Subj : Interrupts
To   : Lee Aroner
From : David Noon
Date : Sat May 26 2001 02:10 am

Hi Lee,

Replying to a message of Lee Aroner to David Noon:

 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?

No.

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.

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.

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

Regards

Dave
<Team PL/I>

--- FleetStreet 1.25.1
 * Origin: My other computer is an IBM S/390 (2:257/609.5)

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