A fully buffered DIMM (Dual In-Line Memory Module) is a Random Access Memory (RAM) chip that contains an advanced memory buffer on the chipset. The advanced memory buffer acts as a middleman between the actual memory modules and the memory controller. This enables the available memory on the chip to be increased without increasing the number of pins on the module. The disadvantages of DIMMs include the introduction of latency and an increase in power consumption for the chipset.
On a fully buffered DIMM, the advanced memory buffer sits right between the memory module(s) and the memory controller. All data moving to and from the memory modules must first pass through the advanced memory buffer unit. Unlike unbuffered DIMMs, where the memory controller directly interfaces with the memory module, information on the fully buffered DIMM must be "interpreted" by the advanced memory buffer.
Using a fully buffered DIMM allows for two primary advantages. The first is that the signal can be restored by the memory buffer unit, compensating for deterioration as it travels through the computer bus architecture. The second is that the advanced memory buffer can perform preemptive error-checking on the data flowing to and from the RAM chip. It acts like a type of miniature brain that can tell whether the data passing through has been corrupted at any point during the process.
There are also disadvantages to using a fully buffered DIMM, though. The first of these is that the advanced memory buffer requires additional power consumption for the RAM chip. This means that the RAM socket must be set at a higher voltage level. Increased power produces extra heat, which can shorten the life of RAM chips — and other components within the system — within poorly ventilated conditions. To minimize this risk, additional cooling should be used; this can include additional exhaust fans for the case or another type of cooling solution to improve airflow across the RAM chips.
The last disadvantage of DIMMs is that relying on the advanced memory buffer introduces the concept of latency to RAM operations. Without a buffer, RAM operations essentially occur in real-time, limited only by the speed of the processor, the front side bus between the processor and memory, and the speed of the RAM chips themselves. However, once data is channeled through the advanced memory buffer, a delay occurs between receiving and processing the information. The only possible compensation for this is using faster memory modules, to overcome the inherent latency delay.