Unlike overlays, however, chain loading replaces the currently executing program in its entirety.
The common data area comprises the process' environment variables, which are preserved across the system call.
The new kernel boots as if it were started from power up and no running processes are preserved.
On BBC BASIC, for example, only a specific subset of all variables are preserved across a CHAIN.
[3] OS/360 and successors use the XCTL (for "transfer control") macro for chain loading.