If you were around when the IBM PC rolled out, two things probably caught you by surprise. One is that the company that made the Selectric put that ridiculous keyboard on it. The other was that it had an 8-bit CPU onboard. It was actually even stranger than that. The PC sported an 8088 which was a 16-bit 8086 stripped down to an 8 bit external bus. You have to wonder what caused that, and [Steven Leibson] has a great post that explains what went down all those years ago.
Before the IBM PC, nearly all personal computers were 8-bit and had 16-bit address buses. Although 64K may have seemed enough for anyone, many realized that was going to be a brick wall fairly soon. So the answer was larger address buses and addressing modes.
The project started in 1976 but wouldn’t see the light of day until 1981. It was clear they needed something sooner, so the 8086 — a 16-bit processor clearly derived from the 8080 was born.
There were other choices, too. The Motorola 68000 was a great design, but it was expensive and not widely available when IBM was selecting a processor. TI had the TMS9900 in production, but they had bet on CPU throughput being the key to success and stuck with the same old 16-bit address bus.
That still leaves the question: why the 8088 instead of the 8086? Price. IBM had a goal to pay under $5 for a CPU and Intel couldn’t meet that price with the 8086. Apparently, it wasn’t a technical problem but a contractual one. However, folding the chip to an 8-bit external bus allowed for a smaller die, lower cost, and freedom from contractual obligations that plagued the 8086. That last point was important, as the manufacturing cost wasn’t that different, but setting the price was all about paperwork.
The IBM PC (aka the IBM 5150) had such a massive impact on computing history that origin stories about the machine are legion. Many books have been written to tell the stories of a rag-tag group of isolated engineers in IBM’s Entry Systems Business, down in Boca Raton, Florida. William C. Lowe initially led the group. He got the job after he told IBM’s Corporate Management Committee that IBM could not create a microcomputer from scratch inside the company due to fossilized thinking and corporate culture. IBM’s only hope, said Lowe, was to acquire a smaller, nimbler company to create such a machine. So naturally, IBM gave him the job of doing exactly what he said could not be done. He led the team that developed a proof-of-concept prototype in just 40 days. Don Estridge was named manager of Entry Level Systems—Small Systems–in 1980 and led the engineering team that brought the IBM PC to market in a remarkably short 12 months. IBM announced the IBM PC on August 12, 1981 and tilted the computing world on its axis.
However, that’s not today’s story. Instead, I’m going to discuss how and why IBM’s Entry Level Systems division chose the Intel 8088 microprocessor and set Intel on the path to becoming the world’s largest semiconductor manufacturer. It happened because of an intertwined series of seemingly unconnected events.
That left the Intel 8086, the stop-gap microprocessor keeping Intel’s microprocessor dynasty on life support until the magnificent iAPX 432 could be finished. The Intel 8086 had a smaller address space than either the MC68000 or the Zilog Z8000. It also delivered less performance. But it was really IBM’s only choice for a 16-bit processor, given the IBM PC’s design constraints.
There are a lot of stories that claim to explain why IBM selected an Intel 16-bit processor. Bill Gates and Paul Allen claim that Microsoft convinced IBM to pick Intel’s microprocessor. Some people have said that Regis McKenna’s Project CRUSH deserves credit for the win, but in his oral history, House says he doesn’t think there was a direct link.
“There were a number of reasons why we chose the Intel 8088 as the IBM PC’s central processor.
“1. The 64-Kbyte address limit had to be overcome. This requirement meant that we had to use a 16-bit microprocessor.
“2. The processor and its peripherals had to be available immediately. There was no time for new LSI chip development, and manufacturing lead times meant that quantities had to be available right away.
“3. We couldn’t afford a long learning period; we had to use technology we were familiar with. And we needed a rich set of support chips—we wanted a system with a DMA controller, an interrupt controller, timers, and parallel ports.
“4. There had to be both an operating system and applications software available for the processor.
“We narrowed our decision down to the Intel 8086 or 8088.”
However, IBM’s Entry Level Systems division did not pick the 8086 microprocessor for the IBM PC because IBM wanted to pay $5 for the microprocessor and Intel could not meet that price objective due to existing 8086 sales contracts with other customers. Intel really wanted to win a high-volume personal computer design and the IBM PC looked like just the thing, but those existing 8086 contracts prevented Intel from giving IBM an advantageously low price on that microprocessor. A five-buck 8086 was out of the question. Intel couldn’t put that choice on the negotiating table. The IBM PC processor pricing problem fell upon Dave House to solve.
By a happy coincidence, Intel had sent the original 8086 microprocessor design to its relatively new design facility in Haifa, Israel for a cost-reducing die shrink in 1979. In conjunction with that effort, two engineers in Haifa, Rafi Retter and Daniel (Dani) Star, converted the 8086’s 16-bit data bus into an 8-bit data bus by changing some of the bus interface unit’s circuitry and modifying some of the processor’s microcode. Because the 8086 already used a multiplexed address/data bus, the new processor’s pinout didn’t need to change from the original 8086 pinout.
