In recent years, many commercial Massively Parallel Processor (MPP) systems have been available available to the computing community. These systems provide very high processing power (up to hundreds of GFLOPs), and can scale efficiently with the number of processors. However, many scientific and commercial applications that run on these multiprocessors may not experience significant benefit in terms of speedup and are bottlenecked by their I/O requirements. Although these multiprocessors may be configured with sufficient I/O hardware, the file system software often fails to provide the available I/O bandwidth to the application, and causes severe performance performance degradation for I/O intensive applications.A highly efficient parallel file system has been implemented on Intel's Teraflops (TFLOPS) machine and provides a sustained I/O bandwidth of 1 GB/sec. This file system provides almost 95% of the available raw hardware I/O bandwidth and the I/O bandwidth scales proportional to the available I/O nodes.Intel's TFLOPS machine is the first Accelerated Strategic Computing Initiative (ASCI) machine that DOE has acquired. This computer is 10 times more powerful than the fastest machine today, and will be used primarily to simulate nuclear testing and to ensure the safety and effectiveness of the nation's nuclear weapons stockpile.This machine contains over 9000 Intel's Pentium Pro processors, and will provide a peak CPU performance of 1.8 teraflops. This papers presents the I/O design and architecture of Intel's TFLOPS supercomputer, describes the Cougar OS I/O and its interface with the Intel's Parallel File System.