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Computer History 101: The Development Of The PC

The IBM Personal Computer

At the end of 1980, IBM decided to truly compete in the rapidly growing low-cost personal computer market. The company established the Entry Systems Division, located in Boca Raton, Florida, to develop the new system. The division was intentionally located far away from IBM’s main head­quarters in New York, or any other IBM facilities, so that it would be able to operate independently as a separate unit. This small group consisted of 12 engineers and designers under the direction of Don Estridge and was charged with developing IBM’s first real PC. (IBM considered the previous 5100 system, developed in 1975, to be an intelligent programmable terminal rather than a genuine computer, even though it truly was a computer.) Nearly all these engineers had come to the new division from the System/23 DataMaster project, which was a small office computer system introduced in 1980 and the direct predecessor of the IBM PC.

Enter The First PC-Compatible System, Using Intel's 8088 CPU

Much of the PC’s design was influenced by the DataMaster design. In the DataMaster’s single-piece design, the display and keyboard were integrated into the unit. Because these features were limiting, they became external units on the PC, although the PC keyboard layout and electrical designs were copied from the DataMaster.

Several other parts of the IBM PC system also were copied from the DataMaster, including the expansion bus (or input/output slots), which included not only the same physical 62-pin connector, but also almost identical pin specifications. This copying of the bus design was possible because the PC used the same interrupt controller as the DataMaster and a similar direct memory access (DMA) controller. Also, expansion cards already designed for the DataMaster could easily be redesigned to function in the PC.

The DataMaster used an Intel 8085 CPU, which had a 64 KB address limit and an 8-bit internal and external data bus. This arrangement prompted the PC design team to use the Intel 8088 CPU, which offered a much larger (1 MB) memory address limit and an internal 16-bit data bus, but only an 8-bit external data bus. The 8-bit external data bus and similar instruction set enabled the 8088 to be easily interfaced into the earlier DataMaster designs.

IBM brought its system from idea to delivery of functioning systems in one year by using existing designs and purchasing as many components as possible from outside vendors. The Entry Systems Division was granted autonomy from IBM’s other divisions and could tap resources outside the company, rather than go through the bureaucratic procedures that required exclusive use of IBM resources. IBM contracted out the PC’s languages and OS to a small company named Microsoft. That decision was the major factor in establishing Microsoft as the dominant force in PC software.

Digital Research Makes Way For Microsoft

It is interesting to note that IBM had originally contacted Digital Research (the company that created CP/M, then the most popular personal computer OS) to have it develop an OS for the new IBM PC. However, Digital was leery of working with IBM and especially balked at the nondisclosure agreement IBM wanted Digital to sign. Microsoft jumped on the opportunity left open by Digital Research and, consequently, became the largest software company in the world. IBM’s use of outside vendors in developing the PC was an open invitation for the after-market to jump in and support the ­system—and it did.

On August 12, 1981, a new standard was established in the microcomputer industry with the debut of the IBM PC. Since then, hundreds of millions of PC-compatible systems have been sold, as the original PC has grown into an enormous family of computers and peripherals. More software has been written for this computer family than for any other system on the market.

The PC Industry 30 Years Later

In the 30 years since the original IBM PC was introduced, many changes have occurred. The IBM-compatible computer, for example, advanced from a 4.77 MHz 8088-based system to 3 GHz (3000MHz) or faster systems—about 100 000 or more times faster than the original IBM PC (in actual processing speed, not just clock speed). The original PC had only one or two single-sided floppy drives that stored 160 KB each using DOS 1.0, whereas modern systems can have several terabytes (trillion bytes) or more of hard disk storage.

A rule of thumb in the computer industry (called Moore’s Law, originally set forth by Intel cofounder Gordon Moore) is that available processor performance and disk-storage capacity doubles every one and a half to two years, give or take.

Since the beginning of the PC industry, this pattern has held steady and, if anything, seems to be accelerating.

Moore’s Law

In 1965, Gordon Moore was preparing a speech about the growth trends in computer memory and made an interesting observation. When he began to graph the data, he realized a striking trend existed. Each new chip contained roughly twice as much capacity as its predecessor, and each chip was released within 18–24 months of the previous chip. If this trend continued, he reasoned, computing power would rise exponentially over relatively brief periods.

Moore’s observation, now known as Moore’s Law, described a trend that has continued to this day and is still remarkably accurate. It was found to not only describe memory chips, but also accurately describe the growth of processor power and disk drive storage capacity. It has become the basis for many industry performance forecasts. As an example, in less than 40 years the number of transistors on a processor chip increased more than half a million fold, from 2300 transistors in the 4004 processor in 1971 to 1.17 billion transistors in the six-core versions of the Core i-series processors released in 2010.

The PC-Compatible Open Standard

In addition to performance and storage capacity, another major change since the original IBM PC was introduced is that IBM is not the only manufacturer of PC-compatible systems. IBM originated the PC-compatible standard, of course, but today it no longer sets the standards for the system it originated. More often than not, new standards in the PC industry are developed by companies and organizations other than IBM.

