NEC V20/V30 were 8088/86 compatibles – now see their 8087 clone work #VintageComputing @Renesas_Japan

NEC had a cross license agreement with Intel dating back to April of 1976 that allowed each company to make/sell products based on each others patents. While producing the 8086/8088 they also began working on their own version, which would be an enhanced 8086/8088 processor. The result was the rather well known V20/V30 processors of 1984.

The V30 had some pretty big differences, notably, internally it had dual 16-bit busses, allowed data to be moved much more efficiently, as data could be moved into and out of a register at the same time (nearly).

The V30/V20 were the beginning of a line of V-series processors.  NEC went on to make  ‘186/188 style processor (the V40/V50) as well as a series of microcontroller versions  (V25/V35 and others).  The V20/V30 were to be supported by a math coprocessor like the 8087 called the upd72091.  Very little info is available on the 72091 as it was cancelled very early on in its design, as by 1984-1985 it was already out of date.  Its replacement was to be a bit more powerful.

The upd72191 was made in CMOS and is a bit like an enhanced 80C187 but with support for the V20/V30.  It is fully IEEE-754 compatible (the 8087 wasn’t as the standard wasn’t finished yet) and supports a similar instruction set as the 80C187 (and thus the 80387).  Unlike the 8087, it supports the full set of Exponential, Trig, Logarithmic, and Hyperbolic instructions.  The 8087 was somewhat limited in this, as it was already pushing the limits of what was possible on a single chip at the time of its release.

See this CPU Shack Museum article about NEC’s floating point chips, what happened and discovering a possible chip in the wild.


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