How to Read Apple’s Mac OS X Build Numbers

I’m currently running Mac OS 10.5.6. This version is also known as Build 9G55. Let’s take that build number apart and see what it actually means.

Major Version Minor Version Build Update
9 G 55 b

The build refers to the Apple internal build process that does a full compile and packaging of the entire OS. The build masters use this build number to keep everything tagged properly. Version control is your friend.

The G is actually easy to understand. The first version of Mac OS 10.5 was A. So the A means 0 as in 10.5.0. Each minor revision then is the next letter of the alphabet.

0 1 2 3 4 5 6

Leopard is actually very tidy. Previous versions of Mac OS X have not been so tidy. Mac OS X 10.4.11 was build 8S2165 and 8S165 where the S and the S2 were used to distinguish between the PowerPC and Intel builds of the 11th revision of Tiger.

Why 9? This is actually the ninth version of Mac OS X. Lets review.

Version Code Name Major Version
Mac OS X 10.9 ??? 13
Mac OS X 10.8 Mountain Lion 12
Mac OS X 10.7 Lion 11
Mac OS X 10.6 Snow Leopard 10
Mac OS X 10.5 Leopard 9
Mac OS X 10.4 Tiger 8
Mac OS X 10.3 Panther 7
Mac OS X 10.2 Jaguar 6
Mac OS X 10.1 Puma 5
Mac OS X 10.0 Cheetah 4
Mac OS X Public Beta Kodiak 3
Mac OS X Server 1.0 Hera 2
Rhapsody Developer Release Grail1Z4 / Titan1U 1

When I started researching this article I expected to find a nice neat progression that would explain why Leopard is the 9th version. I thought I remembered the public beta being version 3. I now cannot find any evidence of that.It may have just been a version number of Project Builder — the predecessor of Xcode. It appears that between the Public Beta and the release of Cheetah Apple internally synchronized their internal build numbers.

The reason I assumed that version 4 made sense for Cheetah is that there were publicly released versions of Mac OS X before the Public Beta and 4 Developer Preview versions released only to developers. The public released versions were called Mac OS X Server 1.0. Released in 1999 it was little more than a port of OPENSTEP/NEXTSTEP to the G3 hardware platform. It had a “Blue Box” feature that allowed it to run Mac OS 8 applications. This Blue Box would make it into Cheetah and was a key reason for the successful transition for the Mac OS.

So to me it made sense that Mac OS X Server 1.0 was version 1. Version 2 would be Mac OS X Server 1.2. Version 3 would be the Public Beta. That gets us to version 4 for Cheetah. Unfortunately its not true. As it stands the public version numbers tell a neater progression of the versions over time than the build numbers.


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