In the first stage, the existing system would be moved on top of a new kernel-based OS with built-in support for multitasking and protected memory. The existing libraries, like QuickDraw, would take too long to be rewritten for the new system and would not be converted to be reentrant. Instead, a single paravirtualized machine, the Blue Box, keeps applications and legacy code such as QuickDraw in a single memory block so they continue to run as they had in the past. Blue Box runs in a distinct Copland memory space, so crashing legacy applications or extensions within Blue Box cannot crash the entire machine.