David Hess (davidwhess.delete@this.gmail.com) on August 2, 2022 10:24 pm wrote:
> Doug S (foo.delete@this.bar.bar) on July 30, 2022 10:43 pm wrote:
> > David Hess (davidwhess.delete@this.gmail.com) on July 30, 2022 3:44 pm wrote:
> > > David Hess (davidwhess.delete@this.gmail.com) on July 29, 2022 8:59 pm wrote:
> > >
> > > Last night I remembered another computer system which could start up exactly where it
> > > left off after power loss; this was a feature of some systems which used core memory.
> > > It was a small step from relying on core memory for program and data storage, to including
> > > circuits to safely shut down and restart after power loss by saving CPU state.
> > >
> > > This could also have been done with a microprocessor and CMOS SRAM or even DRAM, but
> > > I do not remember any systems which did it that way. Someone must have though.
> >
> > This is before my time but in the core memory days booting was kind of a pain
> > in the ass, was it not? Even if you had the luxury of a hard drive you probably
> > had to either toggle in a bootloader or load it via paper tape.
> >
> > That was probably the main reason that was used, not necessarily because they wanted to pick up where
> > they left off - but if the PC, SP and registers were themselves stored in a type of core memory (or
> > there was a big capacitor or something allowing a split second for them to be saved to core memory)
> > then I guess theoretically it could simply pick up where it left off once power returns.
>
> Core memory was contemporaneous with SRAM, DRAM, ROM, PROM, UVEPROM, and floppy disk storage.
> The oldest systems I worked on booted a monitor from UVEPROM which then booted from floppy
> disk, but embedded systems ran directly from UVEPROM. It was the mini-computers which commonly
> had core memory but they also booted from floppy disk or UVEPROM. Any combination was possible
> in an embedded system. Toggling in a bootloader was optional by then.
>
> Low power CMOS SRAM suitable for battery backup did not exist yet though. It was sometimes
> done anyway with huge batteries to give only hours to days of backup time. One of my digitizing oscilloscopes was setup that way.
>
> For an embedded system running from ROM and/or core memory, there was plenty of time after detecting
> loss of power to save the processor state, which is still the case today for many embedded systems.
> Back then it might be no more complicated than subroutine entry and exit.