The CRAY X-MP/48 was delivered to NCAR in October 1986, replacing the second CRAY-1A. The basic cost of the computer was $14.6 million, plus $3.5 million for the 256-megaword Solid State Disk and $2 million for the disks.
The underground computing room at the 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 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 pointed the way to parallel computing.
Each X-MP processor could execute an instruction in 8.5 nanoseconds and had a main memory of eight million 64-bit words. The processors were significantly faster than those for the CRAY-1, and could communicate with each other extremely efficiently. (In fact, 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. The average actual rate of calculations at NCAR was 55 megaflops per processor (220 megaflops for the whole computer).
An Input/Output Subsystem (IOS), which had first been introduced on larger models of CRAY-1S systems and proved its worth, was an integral part of the X-MP. The IOS accumulated input for the central processor and distributed output, which freed the CPU from time-consuming peripheral activities and provided connectivity with a variety of other vendor equipment (e.g., CDC, IBM, VAX, Sun).
The X-MP supported the Cray Operating System (COS), the Cray Time-Sharing System (CTSS), and UNICOS, which was based on UNIX System V technology.
The CRAY X-MP/48 was decommissioned on September 30, 1990, four months after the CRAY Y-MP8/864 arrived.