No matter how you're reading this, you're reading it on a device unfathomably more powerful than the 4.77 Mhz IBM 5150 PC. But 30 years ago, that machine was so powerful, it defined what PC meant for the entire world.
In 1981, the desktop computer was still mostly relegated to the business world. But it was thriving—a multitude of competing companies with competing formats pushed out bulky boxes with bulky monitors. You've never heard of most of them, because the IBM 5150 murdered them all very shortly after its release. It started at $1,565—highly affordable for the time—and offered a floppy disk option, a simple, text-based interface, available at your local Sears Roebuck or Computerland (this was a long time ago!).
The spread of the 5150, and the demise of competitors, established IBM as the de facto personal computer system of the world. Rivals made their own versions—clones—but they were all based on IBM's engineering, and "IBM compatibility" became the prime cachet of the time, as "iPod compatible" would many, many years later.
And now, IBM doesn't even build commercial computers. But the ascendancy of the PC—the very fact that the term became a generic—started with the 5150's dominion.