Re: Is it possible to address more than 1MB in real-mode

H. Peter Anvin wrote:
Dirk Wolfgang Glomp wrote:

The problem is that if any interrupt handler ever goes in the PM, it will destroy unreal mode on return (there is, unfortunately, no sane way to read out the segment limits so they can be restored.) So you're playing a gamble with the underlying platform.

I didn´t know any normal DOS-IRQ that goes to PM, so only memmorymanager do
that?


You don't know what the BIOS does behind the back of either DOS or anything else. In particular, if the hardware requires access to high memory (as some disk and network controllers do these days), you have to go to PM.

I've been running AMI BIOS under a VT hypervisor lately (basically, booting an OS with int 19h using native I/O and virtualized memory), and it does use unreal mode (apparently, for some local APIC stuff, don't ask me why, I have no idea). It also does that if you use int 13h. Interrupt handlers do not go to PM, though, at least not the disk I/O ones.

By the way, emulating unreal mode with Intel's sucky VT is a special kind of fun.

.