The electronics are identical in the D9060 and the larger D9090 unit; the only difference is the size of the installed hard drive, with a jumper set to distinguish between 4 or 6 disk heads.

This DOS PCB is made up of several major electronic components: The main brain driving this controller is the AMD 'AM2910' (a 12-bit address sequencer) The SASI interface was invented by Shugart which would later become Seagate.

It appears the DOS was never fully completed by Commodore; this is indicated by the way two directories overlap for the one device and the number of blocks free is displayed as if only one hard drive is in use.

[2] Despite the small storage space (by current standards) of these legacy hard drives, formatting either can require a fair amount of patience from the user: These long delays can be attributed by the overall operation which consists of the low-level disk format by the SASI controller, followed by a six-pass test pattern write to the whole disk surface by the DOS before placing the initial filing system information.

But if you have scores or hundreds of files saved, then the user must wait some time until the entire directory listing has finished scrolling.

With minor changes to the CBM DOS ROM code, larger capacity hard disk drives could be swapped into the D9060/D9090 unit.

In the 1980s, an Arizona company named Copperstate Cash Register was selling upgraded units to the business and BBS operator community.

This has put pressure on the supply of these devices as nowadays they are wanted by both Commodore 64/128 users and also needed by people using the PET family of machines, that these drives were specifically designed for.