DRYOS is an embedded real-time operating system developed by Canon for use in compact devices and employed in a wide range of company products such as digital cameras and digital video camcorders.
Source: Canon Inc.
“ OS Switch Since late 2007 Digic-based cameras are shipped using Canon's own Operating System...DryOS Porting
“DryOS Shell is available via UART Serial Connection with Camera. Start Shell On Camera Startup...DryOS Shell
“Event Shell is available on (almost?) all Cameras via UART connection. Look SD4000 for...Event Shell