Re: [Freedos-user] FreeDOS Memory

[Eric A. <e....@jp...>]

Hi Bernd, everybody,

let me add some more comments to this interesting DOS
thread and wish everybody a happy 2012 as well... :-)

>> 1. Would like to ask how much memory does FreeDOS support, e.g. 4 GiB?

If you have 4 GB or more, many mainboards will map your
graphics card RAM etc to the end of the first 4 GB, so
you only see e.g. 3.5 GB RAM when looking at the first
4 GB. Also, almost no DOS software looks beyond this 32
bit limit (another mail mentions an DOS/32A PAE update)
so if you have 12 GB, DOS apps still only see 3.5 GB.

On the other hand, many old Windows versions crashed if
you had more than, say, 256 MB (0.25 GB) of RAM unless
you tweaked some things. DOS does NOT have any problem.

However, some ANCIENT apps might crash, some already if
you have only 32 MB (!) or more. DOS memory drivers such
as HIMEMX have configuration options to make only a bit
of your memory visible to solve that sort of problem :-)

In general, 32 bit DOS apps will easily use many MB or
even a GB or more if you have it. Whether you have any
apps that NEED so much memory - I doubt it. People tend
to use memory for huge RAMDISKs or huge disk caches, so
the memory does not stay empty and bored... ;-)

>> 2. Does it faces 640 KiB limitation as MS-DOS, e.g. Do I have to "load
>> high" drivers to save on conventional memory?

This is more a problem of DOS apps than of DOS as the
operating system. You can load drivers, kernel and so
on into UMB and HMA to have more of the DOS 640k free
but on the other hand, 32 bit apps using DOS extenders
will use XMS (or EMS or other) memory anyway and you
have PLENTY of that so it does not matter how much of
your DOS 640k are free for those.

>> 3. Does it support usage of a swap file/partition?

DOS itself neither needs nor supports that, but again
for 32 bit apps, the DOS extender MAY support a swap
file, depending on the extender. For example CWSDPMI,
DOS32A and DOS4GW are DOS extenders: They help 32 bit
apps to interact with the 16 bit standard interfaces
of all brands of DOS and they help the apps to manage
megabytes or gigabytes of memory and sometimes swap.

Regards, Eric



PS: The FreeDOS spin-of FD32 is a DOS with a built-in
DOS extender, which is somewhat exotic but slightly
faster than classic DOS with separate DOS extenders.

PPS: JEMMEX is an EMM386 with a built-in HIMEM, which
is a bit exotic but smaller/faster than HIMEM+EMM386.