Science Fair Project Encyclopedia
The Cray X-MP was a supercomputer designed, built and sold by Cray Research. The company's first parallel vector processor machine and a fourth generation super, it was the 1982 successor to the 1976 Cray-1, and the world's fastest computer 1983–1985.
The principal designer was Steve Chen. The X-MP shared the 'horseshoe' design of the earlier machine. The processors ran on an 10 nanosecond clock (compared to 12.5 ns for the Cray-1A), delivering a theoretical peak speed of 200 megaflops per processor and 800 megaflops for the four processor 1982 machine. The processors also had better chaining support, parallel arithmetic pipes, and shared memory access with multiple pipelines per processor.
The system initially ran the proprietary Cray Operating System (COS), with UniCOS (a UNIX System V derivation) running through the guest operating system facility. UniCOS became the main OS from 1984 onwards.
The X-MP was sold with one, two, or four processors and from one to sixteen megawords (8–128 MB) of word addressable RAM main memory (while initial memory capacity was limited to 16 megawords with a 24-bit address register, the later extended memory architecture XMP/EA raised addressable memory to a theoretical 2 GigaWords, in practice the largest memory produced was 64 MegaWords. The XMP/EA had a 8.5 nanosecond clock), delivering a theoretical peak speed of 942 megaflops. A 1982 X-MP/48 was about US$15 million plus the cost of disks.
The Cray-2, a completely new design, was introduced 1985. A very different compact four-processor design with from 512 MB to 4 GB of main memory, it was clocked at 500 megaflops but was slower than the X-MP on certain calculations due to its high memory latency. In 1986 an X-MP/48 achieved a speed of 713 megaflops on the standardized LINPACK tests.
The X-MP-succeeding Cray Y-MP series was sold from 1988; no radical design, it was an evolutionary improvement of the X-MP with a new processor and the capacity for up to sixteen.
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