See the Apple Macintosh page for an extensive article.

It is now known that the Macintosh used in this presentation was not the original Macintosh, but a prototype of what would later become the Macintosh 512. This is because many applications did not work with the limited memory of 128 KB.

The first Macintosh used conventional cooling because Steve Jobs didn't want a fan in the machine. The machine suffered from overheating in the beginning. Limited memory was also a problem. The Macintosh 512 and Macintosh 128K came on the market relatively shortly after their introduction. It was better built internally and less prone to malfunctions. The 128 is actually a 512 with less memory on the mainboard and has long been sold as a budget model.