Time Machine Hard Drive question

I am about to set up Time Machine ("TM"). As I understand it, I need separate external hard drive to do this, or at least this is preferred.

I currently have an external hard drive which my iMac does not recognize for use with TM. So my question is: what kind, make, etc., external hard drive do I get so that TM will recognize it?

Did you format the hard drive? TM can only use hard drives that are formated to Mac's format. Most hard drives are not pre-formated for Mac usage. You can basically use any hard drive with Macs.

The external hard drive mentioned in my first post was used on my pc. Am I to assume that any new external hard drive I buy can be used with Time Machine on my iMac?

Pretty much. The drive will most likely need to be reformatted since most are not pre-formatted for Mac. That's a simple process that can easily be done with Disk Utility. Here are a few other tips that might help you getting started with Time Machine ATPM 15.03 - How To: Time Travel: Introduction to Time Machine

tadd5181 said:

The external hard drive mentioned in my first post was used on my pc.

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That is the cause of your problem. If you no longer want to use it for your Windows machine then reformat the drive to Mac's Extended Journaled using Disk Utility.

Windows and Macs use the same hard drives. The only difference is that you have to format the drive for use in whichever OS you intend to use it with.

I want to continue to use the PC external hard drive as I am using or about to use Windows 7 on the iMac. So, I guess I will get a 2d external hard drive in order to use Time Machine.

Yes a second external is the way to go.

It is possible to format a drive so that it handles both HFS+ and NTFS file systems on the same drive though you have to partition the drive. I tried this procedure briefly but have never tried it for use with Time Machine. The procedure can be found here Create an HFS+/NTFS/FAT32 external drive - Mac OS X Hints

This tip describes the addition of a FAT32 partition but i think that is optional. If you decide to try this I suggest reading all of the comments - some of them describe improvements/shortcuts to the procedure as well as its limitations.

It is possible to have both but I personally don't like doing so which is why I didn't mention it. This does not mean that a person can't do so if that's what they want.

Putting all your backups on one drive is convenient but that does mean that if your drive fails then you lose everything. Also depending on how often a person adds and deletes files, Time Machine can use up hard drive space pretty quickly so the partition has to be big enough for TM to use now and in the future. If it fills up too quickly then he won't get the benefit of longer time line backups.

But Slydude you are right it is possible and everyone needs to decide for themselves if it is worthwhile for them to do so.

That's why I suggested reading all of the posts in the thread. I haven't run a drive like this in quite a while and then only ran it for a short time. Just wanted to make sure all the options were out there.