Upgrade Paths for Macs running Intel CPUs

This is a mirror of the tip on https://discussions.apple.com/docs/DOC-13695 stored to retain the original formatting after the communities formatting change of 2018.
It is maintained on my website, which may get compensation for me.

The table below includes the Machine ID/Model Identifier, that comes from the System Profiler, found under Apple menu -> About This Mac -> System Report -> Hardware.

This shows the upgrade paths up to Catalina for all Intel Macs, and their Model Identifiers.    

Each row in the table indicates the earliest Apple supported Mac by each starting OS and end OS configuration.

Note the horizontal scrollbar on the bottom of this tip to show the Mac Pro compatibility is beyond the width of this tip's layout.  

Every Mac released on or after an operating system release can't run an older version of Mac OS.  The one exception is Mac OS X 10.6 Server which can run on Parallels on newer Macs.  For more on release dates, see the identifying articles are found on this tip:

How to find your Mac's model and age?

10.6 compatible - 10.6.8 MacBook 1,1 iMac 4,x MacBook Pro 1,x Mac Mini 1,x
10.6.3 to 10.7.5 compatible MacBook with removable battery iMac 5,x; 6,x (Late 2006) MacBook Pro 2,x

Mac Mini 2,x
late 2007

MacBook Air 1,x
early 2008

Mac Pro 1,x-2,x
2006 through early 2007

10.8  - 10.11 preloaded with 10.4 Late 2008 MacBook Aluminum 5,1 iMac Mid 2007 7,1 mid 2007 MacBook Pro 3,1 - 4,2
10.8 -10.11 preloaded with 10.5 MacBook White Early 2009 5,2 iMac Early 2008 8,1; 9,1

MacBook Pro 5,1 - 6,2
early 2009

Mac Mini 3,1
early 2009

MacBook Air 2,1
Late 2008
Mac Pro 3,1 and 4,1
early 2008
10.12 & 10.13* compatible with 10.6.3 retail.  Also 10.11 compatible through 10.6.8 App Store. MacBook Late 2009 6,1 iMac Late 2009 10,1 and 11,1
10.12 & 10.13* compatible with system specific*** 10.6.3 or later MacBook 7,1 Mid 2010 iMac 11,2 Mid-2010 MacBook Pro mid-2010 7,1

Mac Mini

Mid 2010 4,1

MacBook Air Late 2010 3,1

10.12, 10.14
and
10.6.3 system specific***

Mac Pro 5,1 (2010)
10.12, 10.14, and 10.15 compatible
(original shipping OS)

MacBook early 2015 8,1
(10.10.2)

iMac Late 2012 12,1
(Shipped with 10.8.2)**
MacBook Pro Mid-2012 9,1
(10.7.3)**
Mac Mini
Late 2012 6,1
(10.8.1)**

MacBook Air Mid 2012 5,1
(10.7.4)**

Mac Pro 2013 9,1
(shipped with 10.9.1)

* Note starting with 10.13, Apple introduced APFS that made reading newer systems on older Macs that don't support Mac OS 10.13 invisible. This is especially a problem on formatted SSDs (solid state drives are drives that do not have platter based storage)
as those would automatically format in the new system.   Older platter hard drives could retain the HFS+ GUID formatting on the newer operating systems to allow older systems to see the new systems in target disk mode.
The startup manager also can "see" hard drives booting into 10.12 and earlier won't see if the Mac supports that model.

** Catalina machines that shipped with 10.8.5 or earlier need to be upgraded to 10.12 first before being able to upgrade to Catalina.   The original shipping OS, is also the OS that most likely will load when the Internet Recovery Shift-Option-⌘-R

keyboard shortcut is selected.   The cloverleaf key being the one that Apple's hardware will interpret the Windows logo key to be on a USB Windows keyboard, and the Option key is what the hardware will assume the Alt key to be.

*** System Specific disc models, had discs that are specific to the model and vintage of that model that can be used to install the operating system.  Unfortunately these Macs do not work with system restore, unless a firmware was installed first.
AppleCare may have these discs, or you might be forced to keep a clone of the original system or later system if you have to wipe or replace the drive connected to that Mac.

In Short, these skipping upgrade paths are possible if the hardware supports it:

10.6.8 -> 10.11 to 10.13

10.7.5 -> 10.12 to 10.14

10.8 -> 10.13 to 10.15