Today, Intel, Microsoft, and AMD are primarily responsible for developing and extending the PC hardware and software standards. Some have even taken to calling PCs “Wintel” systems, owing to the dominance of the first two companies. Although AMD originally produced Intel processors under license and later produced low-cost, pin-compatible counterparts to Intel’s 486 and Pentium processors (AMD 486, K5/K6), starting with the Athlon AMD has created completely unique processors that are worthy rivals to Intel’s own models.

In more recent years, the introduction of hardware standards such as the universal serial bus (USB), Peripheral Component Interconnect (PCI) bus, Accelerated Graphics Port (AGP) bus, PCI Express bus, ATX motherboard form factor, as well as processor socket and slot interfaces show that Intel is the ­driving force behind PC hardware design. Intel’s ability to design and produce motherboard chipsets as well as complete motherboards has enabled Intel processor–based systems to first adopt newer memory and bus architectures as well as system form factors. Although in the past AMD has on occasion made chipsets for its own processors, the company’s acquisition of ATI has allowed it to become more aggressive in the chipset marketplace.

PC-compatible systems have thrived not only because compatible hardware can be assembled easily, but also because the most popular OS was available not from IBM but from a third party (Microsoft). The core of the system software is the basic input/output system (BIOS); this was also available from third-party companies, such as AMI, Phoenix, and others. This situation enabled other manufacturers to license the OS and BIOS software and sell their own compatible systems. The fact that DOS borrowed the functionality and user interface from both CP/M and UNIX probably had a lot to do with the amount of software that became available. Later, with the success of Windows, even more reasons would exist for software developers to write programs for PC-compatible systems.

The Apple Macintosh Closed Standard

One reason Apple’s Macintosh systems have never enjoyed the market success of PC systems is that Apple has often used proprietary hardware and software designs that it was unwilling to license to other companies. This proprietary nature has unfortunately relegated Apple to a meager 5% market share in personal computers.

One fortunate development for Mac enthusiasts was Apple’s shift to Intel x86 processors and PC architecture in 2006, resulting in greatly improved performance and standardization as compared to the previous non-PC-compatible Mac systems. Although Apple has failed to adopt some of the industry-standard component form factors used in PCs (rendering major components such as motherboards noninterchangeable), the PC-based Macs truly are PCs from a hardware standpoint, using all the same processors, chipsets, memory, buses, and other system architectures that PCs have been using for years. I’ve had people ask me, “Is there a book like Upgrading and Repairing PCs that covers Macs instead?” Well, since 2006 Macs have essentially become PCs, they are now covered in this book by default! The move to a PC-based architecture is without a doubt the smartest move Apple has made in years—besides reducing Apple’s component costs, it allows Macs to finally perform on par with PCs.

Apple could even become a real contender in the OS arena (taking market share from Microsoft) if the company would only sell its OS in an unlocked version that would run on non-Apple PCs. Unfortunately for now, even though Apple’s OS X operating system is designed to run on PC hardware, it is coded to check for a security chip found only on Apple motherboards. There are ways to work around the check (see, but Apple does not support them.

Apple’s shift to a PC-based architecture is one more indication of just how popular the PC has become. After 30 years the PC continues to thrive and prosper. With far-reaching industry support and an architecture that is continuously evolving, I would say it is a safe bet that PC-compatible systems will continue to dominate the personal computer marketplace for the foreseeable future.

  • raclimja

    i still have my pentium 2 gathering dust on my closet

    improvements in technology is AMAZING
  • grooveboss
    ^ dweeb alert
  • Pyree
    The article contains no post-PC era nonsense! Just the way it should be.
  • dogman_1234
    I liked it. Love history; and the history of computerized technology. Can't wait to see the next 50 years.
  • mayankleoboy1
    just one question:

    why this article? in the whole wide range of PC, why this?
    you could have done the second part to the Antiliasing article.
  • cangelini
    mayankleoboy1just one question: why this article? in the whole wide range of PC, why this?you could have done the second part to the Antiliasing article.
    That's still on its way. It's very data-intensive and Don has been plugging away at it.
  • Chewie
    No mention of the Commodore in any of its forms? :(
  • SteelCity1981
    2006: Microsoft releases the long-awaited Windows Vista to business users. The PC OEM and consumer market releases would follow in early 2007:

    It should really read.

    2006: Microsoft releases the long-awaited Windows Vista to business users. The PC OEM and consumer market releases would follow in early 2007 and the vast majority of people quickly downgraded back to Windows XP:

  • madsbs
    Pics or it didn't happen!

    Where are the illustrations for this rather interesting piece?
  • jj463rd
    One thing that I disliked about the Timeline of Computer Advancements was leaving out Douglas Englebart and the Mother of All Demos in 1968(if you don't know about him you know very little about computer history )and giving accolades instead to Xerox.