Cray Research, Inc.
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Dates Used: 
Wednesday, October 1, 1986 to Sunday, September 30, 1990
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The CRAY X-MP/48 was delivered to NCAR in October 1986, replacing NCAR's second CRAY-1A, S/N 14. The cost of the computer was $14.6 million, plus $3.5 million for the 256-megaword (2 gigabyte) Solid State Disk and $2 million for the disks.

The power and cooling infrastructure for the underground computing room at the NCAR Mesa Laboratory was expanded to provide the necessary physical facilities for the new computer. The computer electrical power and grounding systems were replaced, and the cooling system piping (which provided a backup chilled-water source in the event of a failure) was redesigned.

The X-MP/48 featured a new multiprocessor architecture, housing four processors in one cabinet. This opened the door to parallel execution of models, allowing models to be partitioned into a number of asynchronously executable parts. This mode of use, called multitasking, was not extensively used, but was the harbinger of modern-day parallel computing.

Each X-MP processor could execute an instruction in 8.5 nanoseconds and had a peak computation rate of 235 million floating-point operations per second (megaflops).  NCAR's X-MP had a main memory of eight million 64-bit words (64 megabytes). The processors were significantly faster than those for the CRAY-1A, and could communicate with each other extremely efficiently.

From an historical perspective, with the installation of the Cray X-MP, computing performance at NCAR had improved about 430 times since 1963, while system cost had only increased by about a factor of 6.

The X-MP/48 increased the computing capability available to NCAR users by approximately threefold. Each processor delivered about 500 CPU hours of computer time each month to users. While the system was capable of a peak computation rate of 941 megaflops, the average sustained rate on NCAR's workload was 225 megaflops; that is, approximately 25% of peak.  It was the vector capabilities of the Cray processors combined with a memory subsystem which could stream data to and from the processors at processor-clock speeds which allowed NCAR applications to achieive such a high percentage of the system's peak processing rate.

An Input/Output Subsystem (IOS), which had first been introduced on larger models of the Cray-1S systems, was an integral part of the X-MP. The IOS accumulated input data for the central processor and distributed output data, which freed the X-MP's CPUs from time-consuming peripheral activities and provided connectivity with a variety of equipment provided other vendors (e.g., CDC, IBM, VAX, Sun).

As with NCAR's two Cray-1A's, NCAR's X-MP ran the Cray Operating System (COS) from Cray Research, Inc.  Other X-MPs ran the Cray Time-Sharing System (CTSS), which was jointly developed by Los Alamos and Lawrence Livermore National Laboratories, or UNICOS, developed by Cray Research, Inc., which was based on AT&T's UNIX System V technology. The X-MP was the last supercomputer to run an operating system that was not based in some manner on UNIX, from which today's ubiquitous Linux operating system was derived.

NCAR's CRAY X-MP/48 was decommissioned on September 30, 1990, four months after the CRAY Y-MP8/864, which NCAR named shavano, arrived.