378Kb disk hack for Fractint 15.1

I first heard of Fractint soon after I got interested in Fractals. I knew it was very fast and had lots of fractal types and features and I wanted to run it on the PC1512 (the only PC I had regular access to at the time). I bought a "Computer shopper" magazine which had a copy of Fractint 15.1 on the cover disk. Only the 3.5" disk was available, so I had to get a friend who had both drives to copy it onto 5.25" disks for me. The disk contained a 323Kb self-extracting ZIP file which, when ran, produced (amongst other files) FRACTINT.EXE which was a 384Kb file. This would not have been a problem except that the machine only had 360Kb disks - FRACTINT.EXE wouldn't fit!

Somewhere (probably on another magazine disk) I found a program that was able to format disks to non-standard formats by calling BIOS functions (or possibly by programming the drive controller directly, I don't remember). It turns out that the drives in the PC1512 were actually able to format 42 tracks before the head bumped into the stop, not just the standard 40. This gave me a 378Kb disk, still not quite enough. I discovered that if I requested the program to format a 44-track disk, it would fail but record in the boot sector that the disk was 396Kb. With this format, I was able to persuade the ZIP program to try extracting FRACTINT.EXE. Of course, it failed to write the last few Kb but it turned out that because Fractint used overlays, it still worked - only one or two of the overlays were inaccessible (I think printing and shelling to DOS were broken, and I didn't miss them).

I made a Mandelbrot zoom video with this setup. It was on the point +i (zooming into a more detailed area would have taken too much time and disk space). I played the video back by converting the images to PCX files (which are much quicker to decode than GIFs) copying them to a ramdrive and then using PICEM to play them back at about 5fps.

One Response to “378Kb disk hack for Fractint 15.1”

  1. Scali says:

    Ah yes, I remember that program!
    Or at least, I used one of those, not sure if there were others.
    It was called FDFORMAT. You could tweak tracks and sector counts and such.
    Another very nice feature was its custom bootsector: it would automatically boot the HDD for you.
    Back in those days it was a very valuable feature, since you could not disable floppy boot in most BIOSes. So if you accidentally left your floppy in the drive when you booted up, it would try to boot from the floppy. You'd have to remove it and press a key to boot from HDD. With an FDFORMAT-formatted floppy, it would just boot the HDD immediately, so you could leave your floppies in the drive without worrying.

    I was intrigued by this, so I disassembled the bootsector myself to see what it did. Turned out it was really simple: it would just use some BIOS routines to load the first sector of the HDD to the right segment and jump to it.
    I later used this trick to make my own custom bootsectors, which would show a message or even some simple graphics, and booted from HDD when you pressed a key.

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