Subj : Interrupts
To   : David Noon
From : Lee Aroner
Date : Sun May 27 2001 03:18 am

 DN>> The OS/2 API is built on call gates and ring gates, not interrupts.

 LA>    And are not those gates accessed via an interrupt?

DN> No.

DN> Call gates are simply part of protected mode execution. 
  > They do not generate any interrupt; they simply fiddle some 
  > segment registers [and control registers and stack frame, 
  > if they are ring gates too] and then continue execution as 
  > per a normal CALL instruction.

DN> The use of an INT instruction in p-mode, as per PC-DOS/MS-
  > DOS/DR-DOS + DPMI (e.g. Win 3.x/9x/Me), NT and LINUX, is an 
  > alternative way to switch ring levels. In addition to 
  > branching to the address in the interrupt vector (addressed 
  > by the IDTR in p-mode) the INT instruction switches to ring 
  > 0. But this is wholly redundant in an OS that uses 
  > call/ring gates.

   My wrong. Thanks for taking the time to explain that. I had 
   simply assumed that OS/2 used the same invalid int trick to 
   switch rings as Win does.


DN> I guess that makes OS/2 a "Gates environment".

   AAAAAAAAAARRRRRRRRRGGGGGGGGGGGHHHHHHHHHH!!!!!!!!!!!



                                       LRA


 -- SPEED 2.01 #2720: "Give up integrity and the rest is a piece of cake." BG

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