I have two Seagate Barracuda 500GB internal SATA driver. Until recently, both were working well. When one stopped working, I found thhat neither compuer would recognize it (Kubuntu 12.10 and 13.04 alpha). My Seatools disc won't test either of them. Is there a different Seatools for SATA? I couldn't find that info on their website. I did find the apparently defective disc is still under werranty, but the pive non-working PATAs are not--no surprise as they are several years old. The surprise is the the remaining working PATA is the smallers of the lot, 80GB. I am concerned that Seagate mentions Windows and Mac OS, but doesn't mention Linux. Should I look for another mfr. next time? If so, which one?

I'd be more inclined to believe the sata controller or some bios setting is to blame.

Hard drives are dumb devices for the most part. The OS has little interaction with it as a brand name.

Seagate is as good as any other manufacturer of harddisks when it comes to Linux support.
Many harddisk test programs that are based on DOS have problems recognizing the harddisks if the controller is set to AHCI or RAID mode in the BIOS, I would check that first.

It would be hard to believe that a HD manufacturer would decline the big Linux server market!
I would expect a hardware problem.

Every time I had problems with hard drives, it was for every operating system, usually due to some hardware problem. Please, check the BIOS settings as well as the connection cables.
You could connect one drive only on the computer to check it.
I recently had both (IDE) hard drives on a Pentium4 tower not recognised at all. I found that one of them (secondary on the ribbon cable) was dead (12 year old 20GB drive! ) and prevented the master (40GB same age seagate) to be detected by the BIOs. After disconnecting the dead drive, everything else did work as expected.