Intel 8088 microprocessor was designed by Rafi Retter and Daniel Star.
“So I’m trying to get this [IBM] design win, and I’m going to lose on architecture to the 68K [Motorola’s MC68000] or the [Zilog] Z8000. So I said, where’s that 8-bit bus version?
“…we went and sold it to IBM.”
To be crystal clear, because the 8088 was not an 8086, because it was a “completely” different microprocessor with a different part number, Intel was no longer bound by the contractual price constraints on the 8086. It used the same ISA and a very similar semiconductor die, but it was a different microprocessor. Sure, the 8088’s narrower data bus throttled system performance a bit, but IBM didn’t care so much about that. After all, the PC wasn’t going to replace IBM mainframes. Price was the overriding consideration for the IBM PC.
In the final analysis, there’s clearly no significant manufacturing-cost difference between an 8086 and an 8088. They have very similar transistor counts and die sizes, and are both packaged in the same 40-pin DIP. However, there’s a price difference, and that difference won the socket. IBM didn’t particularly want a 16-bit processor with an 8-bit data bus, but if that’s what it took to get the unit price down to $5 in volume, so be it. (Further, IBM wanted a second source, so Intel engaged AMD as a second source. That AMD deal spun out its own parallel universe of fascinating stories, too numerous to even list in this article.)
In addition to the low microprocessor price, adopting the Intel 8088 gave the IBM PC design team direct compatibility with Intel’s line of low-cost, 8-bit peripheral chips (originally designed for Intel’s 8-bit microprocessors) and many of those peripheral chips ended up in the IBM PC’s system design as well. These 8-bit peripheral chips also had alternate sources, including AMD
In his oral history, House sums up the importance of the IBM PC’s introduction to Intel:
“So the IBM PC is announced, and it starts taking off, and it exceeds everybody’s expectations… And like, wow! I mean, it turns out to be the defining moment, really, for Intel.”
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4 Comments
intervento says:
Hi there, this weekend is good for me, since this occasion i am reading this impressive educational piece of writing here at my
residence.
Tomi Engdahl says:
Why the IBM PC Used an Intel 8088
Intel was inside the first personal computer, but how and why it got picked is sometimes a matter of contention.
https://au.pcmag.com/news/88771/why-the-ibm-pc-used-an-intel-8088
Tomi Engdahl says:
How The IBM PC Went 8-Bit
https://hackaday.com/2022/05/17/how-the-ibm-pc-went-8-bit/
If you were around when the IBM PC rolled out, two things probably caught you by surprise. One is that the company that made the Selectric put that ridiculous keyboard on it. The other was that it had an 8-bit CPU onboard. It was actually even stranger than that. The PC sported an 8088 which was a 16-bit 8086 stripped down to an 8 bit external bus. You have to wonder what caused that, and [Steven Leibson] has a great post that explains what went down all those years ago.
Before the IBM PC, nearly all personal computers were 8-bit and had 16-bit address buses. Although 64K may have seemed enough for anyone, many realized that was going to be a brick wall fairly soon. So the answer was larger address buses and addressing modes.
The project started in 1976 but wouldn’t see the light of day until 1981. It was clear they needed something sooner, so the 8086 — a 16-bit processor clearly derived from the 8080 was born.
There were other choices, too. The Motorola 68000 was a great design, but it was expensive and not widely available when IBM was selecting a processor. TI had the TMS9900 in production, but they had bet on CPU throughput being the key to success and stuck with the same old 16-bit address bus.
That still leaves the question: why the 8088 instead of the 8086? Price. IBM had a goal to pay under $5 for a CPU and Intel couldn’t meet that price with the 8086. Apparently, it wasn’t a technical problem but a contractual one. However, folding the chip to an 8-bit external bus allowed for a smaller die, lower cost, and freedom from contractual obligations that plagued the 8086. That last point was important, as the manufacturing cost wasn’t that different, but setting the price was all about paperwork.
Tomi Engdahl says:
How the Intel 8088 Got Its Bus
The 8086 and 8088 Helped Spark the PC Revolution and Defined Intel for Decades
https://www.eejournal.com/article/how-the-intel-8088-got-its-bus/
The IBM PC (aka the IBM 5150) had such a massive impact on computing history that origin stories about the machine are legion. Many books have been written to tell the stories of a rag-tag group of isolated engineers in IBM’s Entry Systems Business, down in Boca Raton, Florida. William C. Lowe initially led the group. He got the job after he told IBM’s Corporate Management Committee that IBM could not create a microcomputer from scratch inside the company due to fossilized thinking and corporate culture. IBM’s only hope, said Lowe, was to acquire a smaller, nimbler company to create such a machine. So naturally, IBM gave him the job of doing exactly what he said could not be done. He led the team that developed a proof-of-concept prototype in just 40 days. Don Estridge was named manager of Entry Level Systems—Small Systems–in 1980 and led the engineering team that brought the IBM PC to market in a remarkably short 12 months. IBM announced the IBM PC on August 12, 1981 and tilted the computing world on its axis.
