Virtual 86 Mode

[VoidLogic]

I know what protected and real mode are, but what is V86 mode? What is the memory arch. etc. Info Plz

-VoidLogic

[mikeleany]

Virtual 8086 (V86) mode just allows programs to run in a protected mode environment, but think that they are in real mode. From the programs perspective, the architecture is exactly the same as real mode, well, almost. That way you don't have to keep switching back and forth. For example, DOS programs running in Windows are running in V86 mode. The IA-32 Manual Vol 3 explains it (http://developer.intel.com/design/Pentium4/manuals/) in Chapter 16, but it's a little hard to read. Is there anything specific you wanted to know about it?

[VoidLogic]

In V86 moded can i set the progams to have more than the 1 mb of conv. memory?
Do they need to use the real moded methods of getting to XMS?
Also, If I diable the A20 line and go back into real mode (unreal mode) can MS-DOS or PC-DOS use the new > 4 GB as conventional memory.
Thanks

VoidLogic

[mikeleany]

You can use 1MB + 64KB without any problem. I don't know about using memory beyond that, but it looks like it is usable. If you disable the A20 line you can't use odd Megabytes (1M-2M, 3M-4M, ...) at all. But if you left it enabled and went to unreal mode, I don't think MS-DOS would do anything with the memory above 1MB + 64KB.

[VoidLogic]

In unreal mode how could i use this memory >1088k? My OS runs ontop of DOS like 3.1 did. Its more of a shell in fact, but i need to get the memory systems full potenial. My OS uses recursive software to mimit multitaking, so my OS is generally very stable, machine inpedendent, but not real fast.
Thanks again

VoidLogic