PolyMorphic Systems -  Floppy Disk Controller Board
This was the floppy disk controller board Polymorphic Systems used in their System 8813

This disk controller was one of several models built by PolyMorphic Systems. This, the earliest model, supported single-sided, single-density disks which stored 90K bytes per disk.  For comparison, the first IBM PCs used double-sided, double-density disks and stored 360K per disk.  The upper right connector went to a ribbon cable which connected to one, two or three Shugart SA-400 diskette drives.  This board was was used by some in the early Poly-88 board  system but it was really made for their 8810/8813 systems. The model 8813 had three floppy disk drives, the 8810 had only 1.  Later they had a double density version of the board.
  
Both the single and double density boards used 10 hard sectored disks. It seems that the double density board was also used for the 5.25 disk with a change in firmware (the board had its own Z80 processor). Polymorphic changed the capacitors in the PLL and the crystal frequency in the 8 inch controller to use it for 5.25 drives.

The System 88 manual gives a good description of the early state of the art for disk operating systems at the time as well as some general information about the board. I have not yet located a manual for the actual board itself.