The unit was a 600X featuring a 500-MHz Pentium III processor, 12GB hard drive and 13.3-inch display.
The ThinkPad 600, which IBM introduced in April 1998, is its most popular model, with 2 million units currently in use. The 1.4-inch-thick portable weighs about five pounds.
By contrast, the first ThinkPad, a 700C, came with a 25-MHz 486 processor, 4MB of memory expandable to 12MB, and a 10.4-inch display when it shipped in 1992.
The notebook line's consistent popularity has been remarkable in an industry noted for its constant and rapid change. Thinkpads, popular among business users willing to pay a little extra, have struck the right balance of features, battery life and weight.
Industrial designer Richard Sapper crafted the basic design of ThinkPad's elegant black case, accented by touches of blue, green and red. Sapper's approach was to create a portable that never went out of style. Beveled edges also give the illusion the notebooks are smaller and thinner than they actually are.
ThinkPad's most famous design innovation may have been the "butterfly" keyboard, which unfolded from within the notebook to full desktop size. IBM introduced the keyboard in March 1995 with the ThinkPad 701C, which is on permanent display at the Museum of Modern Art.
The ThinkPad 560 followed the trend of unusual design. At 1.2 inches thick and weighing 4.1 pounds, the 560, which IBM introduced in May 1996, started an industry shift to thinner and lighter portables.
Other ThinkPad firsts include color displays, 14-inch displays, full-sized keyboard, DVD drives and removable hard drives. The portables have also flown on every space shuttle mission since Dec. 2, 1993, including a recent earth-mapping mission.
IBM hopes to extend its emphasis on design and functionality in May, when it unveils the first ThinkPads with the Portofino port, a connection for snapping in wireless modems, cameras and other devices.
Meanwhile, the company plans to extend the 560's portability to new areas. The company is developing a wearable PC based on the model.