4 GB RAM under FreeDOS

Here are some test results which may be of interest to anyone with over 2 GB of RAM wanting to run protected mode programs. I have a P4 with 4 GB RAM which came with Windows XP (home) pre-loaded. The Windows DPMI server will not allow an application to access more than about 1.75 GB of the 4 GB installed. My task has been to find a configuration to access as much as possible of the RAM (the system requires about 750 MB or so, ).

 

With FD HIMEM.EXE and FD EMM386.EXE: CWSDPMI won't load, but 3.24 GB is seen in real mode extended memory manager. This was the first set-up I tried and I repeat the memory dump:-

 

Memory Type           Total      -      Used     =     Free (largest)
-------------------            -------            ---------           --------------------
Conventional             640K            74.2K            565K
Upper (XMS)                                                     64.0K
Extended (INT15)      3.24G                                0
Extended (XMS16)                                             63.9M
Extended (XMS32)                                             3.21G
Expanded (EMS)       32.1M          64K               32.0M

With FD HIMEM.EXE only:3.24 GB of XMS32 RAM shown in real mode, CWSDPMI loads OK and sees just under 2 GB but DPMIONE sees all 3.24 GB This is the setup I am using now.

With No HIMEM at all: Real Mode: Conventioal 640 K, Extended (INT15) 3.24 GB
                                       Prot. Mode: DPMIONE won't load, CWSDPMI sees 2146320384 bytes

 

It seems that the real mode memory manager works fine, but for protected mode where DPMI is required, CWSDPMI, like the Windows DPMI server, cannot serve more than 2 GB of RAM, but DPMIONE can, so this would seem to be the best choice for a DPMI server if you have more than 2 GB of physical RAM.

 

I hope this of interest. Best wishes,

 

Roberto Waldteufel