No

Registered memory buffers the address and control signals going on to the module, and improves the stability of systems with large amounts of memory.
Some older computers need registered memory if they are upgraded to 512mb and higher.
Check your systems manual for compatibility.

Registered modules have additional components (registers) placed between the incoming address and the memorycomponents. The registers re-drive the signals through the memory chips. These modules are usually associated with ECC and typically used in servers due to their added reliability.

Yes

ECC is an acronym for Error Correction Code. ECC is used in mission critical applications so that the system will not crash if a memory cell loses data. The extra memory, on the memory module, is used by the computer to check the integrity of the data.
ECC memory is used in servers and workstations and is not commonly used in notebooks or desktop computers.
A system must be designed to use ECC. Check your systems manual for compatibility.

Yes

Non ECC or nonParity memory with have either 2, 4, 8, 16, or 32 chips on the memory module.
ECC or Parity memory will have either 3, 6, 9, 12, 18, or 36 chips on the memory module.

Non ECC or nonParity memory with have either 2, 4, 8, 16, or 32 chips on the memory module.
ECC or Parity memory will have either 3, 6, 9, 12, 18, or 36 chips on the memory module.

ECC memory is used in servers and workstations where data and system reliability is crucial. The ECC protects the system from a memory bit error. The downside is it is more expensive and decrease memory performance.
A system has to be designed to use ECC, not all systems can use ECC.