An acquaintance recently asked me what the difference was between the NEC V20 and the Intel 186 and why the NEC V20 makes a better PC clone than an Intel 80186. The V20, after all, was compatible with the Intel 80186, but it makes for a much better PC clone. In this blog post, we will explore the NEC V20 vs Intel 80186.
Intel 186 vs NEC V20
The Intel 186 CPU was an ambitious design, integrating a number of separate formerly discrete chips, like the DMA unit, timer unit, interrupt controller unit, bus controller unit and chip select and ready generation unit, into the CPU. It wasn’t quite a system on a chip like the highly integrated CPUs in a modern phone, but it did take a couple of steps in that direction. The technology of the time didn’t permit a full SOC in a modern sense.
The problem for anyone who wanted to use a 186 in a PC was that the integrated peripheral interfaces didn’t live in the same place in memory as they do on an IBM PC. In retrospect, it seems like a questionable decision. But it’s almost certain Intel made that design decision before IBM had finalized its design for the IBM PC. The 186 CPU hit the market just a few months after the IBM PC. Intel’s timelines and IBM’s timelines just didn’t line up.
The 186 was a good CPU for its intended purpose. That purpose wasn’t making an IBM compatible computer, because that was something that didn’t exist yet.
The NEC V20 and V30 CPUs were less ambitious. They were pin-compatible, drop-in replacements for the Intel 8088 and 8086 CPUs, respectively, as well as those from Intel’s sanctioned second sources. NEC made a few tweaks to make them slightly more efficient than the original Intel design, and they added the 186 instruction set, which made them software-compatible with the 186. But from a hardware standpoint, they were compatible with the earlier generation chip.
Why the NEC V20 makes a better PC clone than an Intel 80186
The NEC V20 and V30 design meant you could take and existing design based on the 8088 or 8086, substitute a V20 or V30, and it would work. The memory layout stayed the same, the only difference was you had a CPU that was a bit more efficient and recognized a few new instructions.
Strictly speaking, the V20 and V30 weren’t 100% compatible either. If you had software that needed cycle exact timing, they glitch or fail on the NEC chip. But those were the same titles that required a turbo button on a PC clone that ran at 7.16 megahertz or faster, and those same titles also failed on 286 and later CPUs.
If you are running pre-1984 titles, some percentage of those early titles will glitch or fail on a V20 or V30. A higher percentage of those titles will glitch or fail on an Intel 80186, because the 186 adds system architecture incompatibilities on top of timing differences.
But titles that adjust for a higher clock rate generally tolerate the V20 just fine. That’s why the V20 is a popular upgrade for retrocomputing enthusiasts today, while 186-based PCs like the Tandy 2000 languished in the 80s and are mostly curiosities today.
So that’s why the NEC V20 or V30 was a better choice than the 186 for making a PC clone. The NEC designs just behaved like a slightly faster 8088 or 8086, requiring no changes to the underlying architecture. That contrasts with the 186, which did make some changes to the underlying architecture.
All that said, notably, HP used both CPUs in its 1990s palmtop PCs that ran MS-DOS.
David Farquhar is a computer security professional, entrepreneur, and author. He started his career as a part-time computer technician in 1994, worked his way up to system administrator by 1997, and has specialized in vulnerability management since 2013. He invests in real estate on the side and his hobbies include O gauge trains, baseball cards, and retro computers and video games. A University of Missouri graduate, he holds CISSP and Security+ certifications. He lives in St. Louis with his family.