A system that may optionally be partitioned into multiple domains is disclosed. Each domain is capable of independently powering on, executing a firmware program, and loading an operating system, including a legacy operating system, as well as running an application program that is distinct from programs running on another domain. Interrupts, including boot interrupts, reset handlers, and inter-chassis communications are initialized differently, depending on whether the system is to be partitioned or not. The cost of redundant hardware and/or firmware is substantially avoided, yet the system fully supports multiple domains.