However, that’s not today’s story. Instead, I’m going to discuss how and why IBM’s Entry Level Systems division chose the Intel 8088 microprocessor and set Intel on the path to becoming the world’s largest semiconductor manufacturer. It happened because of an intertwined series of seemingly unconnected events.
That left the Intel 8086, the stop-gap microprocessor keeping Intel’s microprocessor dynasty on life support until the magnificent iAPX 432 could be finished. The Intel 8086 had a smaller address space than either the MC68000 or the Zilog Z8000. It also delivered less performance. But it was really IBM’s only choice for a 16-bit processor, given the IBM PC’s design constraints.
There are a lot of stories that claim to explain why IBM selected an Intel 16-bit processor. Bill Gates and Paul Allen claim that Microsoft convinced IBM to pick Intel’s microprocessor. Some people have said that Regis McKenna’s Project CRUSH deserves credit for the win, but in his oral history, House says he doesn’t think there was a direct link.
“There were a number of reasons why we chose the Intel 8088 as the IBM PC’s central processor.
“1. The 64-Kbyte address limit had to be overcome. This requirement meant that we had to use a 16-bit microprocessor.
“2. The processor and its peripherals had to be available immediately. There was no time for new LSI chip development, and manufacturing lead times meant that quantities had to be available right away.
“3. We couldn’t afford a long learning period; we had to use technology we were familiar with. And we needed a rich set of support chips—we wanted a system with a DMA controller, an interrupt controller, timers, and parallel ports.
“4. There had to be both an operating system and applications software available for the processor.
“We narrowed our decision down to the Intel 8086 or 8088.”
However, IBM’s Entry Level Systems division did not pick the 8086 microprocessor for the IBM PC because IBM wanted to pay $5 for the microprocessor and Intel could not meet that price objective due to existing 8086 sales contracts with other customers. Intel really wanted to win a high-volume personal computer design and the IBM PC looked like just the thing, but those existing 8086 contracts prevented Intel from giving IBM an advantageously low price on that microprocessor. A five-buck 8086 was out of the question. Intel couldn’t put that choice on the negotiating table. The IBM PC processor pricing problem fell upon Dave House to solve.
By a happy coincidence, Intel had sent the original 8086 microprocessor design to its relatively new design facility in Haifa, Israel for a cost-reducing die shrink in 1979. In conjunction with that effort, two engineers in Haifa, Rafi Retter and Daniel (Dani) Star, converted the 8086’s 16-bit data bus into an 8-bit data bus by changing some of the bus interface unit’s circuitry and modifying some of the processor’s microcode. Because the 8086 already used a multiplexed address/data bus, the new processor’s pinout didn’t need to change from the original 8086 pinout.
Intel 8088 microprocessor was designed by Rafi Retter and Daniel Star.
“So I’m trying to get this [IBM] design win, and I’m going to lose on architecture to the 68K [Motorola’s MC68000] or the [Zilog] Z8000. So I said, where’s that 8-bit bus version?
“…we went and sold it to IBM.”
To be crystal clear, because the 8088 was not an 8086, because it was a “completely” different microprocessor with a different part number, Intel was no longer bound by the contractual price constraints on the 8086. It used the same ISA and a very similar semiconductor die, but it was a different microprocessor. Sure, the 8088’s narrower data bus throttled system performance a bit, but IBM didn’t care so much about that. After all, the PC wasn’t going to replace IBM mainframes. Price was the overriding consideration for the IBM PC.
In the final analysis, there’s clearly no significant manufacturing-cost difference between an 8086 and an 8088. They have very similar transistor counts and die sizes, and are both packaged in the same 40-pin DIP. However, there’s a price difference, and that difference won the socket. IBM didn’t particularly want a 16-bit processor with an 8-bit data bus, but if that’s what it took to get the unit price down to $5 in volume, so be it. (Further, IBM wanted a second source, so Intel engaged AMD as a second source. That AMD deal spun out its own parallel universe of fascinating stories, too numerous to even list in this article.)
In addition to the low microprocessor price, adopting the Intel 8088 gave the IBM PC design team direct compatibility with Intel’s line of low-cost, 8-bit peripheral chips (originally designed for Intel’s 8-bit microprocessors) and many of those peripheral chips ended up in the IBM PC’s system design as well. These 8-bit peripheral chips also had alternate sources, including AMD
In his oral history, House sums up the importance of the IBM PC’s introduction to Intel:
“So the IBM PC is announced, and it starts taking off, and it exceeds everybody’s expectations… And like, wow! I mean, it turns out to be the defining moment, really, for Intel.”