Comprehensive Guide to Memory Module Standards and Speed Ratings: Mainstream Types and Key Points Explained

Memory capacity is the most important factor when choosing memory, but there are other crucial points such as module standards, memory standards, and data transfer speed standards. If these are mistaken when building a custom PC, it may become impossible to assemble the system.

Also, memory standards like DDR4 and DDR5 change every 3 to 7 years, so this article will also explain the current mainstream standards.

Even though the term “memory standard” is used, there are various types, and these points are important for performance and when building a custom PC. It is important to understand them well.

When building a custom PC, it is essential to choose memory that matches the intended use.

Basically, for custom PCs, choosing the DIMM module standard for desktops and either DDR5 or DDR4 memory standard is sufficient.

This article also explains how to choose memory from the perspectives of basic knowledge, performance, and compatibility.

≫ Related article: How to Choose Memory for Custom PCs [Performance / Features / Compatibility]

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About Memory Standards

There are three main types of memory standards:

• Module standard
• Memory standard
• Memory speed standard

If the module standard or memory standard is mistaken, the memory cannot be physically inserted into the motherboard’s memory slot, so caution is required.

Also, memory standards change every 3 to 7 years, and usually two generations of memory standards are available on the market. This article will also explain which standard is currently mainstream and which one to choose now.

Module Standard

The memory module standard is a guideline that standardizes the physical shape and pin layout of memory to ensure compatibility with various products and systems.

If purchasing a pre-built PC from a manufacturer, users do not need to worry about this, but when building a custom PC, the module standard must match the motherboard.

If not matched, the memory cannot be physically inserted into the slot, so be careful.

There are various module standards, but for custom PCs, the two minimum standards to know are:

• “DIMM” for desktop PCs
• “SO-DIMM” for laptop PCs

As can be seen, the sizes are very different, and laptop memory is smaller to fit the compact chassis.

Since custom PCs are mainly desktops, DIMM is basically the only choice.

However, some motherboards for small PCs or barebone mini PC kits may use SO-DIMM, so be aware of this possibility.

Memory Standard

The memory standard defines the technical characteristics and performance of memory, such as compatibility, speed, size, and power consumption.

The memory standards currently in use are:

• DDR5 SDRAM
• DDR4 SDRAM

SDRAM is often omitted, and people simply say “DDR5” or “DDR4”.

DDR4 appeared around 2014, and DDR5 around 2021. As of 2024, both standards are in use, with a gradual shift to DDR5.

With each new generation, such as DDR2, DDR3, and DDR4, data transfer speeds have increased and power consumption has decreased.

Top: DDR3, Bottom: DDR4

If the module standard is the same, such as DIMM, they may look similar at first glance, but the position of the notch is different.

The image shows DDR3 and DDR4 memory, but DDR5 is also different in the same way.

Therefore, if the motherboard’s memory standard (DDR5, DDR4) is different, the notch position will not match, and the memory cannot be physically inserted, just like with the module standard.

When choosing memory, pay attention to the memory slot standard on the motherboard.

Memory Speed Standard

The memory speed standard refers to the data transfer speed of memory, indicating how fast data can be read and written.

For example, it may be written as “PC5-38400 (DDR5-4800)”.

“PC5” in PC5-38400 indicates DDR5, and “38400” means the theoretical maximum data transfer speed is 38,400MB/s (about 38GB/s).

The number in parentheses, “4800”, means the data transfer speed is 4800MT/s (mega transfers per second).

If the memory data bus width is 8 bytes, 4800 × 8 = 38,400, so MT/s can be converted to the more familiar MB/s.

In some cases, such as 3D games, memory speed can affect FPS by about 10%, but even so, memory speed is generally not considered the most important factor.

Increasing memory speed often raises the price significantly, but rather than focusing on this, it is often better to use the extra budget to upgrade the CPU or GPU, which will improve the overall processing speed of the PC.

Therefore, it is not necessary to be overly concerned with high memory speed.

There are various memory speeds for each memory standard, so a table will be provided later for those who want to know specific numbers.

Current Mainstream Memory Standards

The current mainstream memory standards are DDR5 and DDR4.

