Figured I should hit the Sega TeraDrive up with some diagnostics and found out some things I didn’t know.

1. The embedded SEGA startup environment appears to be based on PC DOS 3.x, and the version running here reports PC DOS 3.30. This is separate from the IBM DOS J4.0/V software Sega supplied with the TeraDrive.

PC DOS 3.30 was released on 2 April 1987 and added support for 1.44 MB 3.5-inch floppy disks. My TeraDrive Model 2 is equipped with two of those drives.

2. My TeraDrive documentation has a date of May 1991 inside the cover of both books. The chips inside the TeraDrive are timestamped week 09 1991, week 48 1990, week 06 1991 and week 08 1991. The IBM-branded BIOS is dated 22 March 1991. These component date codes place the machine firmly in the TeraDrive’s launch period, but they cannot establish its exact final assembly date.

3. The SEGA startup environment exposes a small RAM disk or virtual drive that is 242,176 bytes large. There is even 87,552 bytes free on this drive. The label is LOADER 1.0. It reports 1 head, 16 sectors and 130 cylinders. Pretty neat. Read speed seems to be around 1300 KB to 1400 KB/sec.

4. The diagnostic reference I was using associated one beep with a DRAM refresh failure and nine beeps with a ROM BIOS checksum failure. Those mappings are standard AMI BIOS codes, however, and I have not found model-specific documentation confirming that the TeraDrive’s IBM-branded BIOS uses the same POST beep scheme.

5. The diagnostic software identified the VGA controller as a Paradise/Western Digital WD90C22. Later hardware documentation identifies the actual chip fitted to the TeraDrive as a Western Digital WD90C10-LR, so the diagnostic appears to have identified a compatible controller family rather than the exact device.

Sega officially specifies 256 KB of VGA VRAM. The actual WD90C10 hardware is therefore more useful evidence than the software identification string.

The full set of Sega TeraDrive Model 2 and Model 3 photos can be found in the photo gallery.

Sources