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A Brief History of Computers in General, and the Personal Computer in Particular

The development of computers over the last few decades has been very rapid. While there are better sources out there for examining any aspect of the computer revolution in detail, this page provides a very brief overview of some of the major milestones in computing history to provide some historical perspective.

Aids to Calculation

Since the dawn of civilization, people have had to do arithmetic, and it was an irksome and error-prone task.

In Mesopotamia, an early form of the abacus was in use in 2300 BC or earlier; in several cultures, the abacus was in use by 600 to 200 BC.

Napier's first publication describing logarithms and their use as an aid to calculation dates from 1614; William Oughtred invented the slide rule in 1622, which made their use for multiplication to limited precision convenient.

The first mechanical adding machines were invented by Pascal and Schickard in 1642.

Early Automatic Digital Computers

The first attempt at what we think of today as a computer, based on mechanical calculator technology, was, of course, the Analytical Engine by Charles Babbage, first described in 1837.

While that project may seem so impractical that it could not have avoided its eventual failure even under more favorable circumstances, the same cannot be said of the later project of his contemporary, Torres y Quevedo, who envisaged building an electrical computer using relays. Torres y Quevedo is best known for the demonstration machine he built to generate interest in, and raise money for, his computer project, a machine that could play a simple Chess endgame, first demonstrated in 1914.

Analog Computers

In the 1950s and early 1960s, popular works on the computer would often note that there were two fundamental kinds of computer, the digital computer and the analog computer. Today, when we think of computers, we generally only think of digital computers, because they can do all sorts of fun and exciting things.

Analog computers, like slide rules, are limited in the precision of the numbers they work with. They were used to solve complicated equations which would have been too expensive to solve more precisely on the digital computers available at the time.

A famous mechanical analog computer was the Differential Analyzer, constructed by Vannevar Bush starting in 1927. It makes a brief cameo in the movie "When Worlds Collide". One key component involved a wheel that was driven by a rotating disk; as the wheel could be moved do different positions on the disk, changing the effective gear ratio (somewhat the way some automatic transmissions work) it was used to calculate the integral of a function.

In the 1950s and early 1960s, electronic analog computers which connected operational amplifiers and other electronic components together with patch cords were commercially available.

The Beginnings of the Computer Era

The Harvard Mark I, conceived in 1939, used a program on a punched paper tape to control calculations performed with electromechanical relays. It became operational in 1944. As initially designed, it did not have a conditional branch instruction. Howard Aiken, its designer, referred to it as "Babbage's dream come true", which shows that Charles Babbage's work did not get rediscovered after the computer age was in full swing, as has occasionally been claimed.

The ENIAC was the first well-known fully electronic computer. Its completion was announced on February 14, 1946, after having been secretly constructed during World War II. It was originally programmed through plugging patch cords.

One of its components was an array of dials in which a table of values for a function to be used could be set up; John von Neumann developed a patch cord program that let the machine execute a program entered on those dials. This reduced the speed of the machine's computations, but it drastically shortened the amount of time it took to set the machine up for work on a different problem.

Soon afterwards, many computers were developed that used vacuum tubes to calculate electronically that were much smaller than ENIAC, based on the stored-program concept that John von Neumann had pioneered. Some were still large, like the Univac I, and some were small, like the Bendix G-15.

Von Neumann himself planned to go on from his work on the ENIAC to create a computer designed around the stored program concept, the EDVAC. As it happened, a British group based at the University of Cambridge was the first to complete a computer based on the EDVAC design, the EDSAC, in May, 1949; the month after, the Manchester Mark I was completed: however, a year before, in June, 1948, the Manchester group had a prototype machine working, giving them the honor of building the world's first stored-program electronic computer.

At first, one of the major problems facing computer designers was finding a way to store programs and data for rapid retrieval at reasonable cost. Recirculating memories, taken from devices originally invented for radar systems, such as mercury delay lines and magnetostrictive delay lines, were used, along with drum memories and their equivalent, head-per-track disks. A special cathode ray tube that stored what was displayed on its face for later readout, called a Williams Tube, provided some of the earliest random-access memories, but it was not as reliable as was desired in practice.

