You have inspired more questions about incremental saves: speed was an obvious issue with personal computers, but was it implemented on any minis or mainframes?

You have inspired more questions about incremental saves: speed was an obvious issue with personal computers, but was it implemented on any minis or mainframes? These were multiuser systems (i.e. multitasking), so they could do background disk I/O. Also, would it be a possibility on some personal computers? For example: 8-bit Commodore computers had their own CPU and could operate indepedently from the computer, while the 6809 was famous for being sophisticated enough to support multitasking (e.g. OS-9). Even less sophistcated machines could do I/O in the background if the disk controller signalled the completion of a read/write operation via interrupts. I'm asking because it is also possible that such features weren't implemented because the weren't thought of or because the defied contemporary expectations.