register memory
2.The filter in BPF was implemented by a pseudo machine, which consists of an accumulator, an index register, a scratch memory store, and an implicit program counter. BPF can be directly programmed via ioctl system call and the pseudo machine instruction set, it can also be programmed by using libpcap function library, which can access many kinds of packet capture facilities provided by OSes(BPF is the important one in them).