The Univac I and the DEUCE used mercury delay lines, the Bendix G-15 had a drum, the Ferranti Mercury used magnetostrictive delay lines, and the Maniac I and the IBM 701 used Williams tubes.

The magnetic core memory, used in the Whirlwind computer prototype, the AN/FSQ-7 computer used for air defense, and the commercial IBM 704 scientific computer, allowed computers to be built that were, in many important respects, not all that different from the computers we use today.

The IBM 704 computer was introduced in 1954. It performed single-precision arithmetic in hardware; as well, its single-precision floating-point arithmetic instructions retained additional information, normally generated in the course of performing addition, subtraction, or multiplication, that allowed programs to perform double-precision arithmetic to be short and efficient.

IBM developed the first FORTRAN compiler for the IBM 704. Higher-level languages existed before FORTRAN, but because this compiler was designed to generate highly optimized code, it overcame the major objection to higher-level languages, that they would be wasteful of valuable computer time.

Transistors replaced vacuum tubes, and then integrated circuits replaced discrete transistors.

Another major computer milestone took place on April 7, 1964, when IBM announced their System/360 line of computers.

These computers used microprogramming to allow the same instruction set, and thus the same software, to be used across a series of machines with a broad range of capabilities. The Model 75 performed 32-bit integer arithmetic and floating-point arithmetic, both single and double precision, directly in hardware; the Model 30 had an internal arithmetic-logic unit that was only 8 bits wide.

By this time, IBM was already the dominant computer company in the world. The IBM 704, and its transistorized successors such as the IBM 7090, helped to give it that status, and the IBM 1401, a smaller transistorized computer intended for commercial accounting work, was extremely successful in the marketplace.

The System/360 was named after the 360 degrees in a circle; the floating-point instructions, and commercial instructions to handle packed decimal quantities, were both optional features, while the basic instruction set worked with binary integers; so the machine was, and was specifically advertised as, suitable for installations with either scientific or commercial workloads. And because the related features were options, it was not necessary for one kind of customer to pay extra to be able to handle the other kind of work. Well, in theory; in practice, other brands of computer tended to be much cheaper than those from IBM, but IBM provided very reliable computers with excellent customer support.

IBM invented the vacuum column which significantly improved the performance of magnetic tape drives for computers; their 1403 line printer was legendary for its print quality and reliability; and they invented the hard disk for the RAMAC vacuum-tube computer from 1956.

As a consequence of IBM's major presence in the computer industry, their computers were very influential. Before the IBM System/360, nearly all computers that worked with binary numbers (many instead worked with decimal numbers only) had a word length (the size of numbers they worked with) that was a multiple of six bits. This was because a six bit character could encode the 26 letters of the alphabet, 10 digits, and an adequate number of punctuation marks and special symbols.

The IBM Systm/360 used an eight-bit byte as its fundamental unit of storage. This let it store decimal numbers in packed decimal format, four bits per digit, instead of storing them as six bit printable characters (like the IBM 705 and the IBM 1401 computers, for example).

To clarify: some decimal-only computers like the IBM 7070 and the NORC, also by IBM, and the LARC from Univac, had already been using packed decimal; and the Datamatic 1000 by Honeywell, a vacuum-tube computer with a 48-bit word, used both binary and packed decimal long before the System/360 came along.

So I'm not saying that IBM invented the idea of using no more bits than necessary for storing decimal numbers in a computer; that was obvious all along. Rather, what I'm trying to say is that IBM's desire to use this existing technique led them to choose a larger size for storing printable characters in the computer. This larger size made it possible to use upper and lower case with the computer, although lower case was still initially regarded as a luxury, and it was not supported by most peripheral equipment.

In 1969, a later implementation of the System/360, the System/360 Model 195, combined cache memory, introduced on the large-scale microprogrammed 360/85 computer, and pipelining with reservation stations using the Tomasulo algorithm, equivalent to out-of-order execution with register renaming, introduced on the 360/91 (and used on both the 91 and the 195 only in the floating-point unit). This was a degree of architectural sophistication that would only be seen in the mainstream of personal computing with microprocessors when the Pentium II came out.

