I bought two install discs: Linux Mint 18.1 Cinnamon - Install/Live DVD (32-bit) and Ubuntu 16.10 Desktop - Install/Live DVD (32-bit). The Mint CD will mount on the hard drive of my iMac, but the Ubuntu won't.

The Mac refuses to read the Ubuntu disc, giving the message "the disk you inserted was not readable by this computer." But the Ubuntu disc will mount on a Dell laptop.

Any ideas?

CD or DVD ?!

Sorry, DVD.

CD or DVD it is formatted as a data disk. There are a couple of fairly obvious reasons why it cannot be read on your Mac...

• The disc uses a file format your Mac does not recognize or
• Due to variations in the dye used in the disc media and variations in the frequency and strength of the read laser in your drive, it cannot read the disc.

Since you have access to a PC that can read the disc, either could be solved by copying the disc contents to the PC then burning a new disc on a new blank using a file format you know the Mac can read preferably NTFS.

I guess it's the OS. I ordered another Ubuntu DVD, but it didn't mount either, though it did mount on the PC. Odd that Mint had no problem.