Creating an MS-DOS floppy image from a directory in Unix

For a long time I have needed a way to transfer data into my DOS virtual machines. I came somewhat close to a solution by using Keka to archive directories as ISO files, but I was unable to create what I truly needed – a floppy disk image containing the archived contents of a directory. Well, now I’ve found a way to do just that, partly by doing some research on Google and partly by just figuring stuff out on my own.

The first thing you need to do is create a 1.44 MB empty file with an extension of .ima, .img, or some other raw floppy image extension. This can be done using dd, with the following command:


dd if=/dev/zero of=floppy.img bs=1024 count=1440

I took a screenshot of the output of dd for a visual:

dd

The next step is to format the file with an MS-DOS FAT filesystem.  The easiest way to do this is in DOS.  So insert the blank disk image in the VM and type format a:

format

Now you have a blank floppy image and are ready to add files to it.  To verify that the floppy had been formatted, I ran a hexdump in the Unix terminal.

hexdump

Next you need to mount the floppy image.  The easiest way to do this is to just double click on its icon in the GUI, then copy and paste the files from the source directory or directories to the directory that the image is mounted on.  I tested this first with a couple of simple standalone programs – Visicalc and DOS Cal:

adrive

Now I have installed two programs: CAL.EXE and VC.COM. Indeed, when I go to the C: drive and type cal, the program starts.

cal

Just a side note here: the default path in MS-DOS is set to C:\DOS, so if you want to run programs from a different directory you need to edit the search path in the AUTOEXEC.BAT file:

edit-path

For some reason, my DOS VM would only read the first floppy image that I created. Creating further floppy images using the same technique resulted in an Abort-Retry-Fail error message. To work around this, I have written a C program that automates the process of creating and formatting the floppy image, using the hexdump of the original image. That way I know the file will be exactly the same and I’ll be able to create multiple floppy images for software that requires a multi-disk installation. I will talk about this program, as well as MS-DOS 6.22, MS-DOS disk labels, and some additional software that I’ve installed in the next few blog entries. For now, farewell.

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A Tale of Three DOS’s

This is a story of how I got into DOS. The story begins back in Summer 2009 when I first started playing with the DOS prompt in Windows. I actually preferred the Unix CLI because it was more rich in features, but the DOS prompt had its own charm to it. The font was aesthetically pleasing, and the format of the commands had a certain novelty to it (and I’m a sucker for novelty). I actually started playing with the DOS prompt in my Java class. It wasn’t my first experience with it, as we had written programs that ran in DOS in my C++ class the previous Fall. But it was my first time experimenting with the commands.

I was greatly intrigued by the DOS command line and wanted to learn more, and in early 2010 I started looking for a DOS emulator that I could run on my Mac. I found Boxer and then DOSBox, and soon I started playing a slew of MS-DOS games – Duke Nukem 3D, Kingdom of Kroz, Nethack, and Stargoose to name a few.

Eventually I wanted to try the real MS-DOS. I downloaded an archive for the MS-DOS 5.0 installers from vetusware.com, and also downloaded VirtualBox so I could run the DOS. I had to get help from the VirtualBox forums as to how to use the floppy disk images that came in the archive; they were in the .IMA format, which I was completely unfamiliar with. I thought I needed an ISO file, but it turned out I didn’t. I just inserted the floppy images into the virtual machine’s floppy drive.

Here ‘s a slideshow of the installation process for MS-DOS 5.0:

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Of all the operating systems I’ve installed, I would say MS-DOS was probably the easiest.  It required very little configuration and I didn’t have to partition the drive beforehand.

In later versions of MS-DOS (including 5.0), the default configuration is for DOS to boot into a semi-graphical shell called DOS Shell, which can be activated manually with the dosshell command.

MS-DOS-Shell

The weird thing is, I had had a dream a few months earlier of using MS-DOS with a graphical interface.  This was exciting, because it was like my dream had become a reality.  Only in the dream, the DOS shell was all greyscale, so I set DOS Shell to black and white, 4-color to make it more like my dream.

I have a lot of dreams about old computers and old operating systems, and one of the recurring themes in my dreams is DOS.

If you’ve ever used both the DOS prompt and the real MS-DOS, you will know that MS-DOS is nothing like the DOS prompt in modern Windows.  It’s a whole lot more.  A list of some of the commands in MS-DOS:

backup and restore MS-DOS’s equivalent of the Backup and Restore Center
doskey A useful utility for things like command history, macros, etc.
qbasic A BASIC interpreter for MS-DOS
undelete Instant data recovery; undeletes a file that has been deleted

There are also some nifty programs and games written with QBASIC. Since they’re not in binary form, you can modify them yourself with the QBASIC editor. One that I started using was Microsoft Money Manager.

Money1

Money2

Money3

At this point I wanted to explore some of the other DOS’s out there.  I was very interested in DR-DOS and PC-DOS.  I had downloaded and used the default text editor for PC-DOS and found it to be a lot more full-featured than MS-DOS Editor.

The next DOS that I downloaded was DR-DOS.  Again, I downloaded it from Vetusware.  The installer came in the form of five floppy images with the extension .144, a rather obscure format and one that VirtualBox doesn’t recognize.  I was faced with the challenge of converting these images to a format recognized by VirtualBox.  To achieve that end, I wrote this shell script (thanks to the people in the VirtualBox community for supplying the dd command):


#!/bin/bash
# One-time script converts .144 floppy images
# to .IMA floppy images.

for (( i=1;i<=5;i++ ))
do
        touch disk0${i}.ima;
        dd if=disk0${i}.144 of=disk0${i}.ima bs=512 count=2880;
done

DR-DOS is somewhat harder to install than MS-DOS. It makes you partition the hard drive and select a partition before installing the OS, though much of this process is automated.

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It took a couple of tries, but I eventually got it installed.  I found the OS to be rather delightful.  It has a few additional commands that MS-DOS 5.0 doesn’t have (I don’t know about 6.22).  For example, there is the stacker command, which activates the stacker driver, a disk compression utility.  I plan to explore this at a later date.  Also, the help is a lot more comprehensive, featuring not just a list of commands, but an entire book on DR-DOS and its features.  There’s networking with Personal Netware, which I’m not sure I’d be able to do in VirtualBox, but it’s worth exploring.

DR-DOS 1

DR-DOS 2

DR-DOS 3

The other DOS I tried was FreeDOS.  This is a fully modern open-source clone of MS-DOS that combines features of DOS with some Linux-like features.

This is the FreeDOS startup screen.  From here you can either install FreeDOS from an install disk, boot from a live version, or boot from the hard drive.

VirtualBox_FreeDOS 1

Here’s a brief slideshow of the FreeDOS installation process:

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One of the things I really like about the FreeDOS installation is that it comes with 4DOS preinstalled, and it gives you the option of booting into either 4DOS or the default FreeDOS shell.  4DOS is a shell for FreeDOS that emulates some Unix-like features, as well as giving you some options that are pretty much unique to 4DOS.  One of these is the ability to add descriptions to your files, with the describe command, so that when you type dir, you get something like this:

4DOS

I just thought this was so cool, because no other shell lets you do this; no other shell that I know of anyway.

Well, that’s about all I have to talk about for now.  This entry has dragged on long enough, and I think I will say goodbye now.  Goodbye now.