Simple pipelining, where fetch, decode, and execute of successive instructions was overlapped, had been in use for quite some time; splitting the execute phase of instructions into parts would only be useful in practice if successive instructions didn't depend on one another. The IBM STRETCH computer from 1961 attempted such pipelining, and was a disappointment for IBM. The Control Data 6600 computer, a computer built from discrete transistors from 1965, on the other hand, was a success; it used a technique called "scoreboarding" which was a simpler form of out-of-order execution.

This is not to say it is defective; the need for register renaming can be avoided simply by using a larger register file - the IBM 360 had four floating-point registers, while RISC processors typically have banks of at least 32 registers. The scoreboard of the Control Data 6600 is eminently suitable for dealing with the remaining use case for out-of-order execution that a larger register file can't solve, cache misses.

That is not to say the CDC 6600 had a cache; it explicitly transferred data from a slower large memory to its smaller main memory with specialized instructions. One advantage it had in providing high performance with a simple design was that it was a new design from scratch, whereas IBM sought to provide high performance and strict compatibility with their existing System/360 line of mainframes, which is what made both the Tomasulo algorithm and cache memory necessities for them.


The year 1976 was marked by the installation of the first Cray I computer. A few years previously, there were a couple of other computers, such as the STAR-100 from Control Data and the Advanced Scientific Computer from Texas Instruments, that directly operated on one-dimensional arrays of numbers, or vectors. The earlier machines, because they performed calculations only on vectors in memory, only provided enhanced performance on those specialized where the vectors could be quite long. The Cray I had a set of eight vector registers, each of which had room for 64 double-precision floating-point numbers 64 bits in length, and, as well, attention was paid to ensuring it had high performance in those parts of calculations that worked with individual numbers.

As a result, the Cray I was very succesful, sparking reports that the supercomputer era had begun. A few years later, not only did several other companies offer computers of similar design, some considerably smaller and less expensive than the supercomputers from Cray, for users with smaller workloads, but as well add-on units, also resembling the Cray I in their design, were made to provide vector processing with existing large to mid-range computers. IBM offered a Vector Facility for their 3090 mainframe, starting in October 1985, and later for some of their other large mainframes, based on the same principles; Univac offered the Integrated Scientific Processor for the Univac 1100/90; and the Digital Equipment Corporation offered a Vector Processor for their VAX 6000 and VAX 9000 computers, also patterned after the Cray design.

Another line of development relating to vector calculations on a smaller scale may be noted here.

The AN/FSQ-7 computer, produced by IBM for air defense purposes, performed calculations on two 16-bit numbers at once, rather than on one number of whatever length at a time like other computers, to improve its performance in tracking the geographical location of aircraft. This vacuum tube computer was delivered in 1958.

Two computers planned as successors to it offered more flexibility. The AN/FSQ-31 and AN/FSQ-32 computers, dating from around 1959, had a 48 bit word, and their arithmetic unit was designed so that it could perform arithmetic on single 48-bit numbers or pairs of 24-bit numbers; and the TX-2 computer, completed in 1958, could divide its 36-bit word into two 18-bit numbers, four 9-bit numbers, or even one 27-bit number and one 9-bit number.

In 1997, Intel introduced its MMX feature for the Pentium microprocessor which divided a 64-bit word into two 32-bit numbers, four 16-bit numbers, or eight 8-bit numbers.

This was the event that brought this type of vector calculation back to general awareness, but before Intel, Hewlett-Packard provided a vector extension of this type, MAX, for its PA-RISC processors in 1994, and Sun provided VIS for its SPARC processors in 1995.

Since then, this type of vector calculation has been extended beyond what the TX-2 offered; with AltiVec for the PowerPC architecture, and SSE (Streaming SIMD Extensions) from Intel, words of 128 bits or longer are divided not only into multiple integers, but also into multiple floating-point numbers.

In January, 2015, IBM announced that its upcoming z13 mainframes, since delivered, would include vector instructions; these were also of this type, now common on microcomputers, as opposed to the more powerful Cray-style vector operations offered in 1985.

