
Physical Order is the layout of data storage in physical memory. For vision models, usually we talk about NCHW, NHWC. These are the descriptions of physical memory layout, also referred as Channels First and Channels Last respectively.
Logical Order is a convention on how to describe tensor shape and stride. In PyTorch, this convention is NCHW. No matter what the physical order is, tensor shape and stride will always be depicted in the order of NCHW.

Fig-1 is the physical memory layout of a tensor with shape of [1, 3, 4, 4] on both Channels First and Channels Last memory format (channels denoted as R, G, B respectively):




Fig-1 Physical memory layout of Channels First and Channels Last

Memory Formats Propagation