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PowerBook G4 1.5 12" has a Fujitsu MHT2080AH 75GB HD that is failing. Can an SSD HD be installed in the Powerbook? If so, what specs do I need to be aware of? Will a KingSpec T-60 SATA III 3.0 HD work? Does it need any kind of adapter? or spacer?

No. Your machine uses an Ultra ATA/100. Even trying to find a new one of these will be very difficult (I’ve looked and have not found one yet, only used.) update - here’s a new one: http://www.newegg.com/Product/Product.as… http://www.everymac.com/systems/apple/po…

Actually, if you are willing to build your own IDE drive you can do so as follows:

Buy an mSata of the size you need. mSata’s are miniature SSD Sata drives https://www.amazon.com/gp/product/B07GZF…

Buy and IDE to mSata converter in a case form https://www.amazon.com/gp/product/B01GRM...Put the two together and you have a SSD IDE driveFind instructions for installing an IDE in the 12” power book and away you go.