1. Server RAM Basics

In this blog post, we’ll explore the differences between server memory (server RAM) and traditional RAM used in desktop PCs and laptops. Although both types of RAM perform the same basic function of providing a volatile cache for quick access to data, there are some important differences.

The term ” server RAM ” can be misleading, as server hardware is designed for completely different applications than PC hardware, such as running continuously 24 hours a day. The modules used generally have a higher storage density and therefore a higher total capacity. A basic property of server RAM modules is that the memory has error correction.

Basically, any RAM can be used in a PC, as long as the motherboard and CPU support the specific features of the respective module. You can find out which RAM is compatible in your computer or server via our online store.

In short, server hardware is different in that it is typically designed for continuous operation and offers higher data integrity than PC components. Because of these specific characteristics, server components are usually more expensive than typical PC hardware. However, if you are looking to upgrade a server or need a more robust computer system with more capacity and error correction, you should consider using server components.

Different types of ECC server memory:

The following variants of RAM memory with error correction are currently available:

Unbuffered ECC (DIMM) – Standard PCs and workstations, not servers
Registered ECC (RDIMM) – Server and high-end systems
Load-Reduced ECC (LRDIMM) – energy-efficient servers and high-end systems

2. ECC RAM (Unbuffered ECC - DIMM)

The unbuffered ECC DIMM module (DIMM = Dual Inline Memory Module) is the simplest form of RAM memory with ECC functionality. A distinction is made between UDIMM ECC modules for desktop systems, workstations and small servers and SO-DIMM ECC modules for mobile workstations and storage systems.

2.1 Error Correction (ECC): Importance & Benefits for Servers

Server RAM memory usually has ECC (Error-Correcting Code) functionality, which can detect and correct memory errors. This is crucial for servers, as they are in continuous operation and data loss can have catastrophic consequences for business-critical areas. Conventional RAM, on the other hand, usually does not have ECC support, and a memory error here leads to system crashes, blue screens, uncontrolled reboots and possibly data loss.

Data integrity is critical for servers. A single bit error in memory can lead to system crashes, data loss, and inconsistent data. This is where ECC memory comes in and prevents such failures.

2.2 Server RAM error correction: How it works

The ECC function in server memory prevents system crashes and is a technology that detects and corrects errors in the main memory. With the help of an additional data bit in the RAM memory, redundant data is generated in the memory chip. The ECC memory can correct a 1-bit error immediately. If 2 or more bit errors are detected, this does not lead to a system crash. Instead, the memory errors are logged and reported. Data loss is avoided and data integrity is thus guaranteed.

2.3 ECC memory offers several advantages for servers:

Greater data integrity: ECC memory can prevent data loss due to memory errors. This is especially important for companies that work with sensitive data, such as databases and financial systems.
Greater reliability: For demanding systems that operate around the clock and are subject to high levels of stress.
Improved system stability: ECC memory can detect bit errors, reducing or completely avoiding system crashes. This in turn leads to higher server availability and productivity.
Reduced maintenance costs: ECC memory can reduce the cost of maintaining and repairing servers by reducing the likelihood of hardware failures.

2.4 ECC vs. Non-ECC RAM for Servers

ECC server memory is generally a little more expensive than conventional non-ECC memory, but the advantages outweigh the disadvantages in most cases. ECC memory is indispensable, especially for servers and workstations that work with sensitive data or require high availability.

Conventional memory (non-ECC) is usually used when the system only runs for a few hours a day, the memory sizes are smaller, the RAM memory is usually only used to a fraction of its capacity and system crashes do not have far-reaching consequences for the existing data.

However, the use of ECC server RAM modules is only possible in devices such as workstations, servers and high-end devices that are designed for ECC operation and support this feature.

3. RDIMM – Buffered RAM (Registered DIMM)

In contrast to the unbuffered ECC modules, the RDIMM server RAMs are buffered RAM. The other properties of an ECC RAM memory are identical, however.

3.1 What does buffered RAM mean?

Buffered RAM is a type of memory module that has an additional buffer placed between the memory chips and the memory controller.

The main function of the buffer is to reduce the electrical load on the memory controller by stabilizing the signals and buffering (caching) the data before sending it to the memory controller. This allows more memory chips to be used on a module, thus increasing the overall capacity of the system without compromising stability.

Buffered RAM is typically used in servers and workstations where large storage capacity and reliability are extremely important. However, buffered RAM modules usually have higher latency compared to unbuffered RAM modules because the data has to pass through the additional buffer.

In summary, “buffered” in a RAM means that the RAM module has an additional buffer that is placed between the memory chips and the memory controller to increase stability and reduce the electrical load on the memory controller.

