copy tftp://<server-ip>/c3640-jk9s-mz.124-16.bin flash: configure terminal boot system flash:c3640-jk9s-mz.124-16.bin write memory reload While c3640-jk9s-mz.124-16.bin is a stable, feature-rich IOS release for the Cisco 3640, it is obsolete for modern secure networking. Its primary value today is in educational emulation and legacy lab scenarios. Do not download from unauthorized sources —obtain it through a Cisco account with an active contract, or use legal emulator images provided with platforms like Cisco Modeling Labs (CML).