[syslinux] memdisk: DOS as a PreOS

Gordon Dey gordon.dey at fidus.ca
Mon Jun 28 11:01:36 PDT 2004

On June 28, 2004 12:01 pm, Matthew Moffitt wrote:
> This is something I would be interested to see as well.  The
> 3com/Lanworks environment we used to use had a pboot.exe utility that

The basic skeleton of this is in H.Peter Anvin's memdisk already: go read 
sector 1 of device 80h (to, say, 7c00h) and jump to it. Check out the code 
near the end of setup.c, you'll see what I mean, it's what I started with. 
One could probably use the com32 stuff to create the utility too, if using 
DOS-or-alike. But I'm getting well out of my comfort area here :-)

> there by any more flexibility working from another OS in the floppy

One would need a way "out" of whatever was running on the virtual disk. Most 
OSs assume that they are the end of the line: there is *no* way back. 
By-and-large, this is a good assumption with a number of useful byproducts, 
like never having to worry about what the devices were initialised to and 
how, and what the memory allocation and stack used to look like, before 
starting. For example, memdisk stays resident by decrementing the bios' idea 
of how much space it has.

In my case, I'm trying to be floppy OS agnostic, but the underlying memdisk 
hooks have to work in order for the virtual floppy to stay visible. I don't 
want to write/use per OS specific helper functions if I can.

73, Gord.

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