The Good Olde Days

Even-numbered kernels were 'stable'
1.0, 1.2, 2.0, 2.2, 2.4

Odd-numbered kernels were 'development'
1.1, 1.3, 2.1, 2.3, 2.5...

The cycle worked like this:
Start a new development series
Feed in patches for some time
Freeze features, only accept fixes
Wait for things to stabilize
Release a new stable series
Start over