32 Bit DOS Protected Mode Application

[Gunther]

Andreas,

That depends what you want to achieve.

a Beowulf cluster with FreeDOS.

Accessing memory beyond the 4 GB barrier requires some low-level work for a DOS app, since there exists no "unreal"-mode trick to do that.

that's surprising at all. I thought this is only possible in Long Mode. Are there any examples of this?

[_japheth]

a Beowulf cluster with FreeDOS.

I see.

that's surprising at all. I thought this is only possible in Long Mode. Are there any examples of this?

Memory beyond 4 GB can be accessed by using special paging types:

1. PSE paging. I used it in https://github.com/Baron-von-Riedesel/HimemSX to create a special XMS host that can access up to 1 TB.
It's also used by CWSDPMI v6/7 to backup virtual memory up to 4 GB.


2. PAE paging. That's more powerful ( and the type of paging also used in long mode). For a simple usage in DOS see https://github.com/Baron-von-Riedesel/DOS32pae

[Gunther]

Andreas,

thank you for your advice.

Memory beyond 4 GB can be accessed by using special paging types:

1. PSE paging. I used it in https://github.com/Baron-von-Riedesel/HimemSX to create a special XMS host that can access up to 1 TB.
It's also used by CWSDPMI v6/7 to backup virtual memory up to 4 GB.

1 TB for a DOS application sounds very impressive. If I understand correctly, HimemSX can be included under FreeDOS. That would already be a viable alternative for me. This should then even work in a virtual machine.

2. PAE paging. That's more powerful ( and the type of paging also used in long mode). For a simple usage in DOS see https://github.com/Baron-von-Riedesel/DOS32pae

That would be almost Long Mode. I'll have a look at that as well.

[Gunther]

Andreas,

I found this on FreeDOS. It's JEMM version 5.79d.

In the XMS v3.5 API you've written:

  In V86 mode, the XMM's 'move extended memory' function (AH=0Bh) will need the
  help of the Expanded Memory Manager (EMM), since privileged code has to be
  executed. The only EMMs that currently support accessing memory beyond 4 GB
  are Jemm386/JemmEx v5.80+. Their Int 15h API has been exhanced as well.

Is there a binary package available for download of version 5.80?

[_japheth]

Is there a binary package available for download of version 5.80?

Yes, https://github.com/Baron-von-Riedesel/Jemm/releases/download/v5.80/JemmB_v580.zip

[Gunther]

Thank you.