The earlier discussion:
https://discussions.apple.com/thread/5060417 .
See the information starting on page 54 in the referenced PowerBook 190 manual (http://manuals.info.apple.com/en_US/0306899APWRBK190UG.pdf), and especially the parts about how to use the PowerBook as a hard disk (SCSI disk mode).
The cable of primary interest in this case would be the Apple HDI-30 SCSI Disk Adapter Cable. This is a cable with an HDI-30 plug (with 30 pins) one end and a CEN-50 connector the other end. The HDI-30 plug is connected to the HDI-30 SCSI port of the PowerBook 190 (the computer will use SCSI disk mode when it detects the 30th pin). There are other variants, including solutions with a separate switchable adapter HDI-30 to DB-25.
In order to link the two computers together, various cable combinations are possible (CEN-50 or DB-25 connectors, as needed), partly depending on whether other SCSI devices are involved or not. The SCSI port of the desktop computer is DB-25. Also, please note the terminator requirements (the terminator could, for example, be a CEN-50 pass-through model).
See also http://support.apple.com/kb/TA21592 .
Jan