I made a stupid profile just to answer your question, I like that my first apple forum response is to 'disneyland' so thanks disneyland for continuing to give us hope and answers to our live's questions... seagate is renowned for only working on windows. I see this questions constantly and never see a helpful answer so here it is... tell your friends. (answer includes: how to format normally, formatting advice, then how to format if your hd isn't showing up at all)
This goes for most external hd's used on mac, although its almost always the seagate hds that have an issue. When you buy a hd for your mac make sure you format it to the mac before putting information on it. heres how. 1. (command and space bar) 2. type in disk utility 3. click on the external hd, not your mac hd 4. click on erase, used to be called format on really old macs 5. click on format type "osx journaled" is fine, google the other options if you really want to know what they all do. 6. give it a new name and hit "erase" it is now formatted for macos
advice: if you use your device on multiple computers, format to mac first because it will still show on windows computers but msdos or other formats don't always show on macs. If you have a hd that has always been working on your mac then you did any software updates or you plugged it into a windows pc and now its not showing on your mac. you have to reformat it to the mac.
the answer everyones been waiting for... most mac users have a windows pc somewhere hidden in a closet or their parents still are using one and you just happen to be living in their basement with the computer in reach, you're in luck. Essentially you have to reformat the hd on a windows first then reformat it back to mac. Plug it into the windows, click around for 5 minutes reacquainting yourself with the nostalgia of how the heck did you ever use one of these, until you find the format button. After playing the old ms dos games still hidden on the pc like hero gold, lemmings, and minecraft format your hd. First format it back to default settings, clicking the quick reformat box makes it go faster and usually doesn't change the results. Even if the hd is brand new never used just out of the box and it isn't showing on mac, yes you still may need to get into the old cursed windows pc and format to default settings. Once you format to default plug it back into mac and erase/format to mac (see paragraph 2). If the hd still isn't showing on mac, go back to your windows, play some solitaire, and reformat the disk again. This time try not using the quick format, or try some of the other formats, they go quick. I just had to do this with a new 8tb seagate and made the mistake of not hitting the quick format, 30 minutes later I hit cancel and quick format. worked just fine.
*if you have important pictures of your ex data files on your hd that is now not showing up, make sure to save it elsewhere before erasing/formatting the hd. This will have to be done through the windows computer. yes it may corrupt your other hd in the process or download a virus or who knows, just try to minimize your windows exposure and finish the hd issues, unplug them, and make sure it all worked before spending the rest of the day week month playing your old roller coaster tycoon or sims obsession from childhood.
if none of this works, do what you used to do on windows, click around until something important-looking shows up, click around some more until it works. (how do you think I figured all this out in the first place)
