What version of macOS is pre-installed on the "Tapered Edge" Aluminum iMac models?

The "Tapered Edge" Aluminum iMac models originally shipped with a version of OS X Mountain Lion (10.8). Subsequent models initially shipped with Mavericks (10.9), Yosemite (10.10), El Capitan (10.11), Sierra (10.12), Mojave (10.14), or Catalina (10.15).

Specifically, these systems first shipped with these operating system versions:

The "Late 2012", "Early 2013" and "Late 2013" iMac models cannot run versions of the macOS past Catalina (10.15), and the "Mid-2014", "Late 2014" and "Mid-2015" iMac models cannot run versions of the the macOS past macOS Big Sur (macOS 11). Subsequent models are capable of running later versions of the macOS.

Can the "Tapered Edge" Aluminum iMac run Mac OS X software written for the PowerPC processor?

No. No "Tapered Edge" Aluminum iMac models run versions of OS X prior to OS X 10.8 "Mountain Lion." Mac OS X 10.6 "Snow Leopard" is the last version of Mac OS X that supports Mac OS X software written for the PowerPC processor via the "Rosetta Universal Binary Translator."

If support for older software is important to you, you likely would be better off purchasing a used Mac capable of running Mac OS X 10.6 "Snow Leopard." This version of the operating system is capable of running a great deal of Mac software written for Intel-based Macs as well as the majority of Mac OS X applications written for PowerPC-based systems, too.

In addition, versions of the operating system earlier than the one that shipped with a particular Mac typically are not compatible. Mac OS 9 applications are not supported by operating system versions compatible with the "Tapered Edge" Aluminum iMac line, either.

Also see:

• Which Macs can run Snow Leopard (10.6), Lion (10.7) and Mountain Lion (10.8), all three?
• What is Rosetta? What does it support?
• Are there any third-party programs to run Mac OS 9/Classic applications on Intel Macs?

How do you install software on the "Tapered Edge" Aluminum iMac without an optical drive?

Of course, you always can install software downloaded directly from the Internet.

To install software still compatible with recent versions of the macOS, or transfer files, from an increasingly vintage CD or DVD to a "Tapered Edge" Aluminum iMac (model numbers A1418, A1419, A2115, and A2116), you have to either use the "Remote Disk" function or purchase an external optical drive.

To use the "Remote Disk" functionality, you just install the software on a nearby Mac or Windows machine with an optical drive and "borrow" its optical drive to install software or transfer files via CD or DVD.

Additional information regarding "Remote Disk" is available via the Apple Support Site. It also is worth noting that "Remote Disk" cannot be used to re-install the operating system and some copy-protected CDs, DVDs, and games cannot be installed using this method, either.

Photo Credit: Apple, Inc. (SuperDrive - Left), OWC (Blu-ray Options - Right)

If you prefer to just purchase an optical drive -- which can be quite useful for inexpensive backups as well as occasional software installation -- site sponsor Adorama has the official aluminum Apple SuperDrive for US$79 and Other World Computing has a variety of third-party external optical drive options, too.

How do you restore the operating system on the "Tapered Edge" Aluminum iMac models?

Apple does not include a physical restoration method for the "Tapered Edge" Aluminum iMac line. Instead, the operating system has a hidden "restore" partition containing an "OS X Utilities" application that is only accessible upon startup by holding down Command-R.

Additional details about "OS X Recovery" for these models is available on the Apple Support Site.

Can the "Tapered Edge" Aluminum iMac run Windows or Linux?

Like every other Intel-powered Mac, the "Tapered Edge" Aluminum iMac line is capable of running Windows and a number of distributions of Linux via Apple Boot Camp or by using "virtualization" software.

For more information regarding Windows on the Mac, please refer to EveryMac.com's extensive Windows on Mac Q&A.