Historical installation guidance lists an RZ56-sized 635 MB disk as the OpenVMS V6.2 minimum and recommends at least 1 GB. The current 5.1.0 evidence validates V6.2 storage at larger sizes but does not test the 635 MB boundary. Treat that value as a historical floor, verify the requirements of the exact installation kit and layered products, and allocate additional space for updates, paging, logs, and application data.