The Thumb-2 Instruction Set

The "Cortex" (ARMv6/v7) family introduced Thumb-2
It extended the thumb instruction set to be complete
Thumb now accesses all registers (not only 8 of them)
It includes coprocessor instructions
New ITE instruction (if then else)
It is a separate instruction decoder, not a decompressor any more

The design also changes how interrupt vectors work
There used to be 8 _instructions_ at address 00..1f
Vectors are now pointers rather than instructions (and many of them)
Moreover, "VIC" is offered as part of the core

So it is now possible to make thumb-only devices
But the core accesses RAM by itself, which I personally dislike

The Cortex-M family is a microcontroller flavour, thumb-2 only.
We have Cortex-M0, Cortex-M0+, Cortex-M3, Cortex-M4
They are all similar and all different. We'll learn to diffentiate