NEC V20 CPU: A bit of pep for an XT

{"@context":["https://www.w3.org/ns/activitystreams",{"Hashtag":"as:Hashtag","sensitive":"as:sensitive","dcterms":"http://purl.org/dc/terms/","gts":"https://gotosocial.org/ns#","schema":"http://schema.org/","exifData":"schema:exifData","PropertyValue":"schema:PropertyValue","interactionPolicy":{"@id":"gts:interactionPolicy","@type":"@id"},"canQuote":{"@id":"gts:canQuote","@type":"@id"},"canReply":{"@id":"gts:canReply","@type":"@id"},"canLike":{"@id":"gts:canLike","@type":"@id"},"canAnnounce":{"@id":"gts:canAnnounce","@type":"@id"},"automaticApproval":{"@id":"gts:automaticApproval","@type":"@id"},"manualApproval":{"@id":"gts:manualApproval","@type":"@id"},"always":{"@id":"gts:always","@type":"@id"},"toot":"http://joinmastodon.org/ns#","blurhash":"toot:blurhash"}],"id":"https://dfarq.homeip.net/nec-v20-cpu-a-bit-of-pep-for-an-xt/","type":"Article","attachment":[{"type":"Image","url":"https://i0.wp.com/dfarq.homeip.net/wp-content/uploads/2020/03/nec-v20-cpu.jpg?fit=720%2C409\u0026ssl=1","mediaType":"image/jpeg","name":"NEC V20"}],"attributedTo":"https://dfarq.homeip.net/author/admin/","content":"\u003Cp\u003EThe NEC V20 was an Intel 8088-compatible CPU that ran slightly faster. It was a niche CPU in the 1980s and 1990s but had a following as a cheap upgrade for power users, especially in instances where motherboard swaps were impractical. It\u0026#8217;s popular with retro computing enthusiasts today, as a \u003Ca href=\u0022https://dfarq.homeip.net/what-is-period-correctness/\u0022\u003Eperiod-correct\u003C/a\u003E upgrade. On September 22, 1986, NEC prevailed over Intel in court, clearing the way to sell it.\u003C/p\u003E\u003Cp\u003E\u003Cstrong\u003EThe NEC V20 was pin-compatible with the Intel 8088 but included some unique forward and backward compatibility features. It included the 80186 instruction set and could also emulate the Intel 8080, in addition to being faster than the 8088.\u003C/strong\u003E\u003C/p\u003E\u003Cp\u003E\u003C!--more--\u003E\u003C/p\u003E\u003Ch2\u003EThe NEC V20\u0026#8217;s slightly troubled past\u003C/h2\u003E\u003Cp\u003EIn 1982, NEC licensed the rights to produce the Intel 8088 as a second source. But in March 1984, NEC released the V20, an 8088 clone with some performance improvements. It had more than double the transistor count of the 8088 and could perform two data transfers concurrently, allowing it to complete more instructions in a given time than a real 8088.\u003C/p\u003E\u003Cp\u003EIntel sued in late 1984. NEC said the V20 was a cleanroom design. Ultimately NEC prevailed on September 22, 1986. The legal questions surrounding the V20 likely caused larger PC makers to shy away from it. By the time it was ruled legal, the market for XT-class machines was still healthy, but XTs were budget machines, so the lower transistor count of the 8088 meant a real 8088 was going to cost less in OEM quantities.\u003C/p\u003E\u003Ch2\u003EThe NEC V20 as a cheap upgrade\u003C/h2\u003E\u003Cfigure\u003E\u003Ca href=\u0022https://dfarq.homeip.net/nec-v20-cpu-a-bit-of-pep-for-an-xt/nec-v20-cpu/\u0022 rel=\u0022attachment wp-att-23246\u0022\u003E\u003Cimg src=\u0022https://i0.wp.com/dfarq.homeip.net/wp-content/uploads/2020/03/nec-v20-cpu.jpg?resize=300%2C170\u0026amp;ssl=1\u0022 alt=\u0022NEC V20\u0022 width=\u0022300\u0022 height=\u0022170\u0022 /\u003E\u003C/a\u003E\u003Cfigcaption\u003EAn NEC V20 is a cheap and easy upgrade for 8088 systems when you can\u0026#8217;t or don\u0026#8217;t want to swap a motherboard.\u003C/figcaption\u003E\u003C/figure\u003E\u003Cp\u003EThe \u003Ca href=\u0022http://www.ebay.com/sch/nec+(v20,D70108C)+(cpu,processor,microprocessor)\u0022\u003ENEC V20\u003C/a\u003E plugs directly into the Intel 8088 socket with no modifications necessary. It\u0026#8217;s slightly more efficient than an Intel 8088 running at the same clock speed. That means an NEC V20-upgraded machine performs anywhere from 8 to 30 percent faster than an 8088, depending on the application. For most applications, the improvement is around 20 percent. That\u0026#8217;s modest but may be enough to be noticeable. One place the V20 improves over the 8088 is performing multiplication and division in hardware, rather than in microcode. So it performs multiplication and division three times faster than an 8088.\u003C/p\u003E\u003Cp\u003EFor a much more technical deep dive, have a look at MartyPC\u0026#8217;s \u003Ca href=\u0022https://martypc.blogspot.com/2024/05/exploring-nec-v20-cpu.html\u0022\u003Ewriteup on the V20\u003C/a\u003E.\u003C/p\u003E\u003Cp\u003EWith Checkit 3.0, my Tandy 1000EX with an NEC V20 upgrade benchmarks 1.53x faster than the original PC/XT. In its stock configuration with a 7.16 MHz 8088, the 1000EX runs 1.31x faster than the original PC/XT.