My semi-educated guess is that mainframes are a much bigger chunk still.

(AS/400 is midrange. They are called something else now, I heard. Maybe I-series.)

A lot of those indispensable infrastructure systems we all depend on, such as insurance, income tax, etc., run on mainframes, as they have for decades now.

So don't diss big iron / Big Blue.

I, for one, hope they have many years left, though I guess they could do with improving their corporate culture and business practices some.