Full Introduction to DIMM (Dual In-Line Memory Module) [MiniTool Wiki]

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Introduction to DIMM

What is DIMM? It is short for dual in-line memory module. As a type of computer memory, it uses a 64-bit bus to the memory, which allows DIMMs to transfer data more quickly. A DIMM is a small circuit board that contains one or several random access memory (RAM) chips. It connects to the computer motherboard via pins.

DIMMs store each data bit in a separate memory cell. DIMMs adopt a 64-bit data path because the processors used in personal computers possess a 64-bit data width. DIMMs are commonly used in desktops, laptops, printers, and other devices.

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With the development of faster dynamic random access memory (DRAM), DIMM circuit boards have also evolved. Modern DIMMs based on double data rate fourth-generation (DDR4) SDRAM chips use 288-pin connectors to connect to computer motherboards, which improves data throughput.

With the increase of the clock speed of the RAM chip, the amount of data processed by the 64-bit path is also increasing.

Another development of DIMMs is the use of cooling fins or structures directly connected to the DIMM. In a typical 8 GB or 16 GB DIMM, an increase in chip density and an increase in clock speed lead to an increase in heat generation. Because DIMMs based on DDR4 RAM chips can be produced in capacities up to 64 GB, this situation is made worse.

The cooling structure on the DIMM helps to dissipate heat into the computer case and away from the motherboard and CPU.

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Types of DIMM

The most common standard DIMMs possess a typical length of 5.5 inches and a height of 1.18 inches, and they are listed below:

Unbuffered DIMMs (UDIMMs)

They are mainly used on desktop PCs and laptops. They run quicker and cost less, UDIMMs are not as stable as registered memory. Commands are sent directly from the memory controller residing in the CPU to the memory module.

Fully-buffered DIMMs (FB-DIMMs)

They are often used as main memory in systems that need large capacities, such as servers and workstations. FB-DIMM uses advanced memory buffer (AMB) chips to improve reliability, maintain signal integrity and boost error detection methods to reduce soft errors. The AMB bus is divided into a 14-bit read bus and a 10-bit write bus. With a dedicated read/write bus means that reads and writes can occur simultaneously, which improves performance.

Registered DIMMs (RDIMMs)

Registered DIMM is also called buffered memory, and RDIMMs are commonly used in servers and other applications that require robustness and stability. RDIMMs have on-board memory registers located between the memory and the memory controller.

The memory controller buffers command, addressing and clock cycling, and directs instructions to dedicated memory registers instead of directly accessing DRAM. Therefore, the instruction may take about one CPU cycle longer. Nevertheless, the buffering reduces the burden on the CPU's memory controller.

Load-reduced DIMMs (LR-DIMMs)

LR-DIMM uses isolation memory buffer (iMB) technology to buffer data and address lanes, thereby reducing the load on the memory controller. iMB chips also buffer data signals, while registers on RDIMMs only buffer commands, addressing, and clock cycling.

The iMB chip isolates all electrical loads from the memory controller, including the data signals of the DRAM chip on the DIMM. Thus, the memory controller can only see the iMB, not the DRAM chip. The memory buffer then handles all read and write operations to the DRAM chip, increasing capacity and speed.


Although standard DIMMs are in the form of rectangular sticks that are approximately 5.5 inches long, the small size dual in-line memory module (SO-DIMM) is only 2.74 inches in size, which is about half that. The most common height for both types of DIMMs is 1.2 inches, but both are made in a very low profile (VLP) and are only 0.8 inches high.

SO-DIMMs are mainly used in portable computing devices such as laptops and tablets. The difference from standard DIMMs is that DDR4 SO-DIMMs have 260 pins and DRR4 DIMMs have 288 pins. PCs and servers use standard DIMMs. VLP DIMMs were developed to meet the space requirements of blade servers.


There are some differences between DIMM vs SIMM, which are shown below:

  • DIMM is a double-sided SIMM. SIMMs can be installed in in-line pairs, but DIMMs are independent of the sides. Since the DIMM has separate contacts on each side of the board, it offers twice the amount of data as a single SIMM.
  • SIMM can have a maximum of 32-bit channels for data transmission while DIMMs support 64-bit channels.
  • SIMM consumes 5 volts of power while DIMM consumes 3.3 volts.
  • The SIMM module can store up to 64 bits. In contrast, DIMMs provide up to 1 GB.
  • SIMM is an outdated technology. The main reason for using DIMMs is that they outperform SIMM.

Bottom Line

To sum up, this post gives you detailed instructions for DIMM (dual in-line memory module). After reading this post, you can know that there are 5 types of DIMM and you can also know the differences between DIMM and SIMM.

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