ComputeShader programs often need arbitrary data to be read & written into memory buffers.
ComputeBuffer class is exactly for that - you can create & fill them from script code,
and use them in compute shaders or regular shaders.
Compute buffers are always supported in compute shaders. Compute shader support can be queried runtime using SystemInfo.supportsComputeShaders. See the Compute Shaders Manual page for more information about platforms supporting compute shaders. In regular graphics shaders the compute buffer support requires minimum shader model 4.5.
For a ComputeBuffer that uses a counter, Metal and Vulkan platforms don't have native counters and use separate small buffers that act as counters internally. These small buffers are bound separately from the ComputeBuffer and count towards the limit of possible buffers bound (31 for Metal, based on the device for Vulkan).
On the shader side, ComputeBuffers with default ComputeBufferType map to StructuredBuffer<T> and RWStructuredBuffer<T> in HLSL.
Additional resources: ComputeShader class, Shader.SetGlobalBuffer, Material.SetBuffer, Compute Shaders overview.