What is DIMM(Dual Inline Memory Module)?

Before understanding about DIMM, it is good to have information regarding RAMs and its accessories and how it operates. 

A RAM is a chip made up of several electronic elements that store the temporary working data of your system which can be read and written. RAM requires electric supply for functioning, hence when the system is turned off, all data from RAM vanishes. It is mounted on the motherboard. 

The RAM chips are not individually mounted on the motherboard because of less capacity, hence in earlier times, several chips used to be soldered together and converted into “modules”(integrated circuit boards) and these modules were mounted over motherboard using “pins”(also known as connectors). 

Types of modules

There are two types of modules in a RAM: 

• Single In-line Memory Module(SIMM)
• Dual In-line Memory Module(DIMM)

In the case of SIMM, the connectors are only present on the single side of the module and are shorted together. SIMMs are always used in matched-pairs. The maximum data storage offered by SIMM is 32-bit/cycle and voltage consumption is 5 volts. 

As technology evolved, SIMM became obsolete and was replaced by DIMM. DIMM has the row of connectors on both the sides(front and back) of the module and connectors are independent. This resulted in twice the capacity of DIMM with the same quantity of RAM hence supporting the 64-bit processors. While two SIMM sticks would be used in parallel for 64-bit data width (which is a disadvantage!). The voltage consumption of DIMM is 3.3 volts which are comparatively lower. It is not backward compatible i.e it cannot be used on motherboards having SIMM slots. It is easier to replace damaged or corrupted RAM piece on DIMM. 

This proves that DIMM clearly outperforms SIMM in speed, latency, and power consumption. DIMM is generally available in 168, 184, 214 or 244 pins. 

Classification of DIMM

DIMM can be classified on the basis of buffer size and type of RAM: 

• DIMM classification based on buffer size:
  • Unbuffered DIMM (UDIMM): The system directly reads/writes from/to memory chip without validation hence increasing the electrical load on the motherboard but are very faster.
  • Registered DIMM (RDIMM): uses register that buffers signals, hence increasing clock cycle but are more reliable.
• DIMM classification based on the type of RAM:
  • SDRAM (synchronous dynamic RAM) DIMM: It was the first dynamic RAM to sync with the system clock. The refresh rate was much lower due to re-accessing data after the rising half cycle.
  • SDR(single data rate) DIMM: single data rate means the packet of data is only accessed once per clock cycle. Serial data can be read via the serial data pins on the DIMM which enables the motherboard to autoconfigure to the exact type of DIMM installed.
  • DDR(double data rate) DIMM: Data packet is accessed twice each clock cycle. DDR DIMMs also use two notches on each side to enable compatibility with both low- and high-profile latched sockets.
  • DDR2 DIMM: The key difference between DDR and DDR2 is that in DDR2 the bus is clocked at twice the speed of the memory cells, so data can be transferred four times faster per memory cell cycle.

How to select proper DIMM?

DIMM sizes vary from micro ATX to standard motherboards so no. of pins is an important factor. While purchasing a RAM stick, ratings are like 16 GB RAM can be 1X16GB(1 DIMM and 16 GB RAM each), 2X8GB(2 DIMM and 8 GB RAM each) or 4X4GB(4 DIMM and 4 GB RAM each). Operating frequency and maximum overclocking frequency should also be taken into consideration.