Which of the following statements is true regarding single- and double-sided memory?

Types of DIMM

The most common standard DIMMs, with a typical length of 5.5 inches and height of 1.18 inches, are:

• Unbuffered DIMMs (UDIMMs) -- Used mainly on desktop and laptop computers. Although they run faster and cost less, UDIMMs aren’t as stable as registered memory. Commands go directly from the memory controller residing in the CPU to the memory module.
• Fully-buffered DIMMs (FB-DIMMs) – Usually used as main memory in systems that require large capacities, such as servers and workstations. FB-DIMMs use advanced memory buffer (AMB) chips to boost reliability, maintain signal integrity and improve methods to detect errors to reduce soft errors. The AMB bus is split into a 14-bit read bus and a 10-bit write bus. Having a dedicated read/write bus means reads and writes can happen at the same, which results in increased performance.
• Registered DIMMs (RDIMMs) -- Also known as buffered memory, RDIMMs are often used in servers and other applications that require robustness and stability. RDIMMs feature onboard memory registers that are placed between the memory and the memory controller. The memory controller buffers command, addressing and clock cycling, and directs instructions to the dedicated memory registers rather than directly accessing the DRAM. Consequently, the instructions could take about one CPU cycle longer. However, the buffering reduces the strain on the CPU's memory controller.
• Load-reduced DIMMs (LR-DIMMs) – Use isolation memory buffer (iMB) technology that buffers the data and address lanes, reducing the load on the memory controller. The iMB chip also buffers data signals, unlike the register on RDIMMs, which only buffers command, addressing and clock cycling. The iMB chip isolates all electrical loading, including data signals of the DRAM chips on the DIMM from the memory controller. As a result, the memory controller only sees the iMB and not the DRAM chips. The memory buffer then handles all the reads and writes to the DRAM chips, enhancing capacity and speed.
• SO-DIMM -- While the standard DIMM is in the form of a rectangular stick approximately 5.5 inches in length, the small outline dual in-line memory module (SO-DIMM) is about half that size at 2.74 inches long. Both types of DIMMs are most commonly 1.2 inches tall, but both are made in a very low profile (VLP) format that is only 0.8 inches tall. SO-DIMM is mainly used for portable computing devices such as laptops and tablets. It differs from standard DIMM in that the DDR4 SO-DIMM has 260 pins versus 288 pins for the DRR4 DIMM. Standard DIMMs are used in PCs and servers. The VLP DIMM was developed to meet the space requirements of blade servers.

DIMM vs. SIMM

The main differences between DIMM and SIMM are:

• A DIMM is a double sided SIMM. SIMM can be installed in in-line pairs while DIMM is independent of the side. Because a DIMM has separate contacts on each side of the board, it provides twice as much data as a single SIMM.
• SIMM can have a maximum 32-bit channel for data transfer. In contrast, DIMM supports 64-bit channel.
• The amount of power consumed by SIMM is 5 volts and 3.3 volts for DIMM.
• SIMM modules can store at maximum 64 bits. On the contrary, DIMM offers up to 1 GB.
• SIMM is outdated technology. DIMM is used mainly because its performance is better than SIMM.

The future of DIMM

In 2018, the JEDEC standards organization published specifications for DDR5 and several manufacturers have said that they’ll release commercial DDR5 by the end of 2019. DDR5 will double the top data transfer rates of 25 GBs of DDR4 and use less power than DDR4.

However, DDR5 isn’t the only type of DIMM development coming. JEDEC is also working on new standards for non-volatile DIMM (NVDIMM) that would retain data during a power outage. NVDIMMs integrate non-volatile NAND flash memory with DRAM and dedicated backup power on a single memory subsystem.

Intel and Micron launched 3D XPoint in July 2015 as the first new memory architecture in decades. The chips finally shipped in both solid-state drives (SSDs) and DIMMs in May 2019, two years after they were supposed to be launched.

In 2015, some analysts forecast that Intel could get up to $2 billion in revenue in the first two years after these chips were introduced. However, now they say a more realistic figure is about $200,000 since memory prices have been collapsing.

Micron is expanding its production capacities produce next-generation memories for next-generation applications. The company is currently preparing 32 GB memory modules for client systems as well as 64 GB DIMMs for servers based on its 16 GB DDR4 memory chips.