This page discusses the disk included with the Zip drive. I assume Jazz drives are similar but I have not used one myself. The following does not apply to any disks purchased separately.
The disk that comes with the Zip drive has two partitions and is write protected. It includes both an Apple filesystem and an MSDOS (FAT) filesystem. Each filesystem includes a copy of the Iomega tools for that platform. When you do a standard install the installation program on the included floppy copies off the tools for your platform and deletes the filesystem for the other platform. This then leaves the disk unwrite protected and free to be used with Irix .
However, since the write protection is done by the drive hardware, if you try to use this first disk on an SGI (or any other system) before you have done a Windows/Dos or Macintosh installation, you will find the disk write protected. There are two ways around this:
The following is thanks to William R. Bishop (firstname.lastname@example.org)
I am surprised this did not come up before, but I guess most of us played with that first disk immediately, doing the equivilent of (2) above, before using my format_zip program, which will fail on a write protected disk.
As a side note: If you also want to use the Iomega tools on both PC and Mac platforms, you can get both sets of tools off that original disk, just do a manual install of the guest program on each platform, and copy the tools off the disk. You can then either reformat the disk or do a standard install to get the disk unwrite protected.