Nx586: A somewhat unusual CPU designed by NexGen -- a start up funded by unhappy Intel customers. It was fabricated by IBM. The NX586 was released in Mar 1994 as a 60 and 66MHz chip. In Sep 94 75, 80 and 90MHz versions were announced. A Nx586-120 and 133 was announced in Dec94 or Nov95 (depending on which web site you believe). The Nx586 was a RISC CPU with superscalar features that executed the Intel Instruction set. No Floating Point Unit was incorporated and it was not pin compatible with the Pentium. Despite, or perhaps because of, its odd design, the 5x86 outperformed the Intel Pentium by 15% to 50% on benchmarks that did not require extensive floating point. It's not possible to compute a rational MIPS rate based on that because of improbable Intel claims rather than implausible Nexgen claims. At a guess, MIPS for the NX586-133 are probably around 200 to 240.
The Nx586 was a 4volt CPU with a 16KB data cache and a 16KB Instruction cache. It was a 3.5 million transistor design fabricated using a .5 micron process. L2 cache used a special local bus that allowed substantially better timing than motherboard L2 caches.
NexGen was subsequently acquired by AMD which then dropped work on it's competing K5 and K6 designs and developed a new K6 design based on NexGen's planned successor to the Nx586, the Nx686.
The NX586 proved to be quite compatible with Pentium code except for the fact that software that attempted to detect the CPU type usually detected it as a 386 and sometimes refused to run programs which it was in fact perfectly capable of running.
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Copyright 1994-2002 by Donald Kenney.