"The 5155 was IBM's response to the Compaq Portable computer, which was released one year prior, costs $700 less, but has the same CPU and runs just as fast. The Compaq was advertised as being 100% IBM compatible, and even weighs slightly less.

This wasn't IBM's first portable computer, that would be the IBM 5100, released in 1975 - It was revolutionary, and extremely expensive"

I believe Jim's is the Compaq referred to.