https://docs.unity3d.com/Manual/SL-ShaderCompileTargets.html

#param target 2.0

不同版本支持的特性如下：

Supported #pragma target names

Here is the list of shader models supported, with roughly increasing set of capabilities (and in some cases higher platform/GPU requirements):

pragma target 2.0

Works on all platforms supported by Unity. DX9 shader model 2.0.
Limited amount of arithmetic & texture instructions; 8 interpolators; no vertex texture sampling; no derivatives in fragment shaders; no explicit LOD texture sampling.

pragma target 2.5 (default)

Almost the same as 3.0 target (see below), except still only has 8 interpolators, and does not have explicit LOD texture sampling.
Compiles into SM3.0 on DX9, and DX11 feature level 9.3 on Windows Phone.

pragma target 3.0

DX9 shader model 3.0: derivative instructions, texture LOD sampling, 10 interpolators, more math/texture instructions allowed.
Not supported on DX11 feature level 9.x GPUs (e.g. most Windows Phone devices).
Might not be fully supported by some OpenGL ES 2.0 devices, depending on driver extensions present and features used.

pragma target 3.5 (or es3.0)

OpenGL ES 3.0 capabilities (DX10 SM4.0 on D3D platforms, just without geometry shaders).
Not supported on DX9, DX11 9.x (WinPhone), OpenGL ES 2.0.
Supported on DX11+, OpenGL 3.2+, OpenGL ES 3+, Metal, Vulkan, PS4/XB1 consoles.
Native integer operations in shaders, texture arrays, etc.

pragma target 4.0

DX11 shader model 4.0.
Not supported on DX9, DX11 9.x (WinPhone), OpenGL ES 2.0/3.0/3.1, Metal.
Supported on DX11+, OpenGL 3.2+, OpenGL ES 3.1+AEP, Vulkan, PS4/XB1 consoles.
Has geometry shaders and everything that es3.0 target has.

pragma target 4.5 (or es3.1)

OpenGL ES 3.1 capabilities (DX11 SM5.0 on D3D platforms, just without tessellation shaders).
Not supported on DX9, DX11 before SM5.0, OpenGL before 4.3 (i.e. Mac), OpenGL ES 2.0/3.0.
Supported on DX11+ SM5.0, OpenGL 4.3+, OpenGL ES 3.1, Metal, Vulkan, PS4/XB1 consoles.
Has compute shaders, random access texture writes, atomics etc. No geometry or tessellation shaders.

pragma target 4.6 (or gl4.1)

OpenGL 4.1 capabilities (DX11 SM5.0 on D3D platforms, just without compute shaders). This is basically the highest OpenGL level supported by Macs.
Not supported on DX9, DX11 before SM5.0, OpenGL before 4.1, OpenGL ES 2.0/3.0/3.1, Metal.
Supported on DX11+ SM5.0, OpenGL 4.1+, OpenGL ES 3.1+AEP, PS4/XB1 consoles.

pragma target 5.0

DX11 shader model 5.0.
Not supported on DX9, DX11 before SM5.0, OpenGL before 4.3 (i.e. Mac), OpenGL ES 2.0/3.0/3.1, Metal.
Supported on DX11+ SM5.0, OpenGL 4.3+, OpenGL ES 3.1+AEP, Vulkan, PS4/XB1 consoles.
Note that all OpenGL-like platforms (including mobile) are treated as “capable of shader model 3.0”. WP8/WinRT platforms (DX11 feature level 9.x) are treated as only capable of shader model 2.5.