The Hard Disk 20 Startup disk is the boot disk that is required for using the Apple Hard Disk 20 (HD20), the Apple hard disk that connects via floppy port, with a Macintosh 512k. The .sit archive on this page contains 4 files: .dart, .img, and .image files of the floppy, as well a a folder containing the data checksum for the DiskCopy 4.2 and DART 1.5.3 images.
To use, start up your Macintosh. When you see the floppy disk icon, insert the disk. After a moment, the disk will be ejected, and your Macintosh will begin booting from the HD20.
The Startup disk is only required when using an HD20 with a stock Macintosh 512k with a 64k ROM. If using a Macintosh 512ke (or a 512k that has had its ROM upgraded to the 128k version) then it is no longer required, as the data needed in order to use the Hierarchical File System ("HFS"; as required by the HD20) is now built into ROM.
Macs with a floppy port, that were released after the 512k (such as the Plus or SE), also do not require the Hard Disk 20 Startup disk, and should boot directly from the HD20 (with a properly blessed System Folder) without intervention.
Minimum system requirements
System 2.1 / Finder 5.0 (System 3.0 / Finder 5.1 highly recommended)
