Tech Flashback: Microsoft MS-DOS Version 4.01

It’s been an extremely busy week, and I haven’t had much of a chance to do anything blog-related at all. Instead, I’m often left staring at piles of stuff I’ve meant to make a mention of on the blog, but haven’t gotten around to it yet.

As part of the large load of stuff which was salvaged for me by my friend at uni, was this pair of OEM Microsoft MS-DOS Version 4.01 5.25″ DS/DD 360kB install floppies. Unfortunately, there was no box or manual with it.

msdos401-select-front msdos401-install-front

msdos401-install-rearThe two disks were labelled Select and Install.The disks were labelled with disk number 05806 for Install and 05807 for Select. It is copyright dated 1981-1988 which makes it at least a year older than I am.

That would make it a little bit of a challenge to get the data off.

There wasn’t much distinguishing on the underside except for a heat-pressed number into the disk jackets.

Even the media envelopes were not notable.

msdos401-envelope-front msdos401-envelope-rear


As usual, I got out my Kryoflux and Panasonic 5.25″ drive combination for the challenge. Increasing the sector retries to 150 was enough to get it read eventually but not without making lots of horrible squeaking and scraping noises. The magnetic material wouldn’t be around for much longer by the sounds of it.

dos4-d1 dos4-d2


I tried to boot the floppies on VMWare Workstation 8, only to find that it always complained that the CPU halted due to some illegal operation. Using VirtualBox was enough to boot from one of the floppies, but installing was not an option as the prompt asked to switch to the Select floppy, to which I did, but the system didn’t recognize. From the Kryoflux read-out, it’s not possible to verify the disk as not having being written over or possibly corrupted in the past – so maybe it’s not forensic quality.

Part of the reason may be because the disks have the notch cut out, enabling write on the diskettes. At least I could see the version string banner for the OS and interestingly, it does display the date and time correctly … maybe that has something to do with VirtualBox.



Maybe MS-DOS v4.01 is buggy, maybe the emulation is to fault – only when I try to run it from “period correct” hardware will I be sure. The Kryoflux results seem to imply the disk has additional data in the header and might have been rewritten on a consumer drive, so the archival quality of these disks are called into question. However, disks of this age are very fragile and efforts must be made to prioritize their recovery – so I got this one out of the way as early as I could.

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4 Responses to Tech Flashback: Microsoft MS-DOS Version 4.01

  1. sparcie says:

    Ah MS-DOS 4.01, that was the first OS I used as a kid back on the old 386sx! It seems you’re missing a disk or two, my set of disks has 6 disks. It came with the first version of the dosshell, and gwbasic, the language I first learned to program with. Fortunately I have proper disk images of my disks, although somehow a few had caught a boot virus called aircop that I’ve since removed. I could make a bootable hard disk image (if it works) for you to try out if you like.

    • lui_gough says:

      Thanks for the offer, but I think I’m perfectly content with MS-DOS 6.22 for now :). But that is one thing I should be careful of, the old boot sector viruses. Brings back memories … especially ones of “accidentally” leaving floppies of unknown trustworthiness in a computer and “accidentally” rebooting it. One day you might find the partition table gone, strange behaviour, random text “appearing”, etc.

      Also reminds me of the (almost entirely pointless) MSAV anti-virus from MS-DOS 6.22 that never seemed to find anything but (with the right options) liked to stash away a (or something like that) file in each folder with the file sums to look for alterations.

      – Gough

      • sparcie says:

        Yes 6.22 is much better, and there isn’t much to learn from 4.01. Even after having the bugs ironed out it was hard to make use of EMS or XMS memory. It was also missing some useful things like a mouse driver.

        Aircop is the only boot virus I ever saw in the wild fortunately, we never worked out where we got it from, probably a friend of my brothers with whom we occasionally traded disks. It is strange the DOS disks had it as they were copy protected (the notch had not been cut out and they were original disks). Perhaps the virus had worked out a way to circumvent the protection? Perhaps they got the virus at the factory or OEM, we basically never used those disks.

        I found an old version of the mcafee virus scanner on one of Dads old disks, and I have an old version of norton antivirus that should clean stuff up. I believe F-Prot or someone else has a free version of their DOS scanner you can use to check old disks.

  2. Interested_Blog_Visitor says:

    This article describes that MS-DOS 4.01 is working on MS Virtual PC 2007, even install is working, but you have to set some BIOS options first.

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