Altair Minidisk Support in the Altair Clone

Announcements about the Altair 8800 Clone including software and hardware updates.

Altair Minidisk Support in the Altair Clone

Postby AltairClone » July 30th, 2014, 10:55 pm

I have finished implementing support for the Altair Minidisk in the Altair Clone. The Minidisk is a 5-1/4 inch, hard sector floppy disk with a 70K capacity (versus 308K for the Altair 8 inch floppy). The Minidisk is also slower than the 8 inch floppy with a net maximum transfer rate of 10KB/s versus 24KB/s for the 8 inch floppy. To reduce media wear, the Minidisk shuts down the drive motor after about 6 seconds of drive inactivity. A one second delay is encountered whenever a drive must be started back up or the controller switches between two drives.

MITS provided both BASIC and Altair DOS for the Minidisk drive. Until very recently, copies of these disks were not readily available in the Altair community, but because of great work by M. Eberhard and S. Shepard, we now have a good collection of Minidisk images archived on the Yahoo Altair group website and on the support page of the website. Along with the standard MITS software, I have created CP/M 2.2 for the Minidisk drive as well.

In addition to the new Minidisk folder on the support page, I will soon post a firmware update for the Altair Clone that allows use of the Minidisk format. Emulation of the Minidisk in the Altair Clone is very accurate including the actual sector timing, head step timing, power on delay, shutdown timer, etc. The firmware update also includes some other important changes that will be detailed in another post on this forum.

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