I bought a TRS-80 as a 14-year old in 1979. Commodore Pet, Apple II, and TRS-80 were the only real options. The Altair was an entirely different beast. Take a look at the Altair advertisement in the wikipedia entry and you'll get the idea: https://en.wikipedia.org/wiki/Altair_8800

The Altair didn’t come with a keyboard or screen. Just a front panel with lights and switches (like a PDP-11, to be fair). So, the fact that it wasn’t an integrated system in one box all from the same manufacturer distinguishes it as a Mini/Micro Computer rather than a Personal Computer.

The PET was the first personable computer.

I mean it's gotta at least have a keyboard…