Having cut my teeth on early Archimedes machines, I have a deep fondness for arm2's 16 instructions and the (lost during a house move, I suspect) assembly book I had that gave me enough of a description of the internals of the chip that I could desk check my assembly in my head with reasonable confidence that I was mentally emulating what the chip was actually doing rather than just what outputs I'd get for a given set of inputs.

Having to remember where I'd put the relevant chunk of assembler any time I needed a division routine was, admittedly, less fun, but the memories remain fond nevertheless :)