Abstract-Inspired by the function, power, and volume of the organic brain, we are developing TrueNorth, a novel modular, non-von Neumann, ultra-low power, compact architecture. TrueNorth consists of a scalable network of neurosynaptic cores, with each core containing neurons, dendrites, synapses, and axons. To set sail for TrueNorth, we developed Compass, a multi-threaded, massively parallel functional simulator and a parallel compiler that maps a network of long-distance pathways in the macaque monkey brain to TrueNorth. We demonstrate near-perfect weak scaling on a 16 rack IBM® Blue Gene®/Q (262144 CPUs, 256 TB memory), achieving an unprecedented scale of 256 million neurosynaptic cores containing 65 billion neurons and 16 trillion synapses running only 388× slower than real time with an average spiking rate of 8.1 Hz. By using emerging PGAS communication primitives, we also demonstrate 2× better real-time performance over MPI primitives on a 4 rack Blue Gene/P (16384 CPUs, 16 TB memory).I. INTRODUCTION The brain and modern computers have radically different architectures [1] suited for complementary applications. Modern computing posits a stored program model, traditionally implemented in digital, synchronous, serial, centralized, fast, hardwired, general-purpose, brittle circuits, with explicit memory addressing imposing a dichotomy between computation and data. In stark contrast, the brain uses replicated computational units of neurons and synapses implemented in mixedmode analog-digital, asynchronous, parallel, distributed, slow, reconfigurable, specialized, and fault-tolerant biological substrates, with implicit memory addressing blurring the boundary between computation and data [2]. It is therefore no surprise that one cannot emulate the function, power, volume, and realtime performance of the brain within the modern computer architecture. This task requires a radically novel architecture.Today, one must still build novel architectures in CMOS technology, which has evolved over the past half-century to serve modern computers and which is not optimized for delivering brain-like functionality in a compact, ultra-lowpower package. For example, biophysical richness of neurons and 3D physical wiring are out of the question at the very outset. We need to shift attention from neuroscientific richness that is sufficient to mathematical primitives that are necessary. A question of profound relevance to science, technology, business, government, and society is how closely can one approximate the function, power, volume, and real-time performance of the brain within the limits of modern technology.