Which model/product should I buy?

WD External Drives External Drives for Mac
2

Hello,

None of the new models officially support Mac OS 10.4, but you should be able to use them without any problems. 

These are some of the external drives, that officially support 10.4:

http://www.wdc.com/wdproducts/library/AAG/ENG/4178-705036.pdf

http://www.wdc.com/wdproducts/library/AAG/ENG/4178-705013.pdf

http://www.wdc.com/wdproducts/library/AAG/ENG/4178-705089.pdf

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