It may be noted that IBM introduced its z/Architecture in the year 2000; this extension of the System/360 mainframe architecture provided 64-bit addressing. The first machine on which it was implemented was the z/900. The z/900 was announced in October, 2000, and was to be available in December, 2000.

The 64-bit Itanium from Intel only became available in June, 2001, and the first chips from AMD that implemented the x64 extension to the 80386 architecture, that Intel later adopted as EM64T, were shipped in April, 2003.

However, AMD had releasd the x64 spec in 1999, and this was after Intel had described the Itanium, as it was a reaction to Intel's way of moving to 64 bits.

Thus it seemed that the microprocessor beat the mainframe to 64-bit addressing, but the 64-bit z/Architecture mainframe was delivered first.

However, there are other microprocessors besides those which are compatible with the Intel 80386. The Alpha microprocessor was introduced in 1992, and Sun adapted its SPARC architecture to 64-bit addressing in 1995, so IBM was anticipated by microprocessors used in servers and high-end workstations.

The Minicomputer Revolution

A transistorized computer, the PDP-1, was first delivered to Bolt, Beranek, and Newman in November, 1960, made by an up-and-coming computer company, the Digital Equipment Corporation. It had an 18-bit word. Another specimen of this model was sold to MIT, and some students there occasionally used it to play Spacewar.

The next model of computer sold by DEC was the PDP-4. It also had an 18 bit word, but it was not compatible with the PDP-1. It had a simpler design; for example, the opcode field in each instruction was five bits long in the PDP-1, but four bits long in the PDP-4, so the latter had about half as many instructions that involved working with data at an address in memory. The instruction set was even more constrained because it included two versions of most binary arithmetic instructions, one that used one's complement arithmetic and one that used two's complement arithmetic.

They then made an even simpler computer, initially envisaged for industrial process control applications, although from the start it was suitable for general-purpose use, the PDP-5. This computer had a word length of only 12 bits. It used memory location 0 to store its program counter.

They later made a large-scale computer, the PDP-6, with a 36-bit word and hardware floating-point, and a new model of computer compatible with the PDP-4, the PDP-7.

And then DEC made history with the PDP-8 computer. In a small configuration, it could sit on a table top, despite still being made from discrete transistors. It was similar to the PDP-5, but with one minor incompatibility; it had a real program counter, and so it moved the interrupt save locations one position earlier in memory. This was not a serious problem, as few PDP-5 computers were sold, and only a limited amount of software was developed for them.

The original PDP-8 sold for $18,000. It was introduced on March 22, 1965. It is considered to have begun the era of minicomputers. There were computers before that weren't giant mainframes that filled whole rooms; the Bendix G-15 filled one corner of a room, being a bit larger than a refrigerator, despite being made with vacuum tubes; the Recomp II was a box that sat on the floor beside a desk, being about as high as the desk and half as wide.

In 1961, the Packard-Bell pb205 computer was not that much bulkier than a PDP-8 would later be. However, to make it affordable, it used magnetostrictive delay lines instead of core as memory; by then, most computers did use core memory, and unwillingness to give up the convenience that offered may have limited its success. Also, the price was $40,000.

The later PDP-8/S, announced on August 23, 1966, set new milestones in the minicomputer era. It sold for under $10,000, and it could be delivered from stock. And it was much more compact than the original PDP-8. However, it achieved its low cost by using much slower core memory, and a serial arithmetic unit, so its lesser performance limited its popularity.

DEC then implemented this architecture with integrated circuits, providing two models, the full-featured PDP-8/I, and the less-expensive PDP-8/L for which some options were not available for expansion.

A revised integrated-circuit model included some modifications to the optional feature, the Extended Arithmetic Element, which provided hardware multiplication. This was the PDP-8/e. Introduced in the summer of 1970, its price was initially $6,500, and that price was later reduced to $4,995. DEC encouraged its sale to schools and colleges. Before there were microcomputers, a group called the "People's Computer Company" encouraged individuals to attempt to purchase one if they could afford it; they had a magazine that featured game programs written in BASIC.

Other companies besides DEC made minicomputers.

