4 ms·

I'm really surprised that the DOS extenders weren't the first solution to appear…

• mwcampbell 9y ago
  If I understand the article correctly, DOS extenders weren't feasible until the 386, because the 286 couldn't switch out of protected mode and back to real mode except by doing a full reset.
  • WalterBright 9y ago
    There were effective 286 DOS Extenders. Zortech included the Rational Systems 286 DOS Extender with the Zortech C++ compiler.
    • bni 9y ago
      After reading the article, I am really curious how these could work.
      • cardiffspaceman 9y ago
        We're talking protected mode. The segment register would be an index into a table of segments of memory and the segments would be implemented in your RAM, and all of them would be accessible "at once" modulo the fact that there were only a few segment registers. The DOS extender could hack DOS so that you could in some fashion call DOS through "INT 21h" and it would do something (emulation, call through glue code into real mode etc). The call might require a transition into and out of real mode, which would not be cheap. Sometimes the only way to call DOS was to use "low" memory that was directly accessible from real mode, and you'd need to use special routines instead of malloc/free to manage that memory. You'd still have to call DOS through a hack but the memory arguments of the call would not need to be rearranged within the extender.