Just save the game normally. Don't put in a disk or anything.

The game will be saved to your mount point for the C: drive.  For example, If your mount point is `/Users/Foo/Documents/Zork/`, then the game will save to the `./save/` directory in the `./Zork/` folder.

When you want to resume playing, load up Zork then type `restore` at the prompt and press <kbd>Enter</kbd>.  It should point to your existing save file.  If not, type where your save is located, for example, `C:\Save\zork1.dat`, then press <kbd>enter</kbd>.