Before the Mac, there was the Lisa, Apple’s first computer with a graphical user interface. Lisa was released 40 years ago this week, and to celebrate the anniversary, the Computer History Museum, which calls Lisa “Apple’s biggest failure,” is offering a free download of Lisa’s software source code.

The download is only 7 MB compressed, 30 MB expanded. However, you must agree to the license agreement before you can receive the download and provide your name and email address. And then once you’ve downloaded it, you’ll need to figure out how to run it.

Looking at Lisa’s graphical interface, you’ll immediately understand where Macs come from. In fact, the Mac desktop still takes its cues from Lisa, with drop-down menus at the top and icons for files and apps. The Lisa software ran on the Motorola 68000 and even allowed for multitasking, but the 6800 had a hard time keeping up with the Lisa software and the computer was slow and expensive, and became a footnote after the Mac launched in 1984.

Named after the daughter of Steve Jobs, the Lisa computer debuted on January 19, 1983. It cost $9,995, several thousand dollars more than IBM’s command-line computers. Apple hoped that the GUI would be enough to overcome the high price and poor performance, but the computer did not sell.

The Macintosh debuted in 1984 at a more reasonable $2495, Apple also released new Lisa computers at the same time, but it was the Mac that caught on and the Lisa was eventually scrapped. Suffice it to say that without Lisa, there would be no Mac, and the history of the car is fascinating. To learn more about the history of Lisa, visit the Computer History Museum website.

The Computer History Museum, located in Mountain View, California (about 9 miles north of Apple Park in Cupertino), is hosting a 40th birthday event for Lisa. Speakers who were part of the Lisa development team are featured, such as Bill Atkinson, Bruce Daniels and John Coach. The event will also feature live demonstrations of the Lisa computer and an Apple-style scavenger hunt. The event will take place on January 31 at 5:30 pm PT and registration is required.