50 Years of computer architecture: From the mainframe CPU to the domain-specific tpu and the open RISC-V instruction set

IBM had four incompatible computer lines. Each had its own unique instruction-set architecture (ISA); I/O system; system software (assemblers, compilers, libraries); and market niches (business, scientific, real time). IBM engineers bet that they could invent a single ISA that would work for customers of all four lines. Moreover, the same program would run correctly on any implementation of that ISA, though at different speed and cost. That vision required a new way to build computers that would be binary compatible from the cheapest 8-bit model to the fastest 64-bit version.