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Using Multiple CPU Cores in DOS? (Miscellaneous)

posted by tom(R) Homepage, Germany, 20.09.2011, 20:17
(edited by tom on 21.09.2011, 12:43)

> > A20 will be enabled by each INT 21, (usually DOS lives in memory above
> 1M),
> > and left enabled.
> > A20 is disabled when when a program is started.
> > as most programs call int 21 sooner or later, A20 is reenabled again by
> int
> > 21, and left enabled.
> >
> > therefore it's fast, almost all time.
> I can see where somebody may want this as an option, but it definitely
> shouldn't be the default.
it IS the default, and it costs NOTHING.

A20 is enabled ALL THE TIME except a few microseconds..

btw: in protected mode, A20 switching is implemented by leaving A20 enabled all the time, but on Enable/DisableA20 the page tables are modified so that
the 'visible' memory at ffff:10.. ffff:ffff is either physical memory 000000 or 00100000

> This is potentially penalizing
> (performance-wise) the VAST majority of programs that work like they're
> supposed to, and catering to a few rare, buggy programs that have another
> option (LOADFIX) available to them anyway.
btw: this is penalizing the poor *users*, not the programs. the programs don't care


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