NexGen (Milpitas, CA) was a private semiconductor company that designed x86 PC central processing units until it was purchased by AMD in 1996. NexGen chips implemented the x86 instruction set, but were not clones of Intel's chips. They operated internally with a RISC inspired set of micro-operations, dubbed RISC86, designed solely for x86-implementation. Like competitor Cyrix, NexGen was a fabless design house that designed its chips but relied on other companies for production. NexGen's chips were produced by IBM's Microelectronics division.
Its second design, the Nx586 CPU, was introduced in 1994, was the first CPU to attempt to compete directly against Intel's Pentium, with its Nx586-P80 and Nx586-P90 CPUs. Unlike competing chips from AMD and Cyrix, the Nx586 was not pin-compatible with the Pentium or any other Intel chip and required its own custom NxVL-based motherboard and chipset. NexGen offered both a VLB and a PCI motherboard for the Nx586 chips.
Like the later Pentium-class CPUs from AMD and Cyrix, clock for clock it was more efficient than the Pentium, so the P80 ran at 75 MHz and the P90 ran at 84 MHz. Unfortunately for NexGen, it measured its performance relative to a Pentium using an early chipset; improvements included in Intel's first Triton chipset increased the Pentium's performance relative to the Nx586 and NexGen had difficulty keeping up. Unlike the Pentium, the Nx586 had no built-in math coprocessor; an optional Nx587 provided this functionality.
In later Nx586's, a x86 math coprocessor was included on-chip. Using IBM's multichip module (MCM) technology, NexGen combined the 586 and 587 die in a single package. The new device, which used the same pinout as its predecessor, was marketed as the Nx586-PF100 to distinguish it from the FPU-less Nx586-P100.
Compaq, which had backed the company financially, announced its intention to use the Nx586 and even struck the name "Pentium" from its product literature, demos, and boxes, substituting the "586" moniker, but never used NexGen's chip widely.
When AMD's K5 chip failed to meet performance and sales expectations, AMD purchased NexGen, largely to get the design team and the Nx586's follow-up design, which became the basis for the commercially successful AMD K6.