\u003C/p\u003E\u003Cp\u003EThe NEC V20 was a good processor upgrade option in machines that used nonstandard motherboards like the \u003Ca href=\u0022https://dfarq.homeip.net/ibm-pcjr-and-tandy-1000/\u0022\u003ETandy 1000 and IBM PCjr\u003C/a\u003E, and inexpensive PC/XT clones like the \u003Ca href=\u0022https://dfarq.homeip.net/leading-edge-computers/\u0022\u003ELeading Edge Model D\u003C/a\u003E. In a genuine IBM PC/XT or other clone that followed the IBM design, swapping in a small-form-factor baby AT motherboard provided more performance. But a motherboard swap cost more too.\u003C/p\u003E\u003Cp\u003EToday, replacing the 8088 in an IBM PC or XT or compatible with a NEC V20 remains a popular upgrade option. It improves performance while permitting the owner to continue using the original motherboard. Plus it\u0026#8217;s a period correct upgrade involving a vintage part from 1984. And a fair number of people in the know made the swap back then. They\u0026#8217;re easy to find on \u003Ca href=\u0022http://www.ebay.com/sch/nec+(v20,D70108C)+(cpu,processor,microprocessor)\u0022\u003Eebay\u003C/a\u003E, with prices ranging from around $10-$25 (in US dollars) depending on the vintage of the chip and the locale. The lower the price, the greater the danger of a remarked chip.\u003C/p\u003E\u003Ch3\u003ENEC V20 variants\u003C/h3\u003E\u003Cp\u003EThe NEC V20 was available at speeds of 5 MHz, 8 MHz and 16 MHz. An 8 MHz version is suitable for upgrading PC and XT machines running at 4.77 or 7.16 MHz. The 16 MHz version is suitable for 9.54 MHz turbo XT clones.\u003C/p\u003E\u003Cp\u003EThe V20 carried a part number of D70108C, so you sometimes hear it referred to by that name. NEC had three licensees who also made the chip in the 1980s. So if you find a Sharp LH70108, Sony CXQ70108, or Zilog Z70108, they are all functionally the same chip.\u003C/p\u003E\u003Cp\u003EThe V20HL is a slightly later revision that runs cooler than the original.\u003C/p\u003E\u003Cp\u003EEven though I frequently see retro computer enthusiasts on Youtube putting heatsinks on their V20s, it\u0026#8217;s not really necessary. That\u0026#8217;s especially true of the later V20HL variant. The chips run cool anyway, and in PC applications they\u0026#8217;re always running at lower than their rated speed. The heatsink doesn\u0026#8217;t hurt anything, but it\u0026#8217;s overkill.\u003C/p\u003E\u003Ch3\u003EWhat\u0026#8217;s the point?\u003C/h3\u003E\u003Cp\u003EWhen you install an NEC V20 in an \u003Ca href=\u0022https://dfarq.homeip.net/ibm-pc-introduced-august-12-1981/\u0022\u003EIBM PC 5150\u003C/a\u003E or \u003Ca href=\u0022https://dfarq.homeip.net/ibm-pc-xt-model-5160/\u0022\u003EXT 5160\u003C/a\u003E, it\u0026#8217;s still an IBM. Although a faster motherboard will fit in an XT, it\u0026#8217;s not an IBM anymore once you do that. The V20 lets you retain the original motherboard and original BIOS, everything but the CPU, and it runs a little bit faster. And if you ever need to revert the mod, it\u0026#8217;s easy. It only takes a couple of minutes to swap the 8088 back into the CPU socket.\u003C/p\u003E\u003Cp\u003EIn a PCjr or Tandy 1000, the NEC V20 gives you a slightly faster CPU to complement the machine\u0026#8217;s enhanced graphics and sound. Some of Sierra\u0026#8217;s later titles run poorly on a stock 8088 and benefit from the boost. A \u003Ca href=\u0022https://dfarq.homeip.net/tandy-1000-models#tx\u0022\u003ETandy 1000 TX\u003C/a\u003E or TL with a 286 will give better performance. But that also means you have to find one. The 8088-based Tandy 1000s were more plentiful.\u003C/p\u003E\u003Cp\u003EThe other nice thing about a NEC V20 is that some network drivers that say they require a 286 will work on a V20. If you want to network your XT-class machine to make it easier to load software on it, this is helpful.\u003C/p\u003E\u003Cp\u003EAnd if your XT motherboard is able to use a third party BIOS like \u003Ca href=\u0022https://glabios.org/\u0022\u003EGLaBIOS\u003C/a\u003E, you can get a build optimized for the V20 that uses its extra instructions to improve overall system performance.\u003C/p\u003E\u003Ch3\u003ESpeeding up your XT IDE interface\u003C/h3\u003E\u003Cp\u003EIf you have an XT IDE interface and use a compact flash card with it, installing a V20 CPU and reassembling the XT IDE BIOS with V20/80186 instructions speeds up IDE access almost 90 percent. If you use a \u003Ca href=\u0022https://dfarq.homeip.net/tandy-3-in-1-expansion-review-for-the-1000hx-and-ex/\u0022\u003ETandy 3 in 1 card\u003C/a\u003E, Rob Krenicki has already built and provided a suitable \u003Ca href=\u0022https://github.com/rkrenicki/Tandy-EX-HX-3in1/tree/main/BIOS\u0022\u003EV20 optimized BIOS\u003C/a\u003E for that purpose. On my Tandy, disk throughput went from around 250K per second to around 500K per second.\u003C/p\u003E\u003Cp\u003ESo even if the benefits when running software can be inconsistent, an NEC V20 has a very noticeable impact on your loading times, at least if you use XT IDE. And everyone likes faster loading times.\u003C/p\u003E\u003Ch2\u003EThe NEC V20 as an Intel 286 alternative\u003C/h2\u003E\u003Cp\u003EThe NEC V20 implements the Intel 80186 instruction