2 ms·

After reading the article, I am really curious how these could work.

• cardiffspaceman 10y 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.