fluxengine/doc/disk-northstar.md

Disk: Northstar

Northstar Floppy disks use 10-sector hard sectored disks with either FM or MFM encoding. They may be single- or double-sided. Each of the 10 sectors contains 256 (FM) or 512 (MFM) bytes of data. The disk has 35 cylinders, with tracks 0- 34 on side 0, and tracks 35-69 on side 1. Tracks on side 1 are numbered "back- wards" in that track 35 corresponds to cylinder 34, side 1, and track 69 corresponds to cylinder 0, side 1.

The Northstar sector format does not include any head positioning information. As such, reads from Northstar floppies need to by synchronized with the index pulse, in order to properly identify the sector being read. This is handled automatically by FluxEngine.

Due to the nature of the track ordering on side 1, an .nsi image reader and writer are provided for double-sided disks. The .nsi image writer supports both single- and double-sided disks; however single-sided .nsi images are equivalent to .img images.

Reading disks

You must use a 48-TPI (40-track) 300RPM 5.25" floppy drive.

To read a double-sided North Star floppy, run:

fluxengine read northstar

To read a single-sided North Star floppy, run:

fluxengine read northstar -heads 0

You should end up with a northstar.nsi with a file size dependent on the floppy disk type:

Disk Type	File Size (bytes)
Single-Sided, Single-Density (SSSD)	89,600
Single-Sided, Double-Density (SSDD)	179,200
Double-Sided, Double-Density (DSDD)	358,400

Writing disks

You must use a 48-TPI (40-track) 300RPM 5.25" floppy drive and make sure that the drive's spindle speed is adjusted to exactly 300RPM.

To write a double-sided North Star floppy, run:

fluxengine write <format> -i image_to_write.nsi

...where <format> is northstar87, northstar175 or northstar350 depending on the format you want to write.

Useful references

• MICRO-DISK SYSTEM MDS-A-D DOUBLE DENSITY Manual. Page 33 documents sector format for single- and double-density.