100tpi MetaFloppy disks

Micropolis MetaFloppy disks use MFM and hard sectors. Mod I was 48 TPI and stored 143k per side. Mod II was 100 TPI and stored 315k per side. Each of the 16 sectors contains 266 bytes of “user data,” allowing 10 bytes of metadata for use by the operating system. Micropolis DOS (MDOS) used the metadata bytes, but CP/M did not.

Some later systems were Micropolis-compatible and so were also 100 TPI, like the Vector Graphic Dual-Mode Disk Controller which was paired with a Tandon drive.

Important note: You cannot read these disks with a normal PC drive, as these drives are 96tpi. The track spacing is determined by the physical geometry of the drive and can’t be changed in software. You’ll need to get hold of a 100tpi Micropolis drive. Luckily these seem to use the same connector and pinout as a 96tpi PC 5.25” drive. In use they should be identical.

While most operating systems use the standard Micropolis checksum, Vector Graphic MZOS uses a unique checksum. The decoder will automatically detect the checksum type in use; however, a specific checksum type may be forced using the --decoder.micropolis.checksum_type=TYPE where TYPE is one of:

Checksum Description
AUTO Automatically detect
MICROPOLIS Standard Micropolis (MDOS, CP/M, OASIS)
MZOS Vector Graphic MZOS

Later versions of the Micropolis format supported ECC, especially in controllers with HDD support. The ECC can detect and correct errors. However, it is unclear what ECC algorithm was used by each vendor. ECC is disabled by default, but available for checking and correcting using --decoder.micropolis.ecc_type=TYPE and for writing from IMG files using --encoder.micropolis.ecc_type=TYPE, where TYPE is one of:

ECC Description
NONE No ECC processing enabled
VECTOR Vector Graphic Dual-Mode Disk Controller

The CP/M BIOS defined SELDSK, SETTRK, and SETSEC, but no function to select the head/side. Double-sided floppies could be represented as having either twice the number of sectors, for CHS, or twice the number of tracks, HCS; the second side’s tracks in opposite order logically followed the first side (e.g., tracks 77-153). Micropolis disks tended to be the latter. FluxEngine always emits CHS format disks, so you may need to apply extra options to change the format if desired.

Options

  • :
    • 143: 143kB 5.25” SSDD hard-sectored; Micropolis MetaFloppy Mod I
    • 287: 287kB 5.25” DSDD hard-sectored; Micropolis MetaFloppy Mod I
    • 315: 315kB 5.25” SSDD hard-sectored; Micropolis MetaFloppy Mod II
    • 630: 630kB 5.25” DSDD hard-sectored; Micropolis MetaFloppy Mod II
  • vgi: Read/write VGI format images with 275 bytes per sector

Examples

To read:

  • fluxengine read micropolis -s drive:0 -o micropolis.img

To write:

  • fluxengine write micropolis -d drive:0 -i micropolis.img

References

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