The HITAC S-810 is a vector supercomputer developed, manufactured and marketed by Hitachi. The first models, the S-810/10 and S-810/20, were announced in August 1982, making the S-810 was the second of the first three Japanese supercomputers, following the Fujitsu VP-200, which was announced July 1982, but predating the NEC SX-2, which was announced in April 1983. The S-810 was Hitachi's first supercomputer, although the company had previously built a vector processor, the IAP. The first system shipped was a top-end S-810/20 model, which was delivered to the University of Tokyo's Large Computer Center in October 1983. The S-810 was succeeded as Hitachi's top-end supercomputer by the HITAC S-820 announced in July 1987.
There were three models, the low-end S-810/5, the mid-range S-810/10, and the top-end S-810/20. They differ in the number of vector pipelines installed, the number of scalar registers, the number vector registers, and the amount of memory supported. Hitachi claimed that the S-810/5's peak performance was 160 MFLOPS, the S-810/10's was 315 MFLOPS, and the S-810/20's was 630 MFLOPS.
The S-810 implements a Hitachi-designed extension of the IBM System/370 instruction set architecture with 83 vector instructions (80 in the S-810/5 and S-810/10). The vector instructions are register-to-register, meaning that they do not directly reference memory. The scalar processor is a Hitachi HITAC M-280H mainframe with a 28 nanosecond (ns) cycle time (clock rate of approximately 35.71 MHz). In the S-810/20, there are 32 scalar registers, whereas the other models have 16. In all models, the scalar processor has a large 256 kilobyte cache.