Also, although not a standard, dual channel configuration, which uses two sticks as a pair, is common.

DDR5 memory was introduced in 2021 and about three years have passed, but it is still much more expensive than DDR4, making it harder to purchase.

For example, comparing 16GB memory, DDR5 costs about 7,000–15,000 yen, while DDR4 costs about 4,000–7,000 yen.

There is about a twofold price difference.

Although this is a transition period to DDR5, the high price means that many people still build custom PCs with DDR4.

Even pre-built PCs still often use DDR4 memory.

Some high-end PCs costing 400,000–500,000 yen may have DDR5, but it is not yet common.

However, prices are expected to drop, and eventually DDR5 will become the standard.

Some may worry that if a custom PC is built with DDR4 now, DDR4 memory may become more expensive or harder to find in 3–4 years when upgrading. However, research shows that even older DDR3 memory has not become more expensive or difficult to obtain, so there is no need to worry.

Memory Module Standards

There are several memory module standards.

The mainstream module standards introduced are “DIMM” for desktops and “SO-DIMM” for laptops, but there are a few other types as well.

For custom PCs, knowing just DIMM and SO-DIMM is sufficient.

DIMM

DIMM (Dual Inline Memory Module) is the standard memory module for general desktop PCs that does not use buffers or registers.

It communicates directly with the memory controller, resulting in relatively low latency, and its simple structure tends to keep costs low.

DIMM is almost always used when building custom PCs.

SO-DIMM

SO-DIMM (Small Outline Dual Inline Memory Module) is a memory module standard used in laptops and small PCs.

Compared to DIMM for desktops, it is smaller and suitable for devices that require space-saving.

Custom PCs are generally desktops, so SO-DIMM is rarely used, but some motherboards for small PCs or barebone mini PC kits may use SO-DIMM.

Therefore, those considering mini PCs should check that the memory and motherboard module standards match.

MicroDIMM

MicroDIMM is a memory module standard that is even smaller than SO-DIMM and is especially suitable for compact laptops.

This standard is designed to make effective use of limited space and enables high-performance memory in a small form factor.

Compared to regular DIMM, it has fewer pins and is smaller, contributing to the development of lightweight and portable mobile devices.

By adopting MicroDIMM, manufacturers can offer thinner and lighter laptops, improving portability for users.

However, due to its small size, expandability is limited, so this should be considered when planning upgrades.

RDIMM

RDIMM (Registered DIMM) is a memory module that uses registers to stabilize data signals and is mainly used in servers, workstations, and environments that require high stability and large memory capacity.

The register stabilizes the signals between the memory controller and memory chips, improving signal integrity.

This increases memory reliability and stability, allowing more memory modules to be stably installed in the system.

The size is the same as DIMM, but the register (buffer) chip is mounted, so visually there are more black chips.

LRDIMM

LRDIMM (Load-Reduced DIMM) is designed to reduce the load on the memory bus and is used in server systems that require large memory capacity.

By reducing the load, it prevents performance degradation of memory and the entire server, allowing the memory controller to efficiently manage more memory.

Memory Standards and Memory Speeds

There are several memory standards.

This article briefly touched on the mainstream “DDR5” and “DDR4”, but will now explain all memory standards in more detail.

DDR3 and earlier are not used for new builds, so they can generally be ignored.

The only exception is if memory for an existing PC needs to be replaced, upgraded, or repaired.

DDR5 SDRAM

DDR5 SDRAM is the latest memory standard, featuring high data transfer speeds and large capacity.

The standard was announced in 2020 and introduced to the market around 2021.

It achieves more efficient power management and improved signal integrity, making it suitable for high-performance gaming PCs, servers, and data centers.

High bandwidth and low latency are essential for next-generation applications such as advanced 3D games and AI, enabling smooth processing of complex data.

The main changes from DDR4 SDRAM are:

• Memory clock: 2,000–4,200MHz or higher
• Voltage: reduced to 1.1V
• Significant improvement in data transfer speed and bandwidth.
• Improved channel architecture for faster data processing.

Memory Speed Standard Specifications

DDR4 SDRAM

DDR4 SDRAM is a high-speed and efficient memory standard widely used to improve computer performance.

