DRAM

A.

Out of the given options, the memory technology with the highest cost to implement is "Registered" memory.

Registered memory, also known as buffered memory, is a type of memory module that includes a buffer between the memory controller and the DRAM chips. The buffer reduces the electrical load on the memory controller by isolating the electrical load of each memory module. This enables the use of more memory modules than would otherwise be possible without the use of registered memory.

Registered memory is primarily used in servers, where large amounts of memory are required to support multiple users and applications. However, registered memory is generally more expensive than unbuffered memory due to the additional buffering components required in each module. Registered memory is also slower than unbuffered memory due to the added latency introduced by the buffer.

In contrast, ECC (Error-Correcting Code) memory adds an additional layer of error detection and correction to memory modules, which can improve system stability and reliability. While ECC memory is more expensive than non-ECC memory, it is not as expensive as registered memory.

RAID (Redundant Array of Independent Disks) is not a memory technology but rather a data storage technology that uses multiple hard drives to improve data availability and performance.

Pairing is also not a memory technology, but it could refer to the practice of pairing memory modules to ensure they are compatible with each other, which can improve system stability and performance. However, this practice does not necessarily add additional cost to the memory implementation process.

Therefore, the correct answer to the question is D. Registered.