Tests are performed prior to or during the boot operation to determine whether files are corrupted. This may indicate the presence of a virus. If a potential error is detected, boot is halted, allowing the user to boot from uncorrupted files. In another embodiment, an uniquely formatted floppy diskette...http://www.google.com.tw/patents/US5475839?utm_source=gb-gplus-share專利 US5475839 - Method and structure for securing access to a computer system
