It was August 1981 when IBM released the Personal Computer Model 5150. Costing $1,265, it didn't have a monitor, parallel ports or even a hard disk. To the casual observer, it was more of a box than a computer.

But it sold like crazy, even after the wild success of other revolutionary computers, like the Apple II in 1977 and the Atari 800 in 1979.

The 5150's open architecture and use of third-party hardware and software certainly had something to do with its success, but we can't help but feel like the over-the-top marketing campaign with a Charlie Chaplin lookalike played a role as well.

(See one of the original commercials at the bottom of this post.)

This computer was the first one to be a truly open system -- it was customizable, users could install whatever they wanted and easily write their own software. Internally, the machine boasted a 4.77 MHz Intel 8088 processor and a 256K RAM.

Of course these specs sound like a joke compared to modern hardware, but they were groundbreaking for their time. Impressive work, considering it was designed by a team of just 12 people working out of Florida.

The 5150 was so important that it inspired a lot of reverse engineering, yielding an entire market of PC-compatible systems. Newer PCs quickly put IBM in the shadow of other computer companies. IBM eventually sold its PC division to Lenovo in 2005.