Virtual PC and Floppy Images

I use Virtual PC for Mac to run Windows 2000 on my Powerbook. I had some 3.5” floppy disk images from an MSDN disk that I wanted to use, but Virtual PC didn’t like them. I figured out why.

The floppy disks images need to be named with either .vfd or .dmg extensions. But, more importantly, they need to be the right size. They need to be exactly 1474560 bytes in size. The particular files I got off my MSDN CD-ROM were not exactly that size. Obviously whatever disk image creation software Microsoft used didn’t bother to store a whole lot of zeros at the end of the floppy disk image. It only stored the data.

Using a command prompt, here’s how I created the proper size floppy disk image. I’m just concatenating a bunch of zeroes on the end of the existing image.

  1. Find out how many zeros you need. Subtract the size of the disk image from 1474560. I did that this way:

    echo ‘1474560 - 1424460’ | bc
    The answer is printed out (50100 in this case).

  2. Create a file with that many zeroes in it. I did it this way:

    dd if=/dev/zero of=padding bs=50100 count=1
    That creates a file named padding that is exactly 50100 bytes of zeroes.

  3. Concatenate them. thus:

    cat originalImageFile padding > diskImage.dmg
    Now I put that file in my Virtual PC folder. (~/Documents/Virtual PC Lists for me). I can capture them and use them now.