is all of this possible?

[Simon F]

Is fixed ratio lossless compression actually impossible as a mathematical exercise so to speak, or just imposible on the hardware we have ?

Mathematically impossible based on a "pigeon hole principle" argument. It is impossible to take the set of possible N bit values and squash them into N-k bits.

 

[Davros]

I remember making a program that could do lossless compression with a fixed ratio of between 1 and a 100ish, more or less, give or take a dozen or two

 

[Simon F]

I remember making a program that could do lossless compression with a fixed ratio of between 1 and a 100ish, more or less, give or take a dozen or two

On what data? Sure there will exist a subset of all data sets which will be compressed by a given lossless compression algorithm but that algorithm must expand the remainder [pedantic edit] ...except for a set which may stay the same size[/pedantic edit].