Oh gosh...dare I open this can of worms.

RAM can have buffers.
RAM can be unbuffered
RAM can have registers
Registers are not buffers.

Therefore:

You can have unbuffered ECC Registered memory.
You can have buffered Registered Memory.
You can have unbuffered ECC memory.
You can have unbuffered memory.
You can have buffered ECC Registered memory.



I believe non-parity = "non-registered"
I believe parity = "registered"

ECC Reg and unbuffered - non-parity are the two most common for our particular world.