a single addressable block instead of separate 256 MB apertures. It is true that Zen2 CPUs use the same IO die and PCIe controller as Zen3, but AMD SAM is actually controlled through a new ISA CPU instruction set. These specific instructions are only emulated in microcode using other similar instructions in the Zen2 and older cores, and this makes everything predating the new Ryzen 5000 essentially too slow to benefit from the performance uplift offered by SAM.

Here is why AMD might never include Smart Access Memory support on Ryzen 3000 and older models, while 6-year-old Intel CPUs can still benefit from this feature

It is quite ironic how AMD's Smart Access Memory (aka Resizable BAR) could help Intel and Nvidia regain some lost market shares. AMD offered to help its competitors with the Resizable BAR feature, yet Team Red may have hit a stone wall with the SAM support for Ryzen 3000 and older Zen-based...

www.notebookcheck.net

 

[Eduardo_Domingot]

From what I have heard, the older AMD CPUs don't have the native instruction for SAM - they can do Resizable BAR, but it's via a compound series of instructions, and once you do that, you lose the speed benefit.

Here is why AMD might never include Smart Access Memory support on Ryzen 3000 and older models, while 6-year-old Intel CPUs can still benefit from this feature

It is quite ironic how AMD's Smart Access Memory (aka Resizable BAR) could help Intel and Nvidia regain some lost market shares. AMD offered to help its competitors with the Resizable BAR feature, yet Team Red may have hit a stone wall with the SAM support for Ryzen 3000 and older Zen-based...

www.notebookcheck.net

Thanks for that info, I have not seen this at all, time for some reading to see what I missed.

 

[Elf_Boy]

Cant microcode be patched?