The Honeywell 316 computer, first made available in 1969, was a minicomputer that followed in the architectural tradition of the Computer Control Company (3c) DDP-116 from 1964; the Hewlett Packard 2116, from 1967, was the first in a line of minicomputers from that company. Both of these computers had 16 bit words; their basic architecture was similar to that of the PDP-8, the PDP-4, or the PDP-1, in that instructions did calculations between an accumulator and one memory location, the memory location was indicated by a short address which included one bit to indicate whether it referred to a location on the same page of memory as the current instruction or a location on the globally shared page zero of memory, and there was also an indirect bit in instructions to allow these short addresses to point to an address that took up a whole word (whether of 12, 16, or 18 bits) to allow broader access to memory. Some of the larger computers of this group also had an index register, and a bit to indicate if its contents would be added to the address before use.

When DEC decided to make its own minicomputer in the popular 16 bit word length, however, rather than designing something similar to the Honeywell 316 and the Hewlett-Packard 2114 with the PDP-8 and the PDP-4 as sources of inspiration, it did something quite different.

The first PDP-11/20 computers were delivered in the spring of 1970.

This computer's instruction word consisted of a four-bit opcode field, followed by two operand fields, each six bits long, consisting of three bits to indicate an addressing mode, and three bits to indicate a register.

If the addressing mode for either or both operands was indexed addressing, for each operand in that mode, a sixteen-bit address was appended to the instruction. The register field was used to indicate a register to use as an index register for the instruction.

So instructions could be 16, 32, or 48 bits in length, and they could be register-to-register, memory-to-register, register-to-memory, or memory-to-memory.

This was more than a little reminiscent of the IBM System/360 computer.

In one important respect, however, the PDP-11 was very unlike the System/360. The System/360 included instructions that worked with packed decimal numbers, and instructions to convert directly between them and character strings. So decimal and binary numbers in memory were organized the same way strings of digits in text were organized - with the most significant part in the lowest memory address. This is known as the "big-endian" numeric representation.

The Honeywell 316 computer, as one example, had instructions to perform a 32-bit two's complement binary addition. It was not as fancy as a System/360 mainframe, and so to make things simple, it picked up the least significant 16 bits of a 32-bit number from one word, then performing that part of the addition and saving the carry for later use, and then picked up the most significant bits of the 32-bit number from the next word.

It addressed memory as 16-bit words, not as 8-bit bytes. When character data was packed into 16-bit words, the first of two characters would be in the left, or most significant, half of the word.

So if you put the character string "ABCD" into such a computer, and read it out as a 32-bit integer, that integer would be composed of the ASCII codes for the letters in this order: C, D, A, and B. At the time, this was not much of a concern, but it seemed inelegant.

The PDP-11 addressed memory in 8-bit bytes, as the IBM System/360 did. But it, too, was a small minicomputer intended to be much cheaper than the IBM System/360. So, like the Honeywell 316, when it worked with 32-bit integers, it put the least significant 16-bit word first, and the most significant 16-bit word second.

How to be as beautifully consistent as the System/360, instead of messy like the Honeywell 316?

Well, while much later packed decimal and string hardware became available as options for larger PDP-11 models, it didn't start out with them. So the idea came to them: why not, when packing two characters of text in a 16-bit word, place the first character in the least significant half of the word? And so give that byte the lower address, since here individual bytes were addressable.

So now the ASCII codes for "ABCD" would be found in a 32-bit number in the order D, C, B, and A, which was at least systematic.

The PDP-11 originated the idea of making a computer that was consistently little-endian. A floating-point hardware option made for it, however, put the most significant portions of floating-point numbers in words with lower addresses, thus marring that consistency. But it is still the PDP-11 that inspired many later designs, particularly microprocessors such as the Intel 8008, 8080, 8086, 80386, and so on, the MOS Technology 6502, and the National Semiconductor 16032 to be little-endian. In contrast, the Texas Instruments 9900, as well as the Motorola 6800 and 68000, were big-endian.

The Microcomputer Revolution

In accordance with Moore's Law, as time went on, it became possible to put more transistors on a single chip and make it do more things.

So when once people were suitably amazed that one could get four NAND gates on a single chip, it became possible to put 64 bits of high speed memory on one chip, or a four-bit wide arithmetic-logic unit on one chip.

