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The PC at 20 - An Upgrader's Perspective

The PC at 20 - An Upgrader's Perspective

20 years ago, on August 12, 1981, IBM's Personal Systems division in Boca Raton, Florida rolled out the IBM Personal Computer Model 5150, a system better known as the original IBM PC.

While it wasn't the first "personal computer" (many credit the 1975 MITS Altair as the first), it was the first "PC", where PC means a class of personal computers that are compatible with each other. Today, PCs account for approximately 95% of the personal computer market.

The original IBM PC's modular, expandable design spawned a whole industry of compatible hardware and software to follow, making PCs the defacto standard personal computers used by most people around the world. The systems we call "PCs" today are really just compatible evolutionary descendants of the original IBM PC system. It is a testament to the standardization of the PC that amazingly almost all of the operating systems and software (and much of the hardware) designed for the first IBM PCs in 1981 still function on a modern PC today!

On the 20th anniversary of this computing revolution, it's useful to see how the design of the IBM PC not only established a new dominant species among personal computers, but also made upgrading and inexpensive repairing possible, and how it continues to affect our upgrade and repair possibilities today.

Open Architecture - Then

The IBM PC broke with other personal-computing pioneers by providing an open, expandable architecture. Rather than insisting upon making sure that every component inside the IBM PC was a custom component created internally, IBM, unlike the competition, made extensive use of off-the-shelf components. Starting with the motherboard, the main processor and virtually all of the supporting chips came from Intel. Because IBM was nervous about having a single supplier for these components, they required that Intel license the chips to other companies, such as AMD, NEC and Harris. So, for example, a disaster at an Intel chip plant wouldn't put IBM out of the PC business. IBM's forcing their major suppliers to license their technology was one of the central reasons that made the PC what it is today, and helped to foster competition among the suppliers that has kept options open and prices down to this day. AMD got their start in the PC processor business because Intel licensed them to make exact copies of the early Intel processors, all thanks to IBM.

For disk interfaces IBM sought pre-existing standards rather than develop custom solutions such as those that Apple had been known for. The floppy disk drives used the standard Shugart SA-400 interface and came from companies like Shugart, Tandon, and Control Data. Hard drives used the standard Seagate ST-506/412 interface and came from companies like Seagate, MiniScribe, and IMI.

This use of standard interfaces and components carried on to peripherals as well. The PC was available with industry standard RS-232 serial interfaces as well as the parallel printer interface that Centronics self-named and developed. The first IBM printers were actually modified Epson dot-matrix printers

IBM published detailed documentation and schematic circuit diagrams for their systems, and even included full source code listings of their BIOS, which allowed developers to create add-in boards. Soon multi-function cards from companies like Quadram and AST began to replace the inefficient one-function, one-card design of a stock IBM PC, which had only a single slot to perform all types of I/O.

Open Architecture - Now

The interior of a PC today is different in detail than on the early IBM PCs. PCI and AGP slots have replaced 8/16-bit ISA slots, motherboard and power supply form factors have changed, and drives are much smaller in form factor, while also much larger in capacity. Despite all that, the open-architecture philosophy still reigns supreme.

Attempts to put a proprietary flair on the PC architecture, such as the IBM MicroChannel bus equipped PS/2s of the late 1980's and early 1990's have flopped, and deservedly so. The same holds true for the LPX-based systems produced by companies such as Packard-Bell. Today's systems are largely based on industry-standard form factors like ATX, Micro-ATX and NLX. So, just as in the pioneering PC days, you can replace practically everything from the power supply to the motherboard and improve your system dramatically in the process. And, thanks to IBM's demand on Intel and others to provide alternative sources for their components, companies like AMD began to develop the expertise that has led to the highly competitive Athlon and Duron processors.

BIOS Limitations - Then

It wasn't long before the first PCs required upgrades to the BIOS to either correct bugs or add new features. While it took more than a decade to develop the field-upgradable flash memory BIOS chips common today, periodic BIOS chip upgrades for PC, PC-XT, AT, and clone/compatible systems became an occasional annoyance for many users during the 1980's and early '90's. These upgrades required opening the system, as well as the removal and replacement of the socketed BIOS chip.