3.2 RDIMM memory: advantages and disadvantages

Advantages:

Higher memory capacities: The maximum memory capacity per memory module is up to 4x higher when using RDIMM modules compared to UDIMM or UDIMM-ECC modules.
Improved stability: Using RDIMM modules improves data integrity and reduces the likelihood of memory errors. This is especially important in high-utilization environments where high system availability is required.
Increased scalability: RDIMM server RAM allows more memory modules to be used in a system than UDIMM or UDIMM-ECC. This can increase the overall memory capacity of the system and improve performance in memory-intensive applications.
Improved error management: RDIMM RAM memory can better detect and report memory errors, making server troubleshooting and maintenance easier.

Disadvantages:

Higher cost: RDIMM memory is typically more expensive than UDIMM or UDIMM-ECC memory modules.
Increased complexity: RDIMM RAMs are only found in servers, workstations and high-end devices and require the use of processors that support this memory technology.
Higher latency: The operating speed of the memory is reduced by the buffer function of the RDIMM module.
Reduced compatibility: Many systems require an exact RAM specification of the RDIMM memory module. This is the only way to ensure that the memory modules function correctly in the system. Using or mixing different RDIMM variants is often not possible.

3.3 RDIMM variants

RDIMM – Standard RDIMM
RDIMM – DDP (Dual-Die-Package)
RDIMM – 3DS (3-Dimensional-Stacking)

3.3.1 RDIMM - Standard RDIMM

RDIMM memory modules are available with a capacity of 4, 8 and 16 GB in DDR3, as well as 4, 8, 16, 32 and 64 GB in DDR4, as well as 16, 32, 64 GB in DDR5.

The typical memory organizations for RDIMM modules (standard RDIMM modules) are 1Rx4, 2Rx4, 1Rx8 and 2Rx8, where the number before the R stands for the number of ranks (1 = single rank, 2 = dual rank) and the number after the x defines the width of the DRAM.

3.3.2 RDIMM – DDP (Dual-Die-Package)

To enable larger storage capacities, other storage technologies are needed.

RDIMM-DDP memory is a type of RDIMM that uses dual die package (DDP) technology. This means that an RDIMM-DDP memory module has two DRAM memory chips in a single package. Using this technology allows more memory chips to be placed on a module, which can result in higher overall capacity and/or performance. This is particularly useful in environments that require large amounts of memory, such as servers with virtualization environments or workstations with high memory requirements.

RDIMM-DDP server RAM can usually be mixed with RDIMM standard memory if the server’s memory configuration rules allow it. This allows memory module sizes of 32 GB for RDIMM-DDP in the DDR3 range; 64 GB, 128 GB in the DDR4 range.

The typical memory organizations for communication with the CPU memory controller for RDIMM-DDP modules (Dual-Die-Package-RDIMM module) are 4DRx8 ≙ 2Rx8 and 4DRx4 ≙ 2Rx4.

With the DDP (Dual-DIE-Package), two DRAMs are located next to each other on the board in a DRAM housing.

3.3.3 RDIMM – 3DS (3-Dimensional-Stacking)

With 3DS-RDIMM modules (3-dimensional stacking), the memory is stacked vertically, meaning that several DRAM DIEs are built on top of each other.

All DRAM DIEs of the same level (1H or 2H or 3H, …) together form a rank.

The first DRAM DIE (1H = first level) that is directly connected to the memory board is the master. The master is the only DRAM DIE that communicates with the processor. This is why it is called a physical rank.

The other DRAM DIEs (2H, 3H, 4H, …) are called slaves. They do not communicate directly with the processor and are invisible to the processor.

With 3DS-RDIMM, memory module sizes of 64, 128 and 256 GB in the DDR4 range and 128 and 256 GB in the DDR5 range are achieved.

A notice:

3DS RDIMM modules cannot be combined with standard RDIMM modules or with RDIMM DDP RAMs!

4. LRDIMM – (Load-Reduced DIMM)

Even though the names RDIMM and LRDIMM are almost similar, the two memory formats differ in their functionality and properties. It is therefore not possible to use both memory technologies in one device!

Similar to the RDIMM server RAM, the LRDIMM memory module also has a buffer. It is therefore also a buffered or registered DIMM server memory module. The error correction feature is also present in the LRDIMM memory module.

The small chips among the DRAMs are the special chips of the LRDIMM RAM modules.

