The PC Turns 30

Yesterday, August 12, was the 30th anniversary of the introduction of the IBM Model 5150 Personal Computer.  It was by no means the first computer for individual customers; the Apple II was available, along with machines from Commodore and Atari, and a variety of machines running the CP/M operating system.  The 5150 used an Intel 8088 CPU, a 16-bit processor with an 8-bit data bus, running at a blistering 4.77 MHz.  The most basic model had only 16 KB of RAM, and no other storage; more advanced models had one or two 5.25 inch floppy diskette drives (each diskette held 160 KB of data), and could use as much as 256 KB of RAM.  It was possible to use either a monochrome text or color graphics display.

The original IBM PC was never a great success in the consumer market, being somewhat pricey, but did get an unexpectedly positive reaction from businesses.  The timing of the introduction was good; spreadsheet programs had recently been introduced (VisiCalc, initially for the Apple II, and then Lotus 1-2-3 for the PC), and were proving to be a popular business tool.  And, of course, the new PC was from IBM, making it respectable to corporate customers.

In the longer term, the PC took off; in part because, ironically, it was not a typical IBM product.  The design had been produced by IBM’s Entry Systems Division in Boca Raton FL, and employed standard, off-the-shelf components.  Furthermore, the architecture of the system was unusually open; the original Technical Reference Manual included circuit diagrams, technical specs, and a complete assembly-language listing of the machine’s ROM BIOS [Basic Input-Output System].  (A site dedicated to the IBM 5150 has a downloadable copy [PDF] of the Technical Reference Manual, as well as some other documentation.)  Taken together, these characteristics meant that other manufacturers could build similar “clone” hardware, and reverse engineer the BIOS firmware, without infringing IBM’s copyrights.  Also, of course, the machine used Microsoft’s MS-DOS operating system (branded as PC-DOS by IBM), which Microsoft was more than happy to sell to the clone makers.

(I had been using IBM computers at work for more than a decade when the IBM PC was introduced, my first real personal computer was a PC clone made by Leading Edge.  I added an internal hard disk to the basic configuration, with a whopping 20 MB capacity.  While I had the cover off, I noticed that all of the memory slots seemed to be populated, even though the machine was sold as having only 128 KB of RAM.  With a little digging, I discovered that flipping a DIP switch on the motherboard gave me an instant 640 KB, which, as someone once said, ought to be enough for anyone.)

Although the original PC was not inexpensive (top-end models could run ~$6,000), the rapid growth of the clone market soon drove the price of hardware down; the open architecture of the system meant that all kinds of add-on products, from floppy diskettes to software, could be successfully sold as “IBM compatible”.  Apple, in contrast, made its own hardware and software, generally elegantly designed, but was unable to match the breadth and vibrancy of the PC market.   Microsoft, of course, benefited enormously from this expansion of the market for MS-DOS, and the opportunity it gave them to supplant IBM as a system software provider.  Ironically, as I discussed in an earlier post on the 20th anniversary of Microsoft Windows, it was the widespread availability of cheap PC  hardware  that made open-source projects like Linux and Mozilla Firefox possible.

Wired‘s “Gadget Lab” blog has an interesting photo essay on the evolution of the PC, starting with an image of one of the early IBM advertisements.

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