Not very useful these days, but yes, some areas of the 640-1MB range
were indeed usable for dos ram. One particular was if you had a
monochrome monitor, you could allocate the other portion of ram that
color monitors used. I don't recall how much that added, but then there
was certain hard disk controllers that didn't use particular regions of
memory, and those too could have their unused portions mapped into dos
memory. I can't remember the name of the program to run to find ram
regions usable by dos, but at one point, I know I was able to get 704K
free for dos applications, and that was before loading anything high.
I do think there were some memory managers that could load parts of dos
high, even on 8086 machines, but again, no memory of what they were
called. I never used one on a regular basis, only to test it out, and
while it worked well enough, I wasn't ram starved, so I didn't worry
about it.
At one point, I had an intel above board which could remap extended
memory into lower dos ram, allowing you to swap programs in/out, which
would (sorta) allow more than 640K in dos, but you had to disable or
remove any physical ram above 128K so it could work to it's fullest
capability. I didn't do that, but I did allow it to map some portions
of extended memory into my dos ram to allow me some additional ems ram
which some dos apps could use, even not on a 386 machine.
That's about the extent of my experience with dos memory hacks.
On 7/11/2025 10:18 PM, Liam Proven via Freedos-user wrote:
On Fri, 11 Jul 2025 at 16:06, Eric Auer via Freedos-user
<freedos-user@lists.sourceforge.net> wrote:
but on older
CPU, it can easily happen that your mainboard can
support RAM which actually is in UMB areas.
I was an expert in DOS memory optimisation 35 years ago. This was
_extremely_ rare and either needed very specific hardware or software.
I stand by what I said: so rare as to effectively be impossible to do
in the 21st century when both the hardware and the software are very
rare
How about EDR-DOS? :-)
EDR-DOS is the kernel of SvarDOS. On its own it's just a kernel and little use.
And it's the kernel from DR-DOS 7.01 with many enhancements. Built for
a 486 with memory management. Not a good choice for a '186 or an
emulator.
I meant what I said, I stand by it, and it's based on coming up on 40
years of specialist expert knowledge.
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