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wfjm.w11/doc/w11a_diff_70_red_stack_abort.md

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Known differences between w11a and KB11-C (11/70)

A 'red stack violation' loses PSW, a 0 is pushed onto the stack

The 11/70, together with the 11/45, has the most elaborate stack protection system of all PDP-11 models. A stack push via kernel stack is aborted when the stack pointer is in the 'red zone' 16 words below the stack limit. An emergency stack is set up, SP is set to 4, and PSW and PC are stored.

The w11a loses the PSW, a 0 is pushed.

'red stack aborts' are never recovered, all OS treat them as fatal errors. This difference is therefore considered an acceptable implementation difference.