4.1 How does buffered RAM work in the LRDIMM module?

LRDIMMs also use buffered RAM to further reduce the load on the memory bus and optimize overall performance. Unlike conventional RDIMMs, which use a single buffer per module, LRDIMMs use a more advanced technology that uses additional chips and logic to reduce the load even further. By merging the data lines in the LRDIMM onto the central memory buffer, an LRDIMM only loads the server like a comparable 1 rank RDIMM memory module.

In practice, this means that in many servers only 4 of 6 memory slots can be used with RDIMM memory, but all memory slots can be used with LRDIMM memory modules. Therefore, the maximum memory configuration can usually only be achieved with LRDIMM memory.

The key difference is that LRDIMMs can support multiple DRAM ranks on a single module. Therefore, buffered LRDIMMs can achieve higher total capacity without compromising performance or stability. This makes them ideal for applications that require a large amount of storage space, such as databases, virtualization environments, and big data applications.

Buffered RAM plays a critical role in providing reliable and high-performance storage solutions for modern server infrastructures. By reducing the load on the memory bus, buffered RAM enables more efficient data transfer while reducing the risk of signal interference and data errors.

4.2 LRDIMM memory: advantages and disadvantages

Advantages:

The advantages of LRDIMM RAM modules are the same as those of RDIMM modules, they only differ in these points:

Highest possible memory density and module count: LRDIMMs offer improved performance in terms of memory capacity and density compared to RDIMMs. They provide greater flexibility in configuration and support for larger total capacities per module, as well as a higher number of modules per system.

LRDIMM modules reduce the load on the server more than RDIMM memory modules and at the same time allow the maximum possible memory. This is not always possible when using RDIMM modules.

Disadvantages:

LRDIMM server RAM modules have similar disadvantages to RDIMM modules. These are higher costs, increased complexity and only compatible with selected devices. In addition, LRDIMM modules cannot be used together with other technologies in a device.

4.3 LRDIMM Variants

LRDIMM – DDP (Dual-Die-Package)
LRDIMM – 3DS (3-Dimensional-Stacking)

4.3.1 LRDIMM – DDP (Dual-Die-Package)

To enable larger memory modules for servers and workstations, other storage technologies are needed.

The LRDIMM DDP memory uses the same technology as the RDIMM type. The Dual-Die-Package technology is explained in detail here.

LRDIMM-DDP server RAM can be mixed with standard LRDIMM memory if the server’s memory configuration rules allow it. This allows memory module sizes of 32 GB for LRDIMM-DDP in the DDR3 range; 64 and 128 GB in the DDR4 range.

The typical memory organization for communication with the CPU memory controller is 4DRx4 for LRDIMM-DDP modules (Dual-Die-Package-LRDIMM module).

4.3.2 LRDIMM – 3DS (3-Dimensional-Stacking)

The 3DS technology does not differ between RDIMM and LRDIMM modules.

The 3DS technology is explained in detail here.

5. Choose the right storage capacity for the server

Memory modules for servers and workstations are generally available with higher capacities than conventional RAM. This is because servers and workstations often have to process large amounts of data. Many users have simultaneous access to, for example, databases, mail systems, terminal servers or web applications. For professional applications with high demands on memory capacity, only server RAM (ECC, RDIMM or LRDIMM) is therefore suitable.

5.1 How much RAM do I need for my server?

This depends on various factors, such as:

Is virtualization such as VMware, Hyper-V, etc. used?
Which server applications or software are running on the server?
Is there a terminal server?
How many users or terminal users access the server?
Are there database systems that require intensive memory usage?
Etc.

5.2 What impact does insufficient RAM have on the overall performance of the server?

If the RAM in the server is too small, this has a negative impact on the overall performance of the system. The result is a noticeable reduction in response speed. This is then shown as follows:

Increased hard disk usage:
If the available memory is not enough to hold all the required data and programs in RAM, the operating system has to resort to the paging file on the hard disk. Since access to the hard disk is much slower compared to RAM, this leads to significant performance losses and delays in data processing.
Increased processor utilization:
The processor utilization increases significantly to compensate for the RAM overload. Applications’ access to data therefore slows down noticeably. In addition, the CPU’s power consumption increases in conjunction with higher power consumption and an increased system temperature.
Degraded multitasking ability:
A lack of memory can affect the server’s ability to perform multiple tasks simultaneously. This can cause some processes to lag or, in the worst case, fail to run at all, affecting the server’s overall productivity.
Instability and crashes:
When server memory becomes overloaded and insufficient, there is an increased risk of system instability and crashes. This can cause applications to terminate unexpectedly or the operating system to crash, which can lead to data loss and downtime.
Limited scalability:
Under-sized server RAM can limit the scalability of the server. When additional resources are to be added to handle increasing demand, a lack of memory can affect the server’s ability to use these additional resources effectively.
Reduced responsiveness and speed:
If there is insufficient memory to support the running processes and applications, the server’s responsiveness may be significantly reduced. Applications may run slower and the user experience will be affected as system response times will be longer.

