cctech Digest, Vol 44, Issue 47

The only Heath disk operating system offered by Heath for the H-11 was HT-11, which was a very slightly modified (dumbed down) version of DEC's RT-11. The only disk system offered by Heath was the H-27, dual 8" [Memorex SSSD] drives. Many customers wanted to buy genuine DEC RT-11, which would run on the H-11/H-27, but it was about $2,500 (and the differences from HT-11 to RT-11 were very, very few). HT-11 was "cheap", but it would only run on the H-27, it would not work on a non-Heathkit DEC floppy disk system. The H-27 had two modes, "Heath" and "DEC", to prevent HT-11 from being used on non-Heath H-11's. I don't recall if there was paper tape software for the H-11 or not (I think that there was), but even if there was, no one used it very much. The Heath paper tape reader, the H-10, was a mechanically unreliable nightmare (mostly the punch, the reader worked ok), but they are worth a lot of money today, I've seen them go on E-Bay for over $600. HT-11/RT-11 was no prize; it was a low level contiguous file operating system, less sophisticated even than CP/M, although it may have had some better utilities (and, for those to whom it mattered, it was of course "more DEC-like"). The H-27 was just two standard 8" drives in a case with a Z-80 based intelligent controller (WD1771 disk controller chip) that talked to the H-11 using what we would now call a "host adapter" over a proprietary bi-directional parallel port. The interface and command set wasn't any of the standards for this type of configuration (e.g. it wasn't SASI or SCSI), but it used that type of architecture. For a number of years I used an H-27 on an S-100 system with a Tarbell controller by simply disconnecting the internal intelligent controller and running a 50-pin cable direct to the two Memorex drives. They were Shugart SA-801 compatible, so it was an easy configuration to use, the H-27 then being just two drives, a power supply and a cabinet.