RTM kernels are used to realize the forward and backward wave propagation paths. They are constructed by connecting multiple forward (see: Forward streaming module) and / or backward (see: Backward streaming module) modules and data mover modules together. The RTM applications in this library is realized on Xilinx Alveo U280 card, which has 2 HBM stacks and 2 DDR device modules attached to the FPGA. Each HBM stack stores 4GB data, 8GB storage in total. Each DDR device stores 16GB data, 32GB storage in total. The RTM kernels use HBM devices to store the wavefield data, image data and velocity model data. The boundary values and other parameters including the source and receiver data are stored in DDR devices.