This is the only technique provided for many RISC processors, but CISC architectures such as x86 support additional techniques. For example, the x86 instruction set contains the instructions codice_14/codice_15 and codice_16/codice_17 (these two mechanisms were independently created by AMD and Intel, respectively, but in essence they do the same thing). These are "fast" control transfer instructions that are designed to quickly transfer control to the kernel for a system call without the overhead of an interrupt. Linux 2.5 began using this on the x86, where available; formerly it used the codice_18 instruction, where the system call number was placed in the codice_19 register before interrupt 0x80 was executed.