Insufficient memory significantly reduces the responsiveness and therefore the speed of the entire server system. This not only negatively affects the user experience, but also the productivity and reliability of the server. It is therefore important to carefully analyze the memory requirements of a server and ensure that there are sufficient resources to meet the requirements of the planned applications.

As a guideline, the maximum RAM memory usage should not exceed 70%.

However, if the RAM memory is too large, no negative performance losses are to be expected, because the unused RAM has no disadvantage on the system speed.

6. RAM upgrades for servers: possibilities & limitations

The choice between server RAM and regular memory depends on individual requirements. Server RAM is the best choice for applications that require high reliability, fault tolerance and large storage capacities. Regular memory is sufficient for most home applications and offers good value for money.

6.1 Form factor:

UDIMM ECC (Unbuffered Dual In-Line Memory Module with ECC support): Used in smaller servers.
RDIMM (Registered Dual In-Line Memory Module): With a built-in buffer chip for improved stability, used in servers and workstations.
LRDIMM (Load-Reduced Dual In-Line Memory Module): Enhanced version of RDIMM with additional load reduction for higher memory capacity and speed.
SODIMM (Small Outline Dual In-Line Memory Module): Used in laptops, mini PCs, and other small form factor computers.

UDIMM (Unbuffered Dual In-Line Memory Module): Standard RAM modules without buffering used in desktop computers and smaller servers.

6.2 Clock frequency:

The clock speed of server memory is usually lower than that of traditional RAM. This is because reliability and fault tolerance are more important for servers than speed.

6.3 Compatibility:

Regardless of whether it is RAM for servers or desktop/notebook RAM, it should not be assumed that all possible modules are compatible with each other just because the form factor and clock frequency match.
Rather, it is absolutely necessary to always choose the right RAM for the respective device, which is intended for the model to be upgraded.
On phs-memory.com you will find the right RAM for your device. We will also show you which modules and module sizes are the right ones for your device. Here you will find the maximum possible RAM memory for your device.

In the data sheets and documentation of the manufacturers, the system memory is often stated to be lower than is actually possible. We have observed this effect in thousands of devices and analyzed it in detail.
You can find more information on this topic in our overRAMing project.

6.4 Optimizing server performance / server RAM configuration

More RAM contributes to increased server performance under high loads by making optimal use of free memory resources and not slowing down the system due to RAM that is too small.

Are you still unsure which modules are best suited to your system and requirements? Contact our support and we will help you with this matter.

7. Frequently asked questions about server memory

What is the difference between server RAM and desktop RAM?

They essentially differ in error correction, additional load on the CPU (registered) and price. You can find more details in this article.

What types of server memory are there?

ECC, RDIMM or LRDIMM for DDR3, DDR4 and DDR5 server memory.

Conventional RAM is called UDIMM or SO DIMM.

How can I check my server's memory?

All RAM modules used in servers are error-corrected server RAM (ECC, RDIMM or LRDIMM). This technology automatically monitors the built-in RAM together with the processor’s memory controller and reports errors or defective memory, usually before the system crashes. This technology can even correct 1-bit errors in ECC memory.
Some servers allow the RAM to be checked during the boot process. In the BIOS or UEFI settings, there is a memory test option that runs during system startup and identifies any memory problems.
Some server manufacturers also offer special diagnostic software that can check the hardware status, including the RAM.

Here are some examples:

HP (Hewlett Packard) – HP Insight Diagnostics
HPE (Hewlett Packard Enterprise) – HPE ProLiant Integrated Management Log Viewer
Dell – OpenManage Server Administrator
Lenovo – ToolsCenter
Cisco – UCS Manager

These tools can either be integrated into the BIOS or provided as standalone applications.
If the server manufacturer does not offer any tools, we recommend the Memtest86 program, which is discussed in more detail in this article.

How can I upgrade my server's memory?

On phs-memory.com you can find compatible memory for your server by searching for the server’s model name. In this article you can find out about the differences and properties of the memory modules compatible with your system.

What population rules apply when expanding the memory of my server?

The population rules/matrix for expanding a server’s memory can vary depending on the hardware manufacturer and server model. There are some general guidelines to avoid mistakes and to consider:

Use the model name to find the right server RAM on Speicher.de:
On Speicher.de you will always find the right RAM for your