That something weird and wonderful was in the wind had perhaps already been apparent for some time when something happened to make it unmistakably obvious, on the first day of February in 1972. That was the day when Hewlett-Packard announced the HP-35 pocket calculator.

It fit in your pocket and ran on batteries. It calculated trignometric functions and logarithms to ten places of accuracy. And it cost $395.

In 1974, however, the Texas Instruments SR-50 came out, for only $170, and you didn't have to learn RPN to use it.

Shortly after, though, you could get a scientific calculator for as little as $25. One such calculator was the Microlith scientific (model 205, though that was just in small print on the back). It only calculated to 8 digit accuracy, with trig and log functions calculated only to 6 digits. It used a green vacuum fluorescent display instead of LEDs.

If a single chip could calculate log and trig functions, it ought to be possible for a single chip to perform just basic arithmetic along with control functions to step through a program, which would not seem to be more complicated. However, memory was still expensive; as well, speed wasn't a critical issue in a pocket calculator, which could do its calculations one decimal digit at a time.

Hewlett-Packard didn't sit on its laurels, though; even as other companies came out with much cheaper rivals to the HP-35, they came out with the HP-65. Not only was it programmable - including with conditional branch instructions - but it could save programs on small magnetic cards.

Two years later, in November 1976, the Texas Instruments SR-52 came out as a cheaper rival; however, it was a bit too fat to fit in most pockets, although you wouldn't know it from the photos in the advertisements. It wasn't until the TI-59 came out in 1977 that Texas Instruments had a magnetic card calculator that was sufficiently svelte to conform to the common notion of what constituted a pocket calculator.

Before the HP-35, there had been electronic calculators that could sit on top of a desk for some time. The Hewlett-Packard 9100A, available in 1968, was a programmable scientific calculator of relatively compact size and impressive capabilities; among its competitors were the Wang 500 calculator from 1971 and the Monroe 1655 (among several different models with different capabilities) from 1970. Wang Laboratories sold the LOCI-2 programmable electronic calculator as early as 1965.

Over this same time frame, the microcomputer revolution was starting.

The cover of the July 1974 issue of Radio-Electronics magazine showed a computer you could build at home! It was the Mark 8, based on the Intel 8008 microprocessor.

The Intel 8008 fit in an 18-pin package, as small as that containing many ordinary integrated circuits. It used a single 8-bit bus for data and (in two parts) addresses. As there were two status bits included with the most significant byte of the address, it could only be connected to a maximum of 16K bytes of memory, not 64K, although at the time memory was too expensive for this to be much of a limitation. Initially, however, the support chips for the 8008 were in limited supply.

This, though, did not make much of a splash at the time.

The same was not the case, though, with the January 1975 issue of Popular Electronics. That was the one that had the Altair 8800 on the cover, based on the Intel 8080 chip. This chip was in a 40-pin package, a size in which many other 8-bit microprocessors were also packaged. It had a full 16-bit address bus along with an 8-bit data bus.

Magazines hit store shelves before their printed cover dates; according to Wikipedia, this magazine was distributed in November 1974. That can be said to be when the microcomputer revolution started in earnest.

The pace of events from then on was rapid.

December 1976 marks the first shipment of the Processor Technology SOL-20 computer. It was designed to be easier to use than an Altair or an IMSAI (a clone of the Altair, built to a higher standard of production quality); instead of a box with lights and switches, it had a keyboard in it, and hooked up to a video monitor. The regulatory hurdles to including an RF modulator for use with one's TV set hadn't quite been sorted out at that time just yet.

It was moderately popular with early adopters. However, it was in the next year that the floodgates opened, as 1977 was the year of the original Commodore PET computer, the first Radio Shack TRS-80, and the Apple II.

This was also the year when North Star offered a 5 1/4" floppy disk drive system, admittedly one using more expensive and harder-to-find hard-sectored floppy disks, for S-100 bus computers. It included North Star DOS, a simple operating system with two-letter commands.

