1) External drive must supply termination power (the power supply in the Plus is too feeble to do the job, so the design team decided that the external box should supply term power).

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Is that necessarily so? The floppy port on a Plus has the power to drive an external disk. so why can't the psu provide exterminal termination power. I took my figures from this site: http://www.scsita.org/aboutscsi/SCSI_Termination_Tutorial.html

Effective termination resistance = 132 ohms

Nominal voltage = 5 volts

Nominal term power = 0.19 watts

That sounds pretty reasonable to me. Termination power is also going to be fairly steady, whereas floppy drive power consumption is erratic.

Eliminating that 0.19W made sense for PowerBooks (everyone else who put SCSI in early portables made the same choice), but the Plus didn't need that problem.