An electronic printing system with plural hard disks for storing system files in which upgraded software together with software identification data is written to a first of the disks, the system booted from the first disk, and the upgraded software thereafter migrated from the first disks to the other...http://www.google.de/patents/US5257377?utm_source=gb-gplus-sharePatent US5257377 - Process for automatically migrating a subset of updated files from the boot disk to the replicated disks
