This is an old revision of the document!
According to this website and also my own experience with disassembling and documenting these computers. The very easy way to tell the difference between the 4 types of tower models is to specifically look near the power button area on the front and the LED/buttons in the front. Pay attention to it carefully.
Generation 1
MODEL 1, MODEL 2, S1, S1
Parts are not as interchangeable. Requires a SCSI card in order to use hard drives which are external only. Power Supply card different than other 3 generation tower models.
https://img.aucfree.com/x698958405.1.jpg
Generation 2
“F” Family of parts
https://auctions.afimg.jp/m194866847/ya/image/m194866847.1.jpg
Generation 3
“0F” Family of Parts
Generation 4
CX Family of parts
