The dev_t expansion

Linux has had 16-bit device numbers since 1991
"Who needs more than 64K devices?"
This number space has gotten increasingly cramped
2.6 finally expands that space

Device numbers are now 32 bits
12 for the major number
20 for the minor number

Required changes to drivers are small
Unmodified char drivers might work 
(modulo other changes, of course)
But see new registration interface
New block interface already works