I have several hard drives from a few years ago, some that I have never used and some that I have, and when I plug some of them into my Mac, I receive a message that it is unable to initialize the drive and they do not show up in the computer. I'm afraid of formatting the drives in case these drives might have some data on them.
Does this message mean that the drives have never been used? They were all purchased at the same time, and I do not remember having to format any of them in order for them to show up on the computer.
No, that just means the format of your hard drive is not recognized by MAC, maybe you used it in Windows OS, therefore it ask you to initialize hard disk, if possible you could try to connect to Windows OS to test it could be recognize or not.
There are at least two possibilities. One is as quesionboy said - the drives have been Partitioned and Formatted and contain data, but not in a system that your Mac can recognize. You would need to try them in other computers using other OS's (Windows, Linux) to determine whether that is the case.
The other possibility is that these are actually completely empty brand new HDD's that nobody ever has used. ALL new HDD's MUST be Partitioned and Formatted (sometimes called Initialized for both steps) under the OS where they are to be installed and used. Until that is done, the drive is completely useless, and it won't show up in your computer's OS in any way (except in utilities for the Initialization process). You say, however, that the message you get is not that the drive(s) can't be used, but rather that the drive(s) cannot be Initialized. I do not work with Macs so I'm not sure whether that term means the same as in the Windows world - Initialize usually means establish Partition(s) and Format it (them) - or whether it means just that the system cannot understand the data already on the drive and start to use it (similar to some Linux messages). Hopefully there are some Mac gurus around that can help straighten this out.