The K8 was the first implementation of the AMD64 64-bit extension to the x86 instruction set architecture.
The most radical change is the integration of the AMD64 instructions and an on-chip memory controller.
It is perceived by the PC community that after the use of the codename K8 for the Athlon 64 processor family, AMD no longer uses K-nomenclatures (which originally stood for Kryptonite[3]) since no K-nomenclature naming convention beyond K8 has appeared in official AMD documents and press releases after the beginning of 2005.
10h and 0Fh refer to the main result of the CPUID x86 processor instruction.
(The "K10h" form that sometimes pops up is an improper hybrid of the "K" code and Family identifier number.)