BIOS Limitations - Today

The pace of technology change has accelerated, as have the need for BIOS upgrades. Fortunately, it's increasingly rare to need to physically replace the BIOS chip on today's systems, but many users will perform at least one downloadable BIOS upgrade during the life of their systems. While the packaging and location of the BIOS chip has changed, the ability to upgrade the firmware that enables the system to cope with newer devices and software is another legacy of the IBM PC.

The open architecture of the IBM PC, and the division of management tasks between the BIOS and the operating system also made it possible for 3rd-party BIOS vendors like Phoenix, Award (now part of Phoenix), and AMI to engineer work-alike BIOSes with more features. These BIOSes are found inside the vast majority of new systems today, even those from major vendors such as Gateway, Dell, MicronPC and others.

Power and Drive Upgrades - Then

The original 5-slot IBM PC had a physically huge but appallingly underpowered 63.5-watt power supply. The 8-slot, hard-drive version (the IBM PC/XT) had a less-underpowered 130-watt power supply. Thanks to open architecture, it didn't take long for third-party vendors to build better, more powerful power supplies to replace the original units, providing the power needed for cards in every slot and drives in every bay.

Similarly, the IBM PC's original 160/180KB single-sided floppy drives were quickly replaced by double-sided 320/360KB models, and the original 10MB hard disks by larger 20MB, 30MB, and even 40MB models. The IBM PC and PC/XT's motherboard had no built-in I/O controllers except for a keyboard, everything from the floppy controller to the hard disk controller, as well as serial/parallel and even mouse ports all had to be added via plug-in cards. The original PC and XT didn't even have a clock, and there was no CMOS RAM either, the system configuration was entirely controlled by dip switches on the board. Several vendors sold clock cards (often combined as part of a multifunction card) which included their own software to set the date and time in the operating system.

The original IBM PC and PC/XT provided users with a choice between tack-sharp green text (but no graphics) or "colorful" 4-color CGA graphics and fuzzy text. Even in the early days of the PC, 3rd-party vendors like Hercules put sharp text and graphics together for green-screen users, and IBM eventually developed better video standards such as EGA and today's baseline, VGA.

Power and Drive Upgrades - Today

Today's PC vendors, with few exceptions, are still up to their old tricks when it comes to power supplies, drives, and video: installing the smallest and cheapest components that get the systems out the door.

Fortunately, bigger, faster, better replacements for power supplies, drives, and video cards are just a purchase and a screwdriver away. Again, while the details of the PC have changed over time, the open architecture of the PC standard that IBM created has continued into today's models, giving you the ability to change anything you like.

Operating Systems = Then

When their first PC was being developed in 1980-81, IBM had a choice between the established (Digital Research's CP/M) or something entirely. IBM chose Microsoft, then famous primarily for its version of BASIC, to provide an operating system. Microsoft licensed Seattle Computer Products' "quick-and-dirty" operating system (which looked and felt a lot like CP/M) and turned it into MS-DOS. IBM called their version PC-DOS, but didn't prevent Microsoft from selling it to other computer vendors under the MS-DOS name.

Operating Systems - Today

Love Microsoft or hate it, if IBM had prevented Microsoft from selling MS-DOS to other vendors, the PC business today would be as closed today as the Apple Macintosh systems are. There wouldn't be the choice in system manufacturers, components, and even software that we have today. Had IBM not allowed Microsoft to license, and had Apple seen the light and licenced their system, we would all be using their systems today. The de facto standard status of PC-DOS/MS-DOS helped provide a common basis for software, even as IBM, along with Intel processors and chipsets provided a common hardware basis.

While Microsoft Windows has become, in the eyes of some, a dangerous monopoly, the open architecture and common standards of the PC world is making it easier for potential rivals such as Linux to have a chance at nibbling away at Microsoft's dominance. Administrators of Linux-based Apache web servers, for example, haven't had to worry about the proliferation of attacks such as RedWorm and RedWorm 2 against the Internet, since Microsoft's servers are much more vulnerable.


While increasingly low-cost PCs integrate sound, video, and even modem and network functions into the motherboard, and reduce slot count, the open architecture design that the IBM PC inspired continues to make upgrading possible and desirable. From the least expensive "home" computer to a fire-breathing gamer's dream, any PC user can still replace everything from the keyboard to the motherboard and get a better system, a task that simply can't be done to the same extent with Apple or any other hardware platform. Thank you, IBM, for creating an open architecture PC!

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