Registered module
The term register module or registered module (also called R- DIMM , RDIMM , registered memory or registered RAM ) describes a type of memory module that is often used in the main memory of servers and workstations . The aim of the technology is to use additional registers to reduce the electrical, capacitive load on the memory controller and thus to increase the possible number of connectable memory chips as well as the data integrity . The term is often incorrectly used synonymously with the predecessor technology Buffered Module ("buffered module"), since both pursue similar goals. Another recent development of buffered modules is LR-DIMM (Load-Reduced DIMM), in which the registers are replaced by memory buffers.
In contrast, the more common variants for desktop PCs are the " unbuffered " or " unregistered " modules. These two different types of RAM in two-tier design are abbreviated to RDIMM (= registered) or UDIMM (unbuffered).
Registered memories are offered for SDR, DDR, DDR2, DDR3 and now for DDR4 SDRAM.
functionality
Since the introduction of SDRAM , also applicable to DDR-SDRAM , there are no more buffers on the modules, but registers, which is why we speak of Registered RAM. In the time before that, up to the era of EDO-RAM , a corresponding technology with buffers, called buffered modules , was used.
Registered memory modules have additional (usually two) Register chips through which the signals from the address lines are made to the electrical load on the main board - chipset to reduce. In addition, there is usually a PLL module that is used to prepare the clock signal and relieve the clock signal driver of the mainboard. With unregistered modules, not only are the data lines of all modules connected in parallel, but also the address line inputs of all memory chips. In contrast, Registered modules relieve the address driver lines so that the chipset works more stably. As a result, these modules are often organized differently. Instead of double-sided modules (two banks), single-sided modules (one bank) are often used to relieve the data signal line drivers because fewer chips are connected in parallel. Registered modules are almost exclusively available as an ECC version, which often means that both terms are mentioned in the same breath, although they are two separate technical properties.
disadvantage
However, the technology has some disadvantages. The technical effort is higher, usually the additional register chip is clearly visible in the center of the DIMM . In addition to the higher prices of the modules and the absolutely necessary support from the motherboard, including the BIOS , latency and thus data throughput play an important role. With Registered modules, the input signals only appear at the outputs exactly one clock cycle later than is the case with normal modules. In addition, Registered - DIMMs have a slightly different pin assignment of the 240 pins than normal modules, which is automatically recognized by suitable memory controllers. It should be noted that Registered modules cannot be combined with Unregistered modules and that manufacturer references to support (only) of "unbuffered" DDR-3 usually imply the non-support of "registered" DDR-3. Registers cannot be deactivated either, as is the case with ECC, for example. In addition, the power consumption of the Registered modules is usually slightly higher than that of conventional DIMMs.