This document introduces HDF5 as a new data format that addresses limitations of SEGY, such as only allowing sequential access. HDF5 allows random access, extended metadata, and scales better to large datasets. It describes how to create and read HDF5 files in Claritas using new modules like SEISWRITE and SEISREAD that replace DISCWRITE and DISCREAD. Selections, repeats, and reading multiple files work similarly to existing Claritas tools but with improved flexibility and performance.