4 ms·

Is it really unified memory? AMD Strix Halo is "unified" but you still have to allocate memory separately for cpu vs gpu. Apple Silicon is true unified memory.

joe_mamba 4mo ago
>AMD Strix Halo is "unified" but you still have to allocate memory separately for cpu vs gpu. IIRC that's due to maintain BIOS and Windows (+games & apps) backwards compatibility, but memory access speeds are the same.
ankurdhama 4mo ago
It is unified in the sense that the OS can dynamically assign memory to CPU and GPU. Apple silicon is not a alien tech that other silicon vendors cannot implement.
ApatheticCosmos 4mo ago
Strix halo is unified memory. The memory allocation set in BIOS is overridden by the operating system if it has the capability.
eigenspace 4mo ago
That's a software question, not a hardware question. Some software assumes pre-defined set-aside pools of memory reserved for video purposes, but the chip does actually have access to the whole pool.
fc417fc802 4mo ago
> you still have to allocate memory separately for cpu vs gpu That's an API issue not a hardware issue. Regardless, I believe the major APIs permit seamlessly sharing pointers at this point? (I have no experience doing that though.)
flakiness 4mo ago
My understanding is that this is the limitation from Windows not from AMD SoC. There are several internet resources to "enable unified memory support" on linux eg [1]. As a side note, qualcomm chip set on Android has been doing this for years (like Apple) so it's not super unique thing. It's more like there was no need before. [1] https://www.jeffgeerling.com/blog/2025/increasing-vram-allocation-on-amd-ai-apus-under-linux/ https://www.jeffgeerling.com/blog/2025/increasing-vram-alloc...
- kimixa 4mo ago
  Even then the "reserved" section is a carve out guaranteed chunk to allow stuff that might need contiguous physical memory (display scan out buffers and page tables, for example) and similar. The GPU can still happily use all the rest of the memory for other use cases - which tend to be the bulk of allocations anyway. Though there might be performance implications - for example "moving" buffer ownership to the GPU would need to evict CPU caches, and often 4k pages and tlb lookups can be a pretty inefficient situation for GPU-style accesses. That's been pretty standard for any SoC for decades. And "differences" to apple's SoC are more implementation details.
SwtCyber 4mo ago
For local models, the useful part is not just having 128GB attached to the package. It is whether the GPU can practically use that memory without the usual VRAM-style constraints
Keyframe 4mo ago
yes, but more due to OS limitations than hardware. You can use their GTT which is then _true_ UMA where GPU can grab whatever it wants from the memory pool. This isn't the first time we have UMA on the PC, btw. When SGI did their PC workstations, their 320 and 540 PC workstations had what they called Cobalt graphics chipset and crossbar with their IVC architecture. They bypassed AGP at the time completely. It was quite unique to see strict UMA on a PC. Haven't seen it since until these new systems we're seeing now on PCs and Mac.
glitchc 4mo ago
Memory bandwidth is what matters, unified or otherwise. Discrete GPUs don't have unified memory either.

joe_mamba 4mo ago

>AMD Strix Halo is "unified" but you still have to allocate memory separately for cpu vs gpu. IIRC that's due to maintain BIOS and Windows (+games & apps) backwards compatibility, but memory access speeds are the same.

ankurdhama 4mo ago

It is unified in the sense that the OS can dynamically assign memory to CPU and GPU. Apple silicon is not a alien tech that other silicon vendors cannot implement.

ApatheticCosmos 4mo ago

Strix halo is unified memory. The memory allocation set in BIOS is overridden by the operating system if it has the capability.

eigenspace 4mo ago

That's a software question, not a hardware question. Some software assumes pre-defined set-aside pools of memory reserved for video purposes, but the chip does actually have access to the whole pool.

fc417fc802 4mo ago

> you still have to allocate memory separately for cpu vs gpu That's an API issue not a hardware issue. Regardless, I believe the major APIs permit seamlessly sharing pointers at this point? (I have no experience doing that though.)

flakiness 4mo ago

My understanding is that this is the limitation from Windows not from AMD SoC. There are several internet resources to "enable unified memory support" on linux eg [1]. As a side note, qualcomm chip set on Android has been doing this for years (like Apple) so it's not super unique thing. It's more like there was no need before. [1] https://www.jeffgeerling.com/blog/2025/increasing-vram-allocation-on-amd-ai-apus-under-linux/ https://www.jeffgeerling.com/blog/2025/increasing-vram-alloc...

kimixa 4mo ago
Even then the "reserved" section is a carve out guaranteed chunk to allow stuff that might need contiguous physical memory (display scan out buffers and page tables, for example) and similar. The GPU can still happily use all the rest of the memory for other use cases - which tend to be the bulk of allocations anyway. Though there might be performance implications - for example "moving" buffer ownership to the GPU would need to evict CPU caches, and often 4k pages and tlb lookups can be a pretty inefficient situation for GPU-style accesses. That's been pretty standard for any SoC for decades. And "differences" to apple's SoC are more implementation details.

SwtCyber 4mo ago

For local models, the useful part is not just having 128GB attached to the package. It is whether the GPU can practically use that memory without the usual VRAM-style constraints

Keyframe 4mo ago

yes, but more due to OS limitations than hardware. You can use their GTT which is then _true_ UMA where GPU can grab whatever it wants from the memory pool. This isn't the first time we have UMA on the PC, btw. When SGI did their PC workstations, their 320 and 540 PC workstations had what they called Cobalt graphics chipset and crossbar with their IVC architecture. They bypassed AGP at the time completely. It was quite unique to see strict UMA on a PC. Haven't seen it since until these new systems we're seeing now on PCs and Mac.

glitchc 4mo ago

Memory bandwidth is what matters, unified or otherwise. Discrete GPUs don't have unified memory either.