Its to plug in an external floppy drive such as the 4869. I found the cable
for it on ebay. The P75 looks the same, but a bit thicker and has SCSI. I
have both models.
What OS are you running on each of them? I'm thinking that
this could make an interesting portable LINUX workstation and it
would appear that most of the MCA hardware such as SCSI and NIC cards
are supported under it.
Jeff
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Power Computing PowerCurve, 400mhz G3, Mac OS 9.0.4
Collector of Classic Microcomputers and Video Game Systems:
http://www.geocities.com/siliconvalley/lakes/6757