It was introduced to the market around 2014.

Compared to the previous generation DDR3, data transfer speed is greatly improved, and it operates at a lower voltage, reducing power consumption.

This enables efficient memory operation in desktops, laptops, and servers, allowing smoother multitasking and large data processing.

Additionally, error correction features are enhanced, increasing data reliability, which is valuable for enterprise servers and data centers.

The main changes from DDR3 SDRAM are:

• Main clock: 400–2,800MHz or higher
• Voltage: reduced to 1.2V
• Increased capacity and further improved power efficiency.
• Enhanced error correction features.
• Double transfer speed with bank groups

Memory Speed Standard Specifications

DDR3 SDRAM

DDR3 SDRAM is a memory standard with faster data transfer and lower power consumption.

It was introduced to the market around 2007 as the successor to DDR2 SDRAM.

It also reduced operating voltage to 1.5V, lowering power consumption and making it suitable for mobile devices such as laptops.

With DDR4 and DDR5 now mainstream, DDR3 is rarely used for new builds and is mainly used for repairs, upgrades, or replacements in existing systems.

The main changes from DDR2 SDRAM are:

• Main clock: 400–1,333MHz or higher
• Voltage: reduced to 1.5V
• Higher density and improved power efficiency.

Memory Speed Standard Specifications

DDR2 SDRAM

DDR2 SDRAM is a memory standard that achieves faster data transfer and lower power consumption. It was introduced to the market around 2003 as the successor to DDR.

Compared to DDR, it features higher memory clock and doubled transfer speed.

The main changes from DDR SDRAM are:

• Main clock: 200–666MHz or higher
• Voltage: reduced to 1.8V
• Faster speed due to increased bus width and more internal banks.

Memory Speed Standard Specifications

DDR SDRAM

DDR SDRAM is a memory standard supporting double data rate (DDR), introduced to the market around 2000.

Double data rate means data is transferred on both the rising and falling edges of the clock cycle, greatly increasing data transfer speed compared to conventional SDRAM.

Previously, data could only be transferred in one direction at a time, but with DDR, data can be transferred in both directions at once, doubling the speed.

The main changes from SDRAM are:

• Main clock: 200–550MHz
• Voltage: 2.5V
• Data transfer speed is about twice that of SDRAM.

Memory Speed Standard Specifications

SDRAM

SDRAM stands for Synchronous Dynamic Random Access Memory, a memory standard that operates in sync with the system clock when reading and writing data.

It appeared in the 1990s and has since been widely adopted as the main memory standard for PCs.

Unlike conventional asynchronous DRAM, SDRAM operates in sync with the CPU’s timing, enabling efficient memory operations.

This improves data processing speed between the CPU and memory, allowing efficient data access.

In summary, SDRAM:

• The first synchronous memory technology.
• Main clock: 66–133MHz

Summary: For Custom PCs, Choose DIMM Module Standard and DDR5 or DDR4

This article explained memory standards, and for those starting custom PC building, basically choosing the DIMM module standard for desktops and either DDR5 or DDR4 memory standard is sufficient.

Although DDR5 is a bit more expensive, it will become mainstream in the future, so it is fine to choose it, or choose DDR4 for cost savings.

Here is a summary of the key points again.

If the memory slot standard on the motherboard is mistaken, the memory cannot be physically inserted, so be careful when choosing parts.

A tool is also available to check compatibility, including memory standards and other compatibility check tools, so please make use of it.

This article also explained memory speed standards, but the top priority for memory is capacity, and speed is often not a major concern.

Increasing memory speed raises the price significantly, and it is often better to use the extra budget to upgrade the CPU or GPU, which will improve the overall processing speed of the PC.

When building a custom PC, it is important to choose memory that matches the intended use.

This article also explains how to choose memory from the perspectives of basic knowledge, performance, and compatibility.

≫ Related article: How to Choose Memory for Custom PCs [Performance / Features / Compatibility]

あわせて読みたい

PC Parts Estimation & Compatibility Check Tool

Automatically checks each component you need when selecting parts for a custom-built PC—perfect for beginners.