Evolution of the Intel x86 processors in the 80s: 286, 386 and 486

Today we want to review one of the most prolific periods in its history through the evolution of the Intel x86 processors of the eighties. A time of change for personal computers.

The processor is one of the most interesting components of the PC due to its importance, history and evolution. Of all of it, few companies are more involved in all the points cited than the blue giant of semiconductors; Intel has been a constant protagonist throughout the life of this piece.

Index of contents

Seven years of continuous evolution

The period of time that we want to cover in this text dates from 1982 until the end of the eighties; During that time, processors based on the x86 architecture experienced one of the fastest and most remarkable developments in the history of modern computing and laid some of the foundations for how we understand home electronics today.

Image: Flickr; Pauli Rautakorpi

We will talk about the Intel 80286 and its implementation in the IBM PC / AT, the Intel 80386 and the rise of the PC clones through Compaq, as well as the launch and development of the Intel 80486 and the bases of what would later become Pentium. A general tour of the history of computing.

Intel 80286 (1982)

Image: Flickr; Henry Mühlpfordt

The Intel 80286 (also known as iAPX 286, or i286) is the direct successor to the Intel 80186 and 80188 processors, all belonging to the x86 family of processors, and was the CPU of choice for home PCs manufactured by IBM from launch to well into the eighties, continuing the relationship between Intel and IBM.

Some of its x86 specs

The i286 was a major leap in spec from the previous iteration of x86 processors. The P2 architecture used a 16-bit data bus (hence the categorization of the processor) and an address bus was 24-bits, a clear evolution from the original 80086. While their frequencies ranged from 4 MHz to 25 MHz in the latest revisions.

P2 architecture. Image: Wikimedia commons

Highlights include improvements in executing instructions per clock cycle and the inclusion of new instruction sets that dramatically decrease the time needed to perform some tasks; some of them needed less than twice the clock cycles to complete.

First steps in multitasking in the first x86

The i286 was characterized by the use of two modes of operation, intended for the use of multitasking applications, we are talking about protected mode and real mode.

The real mode (real address mode) was the one that came into force by default in the processor. Maintains backward compatibility with previous x86 family processors and features direct software access to the system BIOS. Thanks to this backward compatibility, i286 processors were able to use all the software developed for their predecessors, making them a very versatile processor. We highlight that it was the way in which the MS-DOS operating system and the first versions of Microsoft Windows worked.

Protected mode, on the other hand, gave the processor the ability to multitask, thanks to the ability to quickly switch two different processes. Its name derives from the limited access to the instructions of the equipment by the programs (the figure of the supervisor appears) to avoid conflicts when used together; unfortunately, this removed compatibility for much of the software, including the one named MS-DOS.

A debut by IBM

The i286 was released on IBM's third generation of personal computers, the PC / AT. The tremendous success of the New York company's system catapulted sales of the microprocessor and the establishment of the AT model as the standard in home computing encouraged the creation of software compatible with Intel's architecture.

IBM PC / AT computer. Image: wikimedia commons; MBlair Martin.

As usual at the time, Intel was not the only manufacturer. Companies like IBM itself, or the current AMD manufactured similar and compatible models, in some cases (such as that of the Harris Corporation , or AMD itself), far exceeding the speed of the original model developed by Intel.

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Intel 80386 (1985)

Image: Flickr; Contri

After the launch of the Intel 80286 would come its review, the Intel 80386 (or i386). This processor aimed to improve the features presented in the i286, adding new operating modes and numerous new features in the x86 architecture. Such was the advance that would lay the foundation for later processors, at least until the appearance of the P6 chips.

The "clones" of Intel and IBM

The original i286 was a processor designed to be produced simply and efficiently; Shortly after its original launch, and due to its success, the rest of the manufacturers began to produce and sell their own versions of the model. Some of them with substantial improvements over the original, especially in the frequencies reached.

The i386 was, at launch, an expensive processor in its production and implementation; perhaps that was the reason why IBM did not start using it until 1987, a space that the Compaq company (known for its affordable IBM compatible PCs) took advantage of to launch the Compaq Portable 386 / III to the market and take the lead in the offer. IBM PC. The golden age of clones based on the North American company's computers would begin.

Compaq PC was one of the first companies to make PCs compatible with IBM PC. Image Wikimedia Commons; Titian Garuti

Intel also did not go unpunished by other companies; That was why the i386 was not licensed for manufacturing outside of the Mountain View company's factories. However, companies like AMD and Texas Instruments continued to develop faster and more affordable i286-based processors; To combat them, Intel developed the i386SX, an inexpensive version of the original i386 with some similarities to the i286 and easier and cheaper to produce. The strategy would take effect until the early 1990s, when versions of the original i386 began to appear from AMD with the Am386 and Cyrix with their Cx486.

The powerful P3 processors

Although it would not be such a substantial jump in terms of speed as the i286, the i386 was a significant advance for the x86 processors. The frequency increased dramatically, to 12 MHz in the first models, reaching 40 MHz in later ones. The data bus was also doubled to 32-bits and the address bus was also increased to 32-bits, as well as important changes were made to the execution of instructions, and the IA-32 instruction set appeared.

P3 architecture. Image: wikimedia commons

Due to the IA-32 the compatibility with the i286 software was limited, but its implementation would lay the foundations for the x86 architecture for the next 20 years, and would influence the x86-64 instruction sets (Intel 64 for Intel) that we use in current household equipment.

On the other hand, the i386SX processors worked with a 16-bit data bus and a 24-bit address bus, making it slower, like its predecessor, although it maintained the internal design of the chip, which did count with other major improvements.

New modes, same problems on x86

Another highlight of the i386 was the implementation, again, of different functional modes. Real mode and protected mode reappeared for compatibility reasons, but a protected mode of its own made an appearance with important new features, such as the removal of segments or the virtualization of several sessions.

Unfortunately, its poor implementation continued to be the main drag on these developments; It continued to be a major limiter of the capabilities of these processors until the emergence of more advanced operating systems.

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Intel 80486 (1989)

Following the undeniable success of the i386, Intel developed the next generation of x86 processors with the goal of improving on what it had achieved with the i386. This is how the P4 processors, known worldwide as the Intel 80486, or i486 would be born.

The 387 coprocessor and the i486SX

The i486 processors are very similar to their previous generation internally, except for the integration of the 387 coprocessor; This chip included a floating point unit and unified cache within the circuit, from it monolithic chip processors would become increasingly common. Otherwise, it was still a 32-bit processor on the data bus and the address bus, and the rest of the improvements revolved more around optimizing the instruction set, or increasing frequencies, than other factors.

P4 architecture. Image: wikimedia commons

However, there was a variant of the i486, the i486SX, which dispensed with this coprocessor to cut costs. The i486SX did not have a different bus size from its original (at least by Intel), so it was a very popular chip for its lower price.

The obsession with high frequencies

What the i486 did bring was the onset of the MHz fever in processors. Intel introduced, thanks to the inclusion of the integrated cache memory, the duplication of the internal frequencies of the clock, its name was Intel OverDrive. Through them, i486 processors could operate at twice (and later triple) their frequencies for the completion of instructions, benefiting from longer ones.

The first processor with these characteristics was the i486DX2, which doubled the clock speed from 25 MHz to 50 MHz. The last iteration of this type was that of the i486DX4, tripling the frequencies to 100 MHz, although the most powerful It came from AMD with the Am5x86-P75 + that reached 150 MHz.

Supported processors re-enter and expand on x86

The similarities between the architecture of the i486 and i386 processors made things easy for manufacturers of i486-compatible processors. After the licenses disappeared with the launch of the i386, the public began to popularly refer to them as "clones", although this term only applied to those identical (internally) to the originals.

Processors derived from other brands of Intel 80486. Image: MCbx Computer Collection

One of the most prolific manufacturers of processors of this type from AMD, even going so far (as we have already mentioned) to launch more powerful models than the Intel variants, although its greatest asset in the market was still its most affordable price. That was also the Cyrix line, the result of reverse engineering of Intel processors; their processors did not perform exactly the same, so they relied on affordable prices.

Other names of interest could be IBM or Texas Instruments, although their presence was less strong than in previous stages of the x86 family of processors.

A final word about x86 processors

The x86 family processors experienced some of the most remarkable changes in their history during this time. Not surprisingly, the foundations were laid for many of the elements that would accompany us years after they came to light in these generations.

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Without a doubt, it is one of the most beautiful periods of modern computing, and the first stages of home computing as we know it today. If you want to know more about this component, we invite you to read our article on the generational leap from Intel Pentium 4 to Intel Core.