eBay
GMX-20 GIMIX Micro-20 68020/68881 Single Board Computer

The item up for auction is a working GMX Micro-20 68020 Single Board Computer
with SASI connected Xebec controller for the 200Meg harddrive and a 5.25" 720K
Floppy Drive .  This includes the original power supplies (separate 5vdc and 12vdc units)
and UNIFLEX operating system with assembler and Absoft Fortran 77 compiler.

This computer can be operated using the Windows XP hyperterminal  via serial port and
and the system can be structured in a multi-user mode with up to 4 terminals.  Screen
shots of  its startup are shown.

Documentation is thorough for the Debug, Uniflex System, Screen Editor and the hardware in
five (5) notebook volumes.  The Fortran 77 compiler is without documentation although the Absoft
Pro Fortran manual is available here.  Hardware circuit diagrams, timing and protocol is described
in detail with Motorola manuals for the 68020 processor and 68881 coprocessor .

While the original independent 5v and 12v power supplies are provided it can be powered
up using a 4 pin molex connector from a desktop computer  (normally harddrive power).

This is the 16MHz version of the board and the computer was assembled with all new components
except for the Xebec S1420 controller which was surplus from Xebec in Carson City.  This
controller supports the hard drive and daisy chained floppy drives. Another port allows an Atari
520ST computer to be the terminal (which earlier was my primary means of operating it).

The SASI (Shugart Associates Standard Interface) is a subset of the SCSI interface.  Most current
SCSI devices are compatible with SASI as added features of SCSI are seldom used.

This was assembled in 1986 with a million bytes of memory and was superior to most
mainframes of that time.  It has seen use for trajectory analysis, ionospheric modelling, GPS
reductions, radar vernier analysis and surveying closure verifications among other things and is in
working order.

A double density full height floppy is included as an added drive for greater interface flexibility
and it includes the necessary terminating resistors.

The cover was originally borrowed from a Heathkit Amp/Preamp but was reclaimed when that
unit was found to be a collectible.  Sales literature and original invoice are included.