The 6ES7151-7FA20-0AB0: Onboard memory totals 128 kB for program and data, with 244 bytes each of process input and output image. That memory budget fits a medium-sized station with a few dozen I/O and some interlocking logic; for larger applications watch the program size limit.
Physical footprint: 60 mm wide (35 mm for DP master variant), 75 mm deep, 119.5 mm high. Backup time 6 weeks at 40 °C ambient, typical. Integrated functions: forcing of I/O is supported (useful for commissioning), single-step and breakpoint debugging are available, and equidistant DP cycles are configurable down to 1 ms. The module can also serve as an OPC UA server for data routing.