DOS for brains
You only think of one thing at one time, and can't remember anything else you were meant to be thinking about. You think only in words and never any pictures.

Unix for brains
Wow - you can think of lots of things all at once until your brain runs out of sockets. However, you can only talk with people who have brains made by the same vendor. Unfortunately you also never make any sense and have to read manuals to learn how to think. Predominantly a random thinker.

CP/M for brains
A very slow and old fashioned thinker. Any thing you remember has to be less than 3 letters long.

MVS/CICS for brains
You have a very big and expensive brain. You can think about many things at the same time but never know what other parts of your brain are thinking unless you have set up SNA connections between sections of your brains. You also need an army of system programmers to define what thoughts you may and may not have.

OS/2 for brains
You can think about lots of things at once but need the equivalent of eighteen sets of encyclopaedias in memory to produce any rational thought. No-one supports your way of thinking and many laugh at you whenever you speak.

Mac for brains
Simple thoughts for simple people. Thinking that looks good, feels good but is expensive.

Pick for brains
"I know no-thing. No-thing, Mr Fawlty".

AmigaOS for brains
You can think of lots of things at once, even with a very small memory. The trouble is that, sometimes, one thought starts to think about the things another thought was using. This leads to a compelling need to wrap a teatowel around your head and sit, crosslegged, on the floor.

Linux for Brains
You can think of any number of things and not run out of sockets. Unfortunately, there is no support for your particular limbs, ears, mouth or ... thingy ... available yet so you are reluctant to change over at this stage.