Editing Openai/69676758-d944-8003-a3d4-835e33b4e372 (section)

=== Assistant: They are formal driver models and kernel interfaces defined by the operating system. ===
They are formal driver models and kernel interfaces defined by the operating system. GPU vendors must implement them to plug their hardware into the OS.

Below is a precise breakdown, without hand-waving.

==== ### ====

This is the core interface.

It defines:
* How the GPU is scheduled and preempted
* Video memory management
* Context isolation between processes
* Display modesetting and scanout ownership
* Power management
* Multi-GPU behavior

GPU vendors provide:
* A kernel-mode driver (dxgkrnl interface)
* One or more user-mode drivers: - Direct3D (D3D11/12) - Vulkan - OpenGL

Windows itself:
* Owns the desktop compositor (DWM)
* Enforces security and stability rules
* Does not know GPU internals

==== Linux splits graphics into several interfaces. ====

===== Kernel-space interface that defines: =====
* GPU memory objects (GEM/TTM)
* Command submission
* Scheduling and fences
* Display control (CRTCs, planes, connectors)
* Atomic modesetting

Vendors implement:
* Kernel drivers (amdgpu, i915, nouveau, nvidia-drm)

===== These sit on top of DRM: =====
* Vulkan (via vendor ICD)
* OpenGL (usually via Mesa)
* EGL / GBM (buffer management and window system glue)

The window system (Wayland/X11) never touches the hardware directly.

==== ### ====

Apple tightly controls this stack.
* GPU drivers are written by Apple (sometimes with vendor cooperation)
* Metal is the only first-class graphics API
* Display management is integrated into the OS

Third-party low-level access does not exist.

==== They all define: ====
* How commands enter the GPU
* How memory is shared and isolated
* How display ownership works
* How preemption and fault handling occur

They explicitly hide:
* Command encodings
* Display PHY details (DP/HDMI)
* PCIe transactions
* Scanout timing internals

==== Your code path stops here: ====

<syntaxhighlight>Your code
  → Vulkan / DirectX
    → User-mode driver
      → Kernel driver (WDDM / DRM)
        → Hardware

</syntaxhighlight>

You never cross the API boundary.

==== OS interfaces are formal contracts between the OS and GPU vendors. ====
They are not optional, and they are not bypassable in normal applications.

If you want, I can map a single Vulkan call all the way down to which OS interface handles it, step by step.