The parallel branching program machine (PBM128) consists of 128 branching program machines (BMs) and a programmable interconnection. To represent logic functions on BMs, we use quaternary decision diagrams. To evaluate functions, we use 3-address quaternary branch instructions. We realized many benchmark functions on the PBM128, and compared its memory size, computation time, and power consumption with the Intel's Core2Duo microprocessor. The PBM128 requires approximately a quarter of the memory for the Core2Duo, and is 21.4-96.1 times faster than the Core2Duo. It dissipates a quarter of the power of the Core2Duo. Also, we realized packet filters such as an access controller and a firewall, and compared their performance with software on the Core2Duo. For these packet filters, the PBM128 requires approximately 17% of the memory for the Core2Duo, and is 21.3-23.7 times faster than the Core2Duo.

This paper first reviews the trends of VLSI design, focusing on the power dissipation and programmability. Then, we show the advantage of Quarternary Decision Diagrams (QDDs) in representing and evaluating logic functions. That is, we show how QDDs are used to implement QDD machines, which yield high-speed implementations. We compare QDD machines with binary decision diagram (BDD) machines, and show a speed improvement of 1.28-2.02 times when QDDs are chosen. We consider 1-and 2-address BDD machines, and 3- and 4-address QDD machines, and we show a method to minimize the number of instructions.