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Old 10-19-2009, 06:28 PM   #1
Registered: Feb 2004
Location: Manorville, New York, USA
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KVM and DOS - cpu to 100%

I tried loading up FreeDos and MS-DOS 6.x as a kvm guest. The only problem was that in a resting state, running either dos jacked up the cpu to 100%. I'm still new to kvm, does anyone know if there was a setting that I missed that would prevent the cpu from jumping that much?
Has anyone else tried to put up dos in a virtual setting, just curious.

Old 10-20-2009, 03:49 AM   #2
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This is a common problem with early operating systems in virtual machines, because they idle by running a busy loop. So they appear to the virtual machine as if they are busy all the time.

There is no really satisfactory solution. There are idle programs that you can run (eg or POWER in DOS, FDAPM in FreeDOS, or cpuidle or cpucool for the Win95 series of operating systems). However, because DOS is a single tasking system, as soon as you start a program (such as an editor), it may go back to using 100% CPU.

The other thing you can do to alleviate the problem is to use nice to run the virtual machine at a lower priority; it doesn't stop it using 100% CPU, but at least it has less of an impact on other programs you are running independently of the virtual machine.

Another option is to run WinNT or Win2000 in the virtual machine, and run your DOS applications from a terminal. However, not all DOS apps will work, and it certainly smells like overkill!

Last edited by neonsignal; 10-20-2009 at 03:56 AM.
Old 10-20-2009, 11:27 AM   #3
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Thanks neonsignal
That's just the answer I was looking for. I'm going to look at the links you gave me, but I'll probably just try loading dos on an old laptop and leave it at that.
I have a client who is running a Marina Manager I wrote in Forth 25 years ago. Every few years he asks me to do some maintenance for him, and every few years I have to figure out where to run the program while working on it. The client runs the program on 386 computers, all my 386 boxes are long gone.

Thanks for your help.


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