By the time the IBM Personal Computer was announced on August 12, 1981, various brands of 8080 and Z-80 based computer running the CP/M operating system were well established in the market. But the IBM Personal Computer, although not fully compatible with them, was very similar - although offering the possibility of expanding main memory to one megabyte instead of being limited to 64K bytes (although some CP/M based systems used external circuitry to allow up to 128K bytes of memory to be used). This possibility of expansion, plus the prestige of the IBM name - and this didn't just mean their reputation for quality; while many systems using the same CP/M operating system were made by different manufacturers, they weren't fully compatible with each other, and so this meant standardization, a convenient and competitive market for third-party software - made the IBM Personal Computer an immediate success.

July 1982 is when the Timex-Sinclair 1000 computer was introduced, a home computer for those of modest means. For the less impecunious, the Atari 400 in 1979, the Commodore VIC-20 and the Radio Shack Color Computer in 1980, and the Commodore 64 came out in January 1982.

1984 is memorable for two advances. In that year, IBM brought out a larger model of their personal computer, the IBM Personal Computer AT, which used the more powerful 80286 processor. A far more influential event, though, was the introduction by Apple of the Macintosh computer.

The Apple Lisa computer had been introduced in January, 1983. Like the Macintosh, it had a graphical user interface, so when the Macintosh came out, it did not come as a total shock. The Macintosh, however, was far less expensive, and was thus something home users could consider.

In 1985, Compaq brought out the Compaq Deskpro 386, which used Intel's new 386 microprocessor. This computer was faster and more powerful than an IBM Personal Computer AT, and with appropriate software, it could make use of more memory. Of course, it was expensive, but as the years went by, prices of systems based on the 80386 chip came down; as well, a compatible chip with a 16-bit external bus, the 80386SX, was offered by Intel starting in 1985, which allowed more affordable systems to use the capabilities that the 80386 offered over the 80286.

In April, 1992, Microsoft offered version 3.1 of their Microsoft Windows software to the world. This allowed people to use their existing 80386-based computers compatible with the standard set by the IBM Personal Computer to enjoy a graphical user interface similar to that of the Macintosh, if not quite as elegant, at a far lower price.

That is not to say that nothing happened between 1984 and 1992. July 1985 marked the availability of the Atari ST computer, and in early 1986 one could get one's hands on an Amiga 1000. So there were GUI alternatives cheaper than a Macintosh before 1992, but this was one that just involved buying software for the computer you already had, the computer that was the standard everyone else was using for serious business purposes.

In 1989, the Intel 80486 chip came out; unlike previous chips, it included full floating-point software as a standard feature right on the chip, although later the pin-compatible 80486SX was offered at a lower price without floating-point.

In 1993, Intel offered the first Pentium chips, available in two versions, the full 66 MHz version, and a less expensive 60 MHz version. These chips were criticized for dissipating a considerable amount of heat, and there was the unfortunate issue of the floating-point division bug.

The Intel Pentium Pro chip was announced on November 1, 1995. This design was optimized for 32-bit software, and was criticized for its performance with the 16-bit software that most people were still using. The later Pentium II resolved that issue, but was otherwise largely the same design, but of course with improvements. Further improvements appeared in the Pentium III.

The Pentium 4 chip was a completely new design. It had fewer gate delays per pipeline stage. This meant that the chip's cycle frequency was faster, but instructions took more cycles to execute. At the time, this sounded to people like it was a marketing gimmick instead of an improvement. In fact, though, it was a real improvement, because the Pentium 4 was a pipelined chip with out-of-order execution, intended to issue new instructions in every single cycle, rather than waiting to perform one instruction after another.

But initially it required the use of a new and more expensive form of memory, which did not help its success in the market.

Intel's subsequent chips in the Core microarchitecture went back to many aspects of the Pentium III design for an important technical reason: shorter pipeline stages meant that the transistors on the chip were doing something a greater fraction of the time. This would produce more heat, and the characteristics of newer, smaller integrated circuit processes were not proving as favorable as hoped (this is known as the demise of Dennard scaling), and so a similar design on a newer process would have dissipated more heat than it would be practical to remove.

And, thus, other means of increasing performance were needed, and we entered the era of dual-core and quad-core microprocessors.

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