[ameasure]

If you're interested in comparing the various market shares, a simple bar chart is much easier to understand, just look at which one is taller.

With these rectangle/tree map things, I never know what to think: well this one is wider, but this other one is taller; you have to do multiplication just to compare 2 market shares.

[Terretta]

This diagram is a collection of bar charts. One bar chart running horizontally, showing OS, the other bar chart(s) vertical, showing manufacturers within an OS. It could be disassembled, certainly, but then doesn't as readily show the sets and subsets of who has how much relative share of the whole.