Classic capability by machine age

This is a mirror of the original tip that was found on Apple's website.  The tip is now maintained on the mirror by
Macs of different ages have different capabilities when it comes to Classic. The dates below are when specific models were released as new Macs according to the spec pages:

11/1997-7/2002 The G3 and G4 Macs released during this period (except the original G3/250 Powerbook) can use the 9.2.1 retail installer disc to install Mac OS 9. If they shipped with a version of 9, they can only use a newer retail version of 9 to install 9 for use with the Classic environment. A minimum of 9.1 needs to be installed to use Classic. The article below lists which versions of 9 each Mac shipped with:

Mac OS: Versions, builds included with PowerPC Macs (since 1998) - Apple Support

If you need to upgrade to 9.1 or higher, follow the directions in these articles:

Mac OS 9: Available Updates - Apple Support

How to find Mac OS 9 downloads?

Also check if the firmware needs to be updated before installing 10.2 or later:

Mac OS X: Available firmware updates - Apple Support

8/2002-12/2002 The Macs which shipped new during this period shipped with a restore 9 installer disc and could not use the retail installer disc for Mac OS 9. Call AppleCare if you are missing those discs:

To install Classic from the restore discs, follow the directions in this article:

867 Mhz Macs and faster Macs that shipped during this period 11/1997-12/2002 can also boot into 9 when Leopard (10.5) is installed, but can't use Classic unless Tiger (10.4) or earlier is installed on a separate bootable hard disc, or partition of the boot hard drive. Pre-Firewire 800 Powermac G4s which shipped during the next time period also have this ability if they were 867 Mhz or faster.

1/2003-12/2005 The machines which shipped new during this period (except the PowerMac G4 pre-Firewire 800 which could boot into 9) could only use Classic, and thus once upgraded to Leopard can't use Classic anymore. If you kept a separate partition or booted off an external hard drive that had Tiger they could continue to use Classic. Article still applies for restoring Classic to Tiger and older operating systems on these Macs.

1/2006 - present Intel Macs which shipped during this time period can't use Classic at all.