HDD size limitation on Mac?

I was wondering the same thing. The Operating System portion of the answer depends on what version of OS you are using, and what filesystem is in use on your drive.

Unfortunately, the link above describes System 7, which was first introduced in 1998, and is hardly used today (except where upgrading old machines). Development on Mac OS 9 (2 major versions since 7) stopped in 2002.

If you are putting in a new drive, upto and including OS X 10.5, you could use HFS a.k.a. "MAC OS Standard", which was limited to 2TB Volume Size and 2GB file size. Snow Leopard (10.6), Lion (10.7) and later users can no longer write to or partition a new drive as HFS; it has been replaced by HFS+ / HFS "Plus" / MAC OS Extended.

For HFS+, check the Apple Support knowledgebase for exact file and (disk) volume size supported at each version of MAC OS X. You'll have to translate the name (e.g. Tiger) to a version number (e.g. 10.4). Search for "HT2422 - Support - Apple" (Forum restrictions prevent me from posting link.)