But still data is stored in 8 bits. 9th bit holds information whether "byte" contains slave address or frame data. so that when slave listens and if it receives byte with 9th bit set and the rest is it's own address, then it can start to interpret following bytes. Otherwise it can ignore following data.

Maybe that comment is not so relevant to thread, but one may be curious how it works.

The IBM 704 used 6 bit bytes (and 36 bit words).

A number of people have toyed with ternary (commonly the digits are -1, 0, and +1).

https://en.wikipedia.org/wiki/Setun https://ieeexplore.ieee.org/document/1498715