The history of the processor is an interesting one, full of fierce competition and advanced technology, yet short in the terms of years. At the point where I will begin addressing this history, we are beginning with a 5 MHz 8086 processor, and today we are routinely seeing 1.8 GHz to up over 2 GHz. What a difference 20-some years can make. Let us start.
In the Beginning, there was 8086…
CPUs have gone through many changes through the few years since Intel came out with the first one. IBM chose Intel’s 8088 processor for the brains of the first PC. This choice by IBM is what made Intel the perceived leader of the CPU market. Intel remains the perceived leader of microprocessor development. While newer contenders have developed their own technologies for their own processors, Intel continues to remain more than a viable source of new technology in this market, with the ever-growing AMD nipping at their heels.
The first four generations of Intel processor took on the „8“ as the series name, which is why the technical types refer to this family of chips as the 8088, 8086, and 80186. This goes right on up to the 80486, or simply the 486. The following chips are considered the dinosaurs of the computer world. PC’s based on these processors are the kind that usually sit around in the garage or warehouse collecting dust. They are not of much use anymore, but us geeks don’t like throwing them out because they still work. You know who you are.
• Intel 8086 (1978)
This chip was skipped over for the original PC, but was used in a few later computers that didn’t amount to much. It was a true 16-bit processor and talked with its cards via a 16 wire data connection. The chip contained 29,000 transistors and 20 address lines that gave it the ability to talk with up to 1 MB of RAM. What is interesting is that the designers of the time never suspected anyone would ever need more than 1 MB of RAM. The chip was available in 5, 6,, 8, and 10 MHz versions.
• Intel 8088 (1979)
The 8088 is, for all practical purposes, identical to the 8086. The only difference is that it handles its address lines differently than the 8086. This chip was the one that was chosen for the first IBM PC, and like the 8086, it is able to work with the 8087 math coprocessor chip.
• NEC V20 and V30 (1981)
Clones of the 8088 and 8086. They are supposed to be about 30% faster than the Intel ones, though.
• Intel 80186 (1980)
The 186 was a popular chip. Many versions have been developed in its history. Buyers could choose from CHMOS or HMOS, 8-bit or 16-bit versions, depending on what they needed. A CHMOS chip could run at twice the clock speed and at one fourth the power of the HMOS chip. In 1990, Intel came out with the Enhanced 186 family. They all shared a common core design. They had a 1-micron core design and ran at about 25MHz at 3 volts. The 80186 contained a high level of integration, with the system controller, interrupt controller, DMA controller and timing circuitry right on the CPU. Despite this, the 186 never found itself in a personal computer.
• Intel 80286 (1982)
A 16-bit, 134,000 transistor processor capable of addressing up to 16 MB of RAM. In addition to the increased physical memory support, this chip is able to work with virtual memory, thereby allowing much for expandability. The 286 was the first „real“ processor. It introduced the concept of protected mode. This is the ability to multitask, having different programs run separately but at the same time. This ability was not taken advantage of by DOS, but future Operating Systems, such as Windows, could play with this new feature. On the the drawbacks of this ability, though, was that while it could switch from real mode to protected mode (real mode was intended to make it backwards compatible with the 8088’s), it could not switch back to real mode without a warm reboot. This chip was used by IBM in its Advanced Technology PC/AT and was used in a lot of IBM-compatibles. It ran at 8, 10, and 12.5 MHz, but later editions of the chip ran as high as 20 MHz. While these chips are considered paperweights today, they were rather revolutionary for the time period.
• Intel 386 (1985 – 1990)
The 386 signified a major increase in technology from Intel. The 386 was a 32-bit processor, meaning its data throughput was immediately twice that of the 286. Containing 275,000 transistors, the 80386DX processor came in 16, 20, 25, and 33 MHz versions. The 32-bit address bus allowed the chip to work with a full 4 GB of RAM and a staggering 64 TB of virtual memory. In addition, the 386 was the first chip to use instruction pipelining, which allows the processor to start working on the next instruction before the previous one is complete. While the chip could run in both real and protected mode (like the 286), it could also run in virtual real mode, allowing several reasl mode sessions to be run at a time. A multi-tasking operating system such as Windows was necessary to do this, though. In 1988, Intel released the 386SX, which was basically a low-fat version of the 386. It used the 16-bit data bus rather than the 32-bit, and it was slower, but it thus used less power and thus enabled Intel to promote the chip into desktops and even portables. In 1990, Intel released the 80386SL, which was basically an 855,00 transistor version of the 386SX processor, with ISA compatibility and power management circuitry.
386 chips were designed to be user friendly. All chips
in the family were pin-for-pin compatible and they were binary compatible with the previous 186 chips, meaning that users didn’t have to get new software to use it. Also, the 386 offered power friendly features such as low voltage requirements and System Management Mode (SMM) which could power down various components to save power. Overall, this chip was a big step for chip development. It set the standard that many later chips would follow. It offered a simple design which developers could easily design for.
Intel 486 (1989 – 1994)
The 80486DX was released in 1989. It was a 32-bit processor containing 1.2 million transistors. It had the same memory capacity as the 386 (both were 32-bit) but offered twice the speed at 26.9 million instructions per second (MIPS) at 33 MHz. There are some improvements here, though, beyond just speed. The 486 was the first to have an integrated floating point unit (FPU) to replace the normally separate math coprocessor (not all flavors of the 486 had this, though). It also contained an integrated 8 KB on-die cache. This increases speed by using the instruction pipelining to predict the next instructions and then storing them in the cache. Then, when the processor needs that data, it pulls it out of the cache rather than using the necessary overhead to access the external memory. Also, the 486 came in 5 volt and 3 volt versions, allowing flexibility for desktops and laptops.
The 486 chip was the first processor from Intel that was designed to be upgradeable. Previous processors were not designed this way, so when the processor became obsolete, the entire motherboard needed to be replaced. With the 486, the same CPU socket could accommodate several different flavors of the 486. Initial 486 offerings were designed to be able to be upgraded using „OverDrive“ technology. This means you can insert a chip with a faster internal clock into the existing system. Not all 486 systems could use OverDrive, since it takes a certain type of motherboard to support it.
The first member of the 486 family was the i486DX, but in 1991 they released the 486SX and 486DX/50. Both chips were basically the same, except that the 486SX version had the math coprocessor disabled (yes, it was there, just turned off). The 486SX was, of course, slower than its DX cousin, but the resulting reduced cost and power lent itself to faster sales and movement into the laptop market. The 486DX/50 was simply a 50MHz version of the original 486. The DX could not support future OverDrives while the SX processor could.
In 1992, Intel released the next wave of 486’s making use of OverDrive technology. The first models were the i486DX2/50 and i486DX2/66. The extra „2“ in the names indicate that the normal clock speed of the processor is being effectively doubled using OverDrive, so the 486DX2/50 is a 25MHz chip being doubled to 50MHz. The slower base speed allowed the chip to work with existing motherboard designs, but allowed the chip internally to operate at the increased speed, thereby increasing performance.
Also in 1992, Intel put out the 486SL. It was virtually identical to vintage 486 processors, but it contained 1.4 million transistors. The extra innards were used by its internal power management circuitry, optimizing it for mobile use. From there, Intel released various 486 flavors, mixing SL’s with SX’s and DX’s at a variety of clock speeds. By 1994, they were rounding out their continued development of the 486 family with the DX4 Overdrive processors. While you might think these were 4X clock quadruplers, they were actually 3X triplers, allowing a 33 MHz processor to operate internally at 100 MHz.
AM486DX Series (1994 – 1995)
Intel was not the only manufacturer playing in the sandbox at the time. AMD put out its AM486 series in answer to Intel’s counterpart. AMD released the chip in AM486DX4/75, AM486DX4/100, and AM486DX4/120 versions. It contained on-board cache, power management features, 3-volt operation and SMM mode. This made the chip fitting for mobiles in addition to desktops. The chip found its way into many 486-compatibles.
AMD AM5x86 (1995)
This is the chip that put AMD onto the map as official Intel competition. While I am mentioning it here on the 486 page of the history lesson, it was actually AMD’s competitive response to Intel’s Pentium-class processor. Users of the Intel 486 processor, in order to get Pentium-class performance, had to make use of an expensive OverDrive processor or ditch their motherboard in favor of a true Pentium board. AMD saw an opening here, and the AM5x86 was designed to offer Pentium-class performance while operating on a standard 486 motherboard.. They did this by designing the 5×86 to run at 133MHz by clock-quadrupling a 33 MHz chip. This 33 MHz bus allowed it to work on 486 boards. This speed also allowed it to support the 33 MHz PCI bus. The chip also had 16 KB on-die cache. All of this together, and the 5×86 performed better than a Pentium-75. The chip became the de facto upgrade for 486 users who did not want to ditch their 486-based PCs yet.
The Pentium (1993)
By this time, the Intel 486 was entrenched into the market. Also, people were used to the traditional 80×86 naming scheme. Intel was busy working on its next generation of processor. It was not to be called the 80586, though. There were some legal issues surrounding the ability for Intel to trademark the numbers 80586. So, instead, Intel changed the name of the processor to the
a name they could easily trademark. They released the Pentium in 1993. The original Pentium performed at 60 MHz and 100 MIPS. Also called the „P5“ or „P54“, the chip contained 3.21 million transistors and worked on the 32-bit address bus (same as the 486). It has a 64-bit external data bus which could operate at roughly twice the speed of the 486.
The Pentium family includes the 60/66/75/90/100/120/133/150/166/200 MHz clock speeds. The original 60/66 MHz versions operated on the Socket 4 setup, while all of the remaining versions operated on the Socket 7 boards. Some of the chips (75MHz – 133MHz) could operate on Socket 5 boards as well. Pentium is compatible with all of the older operating systems including DOS, Windows 3.1, Unix, and OS/2. Its superscalar design can execute two instructions per clock cycle. The two separate 8K caches (code cache and data cache) and the pipelined floating point unit increase its performance beyond the x86 chips. It had the SL power management features of the i486SL, but the capability was much improved. It has 273 pins that connect it to the motherboard. Internally, though, its really two 32-bit chips chained together that split the work. The first Pentium chips operated at 5 volts and thus operated rather hotly. Starting at the 100MHz version, the requirement was reduced to 3.3 volts. Starting at the 75MHz version, the chip also supported Symmetric Dual Processing, meaning you could use two Pentiums side by side in the same system.
The Pentium stayed around a long time. It was released in many different speeds as well as different flavors. In fact, Intel implemented an „s-spec“ rating which is marked on each Pentium CPU which tells the owner some key data about the processor in order to make sure they have their motherboard set correctly. There were just so many different Pentiums out there that it became hard to tell. You can look up processor specs using the s-spec at the link below.
Related Link: Intel Processor Spec Finder
The Pentium Pro (1995-1999)
If the regular Pentium is an ape, this processor evolved into being human. The Pentium Pro (also called „P6“ or „PPro“) is a RISC chip with a 486 hardware emulator on it, running at 200 MHz or below. Several techniques are used by this chip to produce more performance than its predecessors. Increased speed is achieved by dividing processing into more stages, and more work is done within each clock cycle. Three instructions can be decoded in each clock cycle, as opposed to only two for the Pentium. In addition, instruction decoding and execution are decoupled, meaning that instructions can still be executed if one pipeline stops (such as when one instruction is waiting for data from memory; the Pentium would stop all processing at this point). Instructions are sometimes executed out of order, that is, not necessarily as written down in the program, but rather when information is available, although they won’t be much out of sequence; just enough to make things run smoother. Such improvements to the PPro resulted in a chip optimized for higher end desktop workstations and network servers.