The NVAX is a CMOS microprocessor developed and produced by Digital Equipment Corporation (DEC) that implemented the VAX instruction set architecture (ISA). A variant of the NVAX, the NVAX+, differed in the bus interface and external cache supported, but was otherwise identical in regards to microarchitecture. The NVAX+ was designed to have the same bus as the DECchip 21064, allowing drop-in replacement. The NVAX and NVAX+ was used in late-model VAX systems released in 1991 such as the MicroVAX 3100, VAXstation 4000, VAX 4000, VAX 6000, VAX 7000/10000 and VAXft. Although Digital updated the design throughout the early 1990s, the processors, and the VAX platform itself, were ultimately superseded by the introduction of the DECchip 21064, an implementation of the Alpha (then Alpha AXP) architecture, and the resulting systems in November 1992. The NVAX was offered at a variety of clock speeds, 83.3 MHz (12 ns), 71 MHz (14 ns) and 62.5 MHz (16 ns), while the NVAX+ is clocked at a frequency of 90.9 MHz (11 ns). The NVAX offered about 25 VAX Unit of Performance (VUPs), while the NVAX+ was roughly 35 VUPs. This was only slightly less than the VAX 9000 mainframe's roughly 40 VUPs, but available in a desktop form factor. The final model in the series was the NVAX++, or NV5, offering 50 VUPs. This was the last VAX processor, DEC had moved entirely to the DEC Alpha after that point. Description NVAX contained 1.3 million transistors on a die measuring 16.2 by 14.6 mm in size (236.52 mm²). The die was fabricated in Digital's fourth-generation CMOS process, CMOS-4, a 0.75 µm process with three layers of aluminium interconnect. The NVAX is packaged in a 339-pin pin grid array. The NVAX was offered at a variety of clock speeds, 83.3 MHz (12 ns), 71 MHz (14 ns) and 62.5 MHz (16 ns), while the NVAX+ is clocked at a frequency of 90.9 MHz (11 ns). The NVAX offered about 25 VAX Unit of Performance (VUPs). The NVAX+, introduced at the same time, was identical in terms of the processor design but used a different bus, cache system and its external connection was a 431-pin array. These were identical to those on the Alpha, allowing an NVAX+ machine to be upgraded to an Alpha simply by changing the CPU. These changes also allowed it to operate with slightly higher performance, and the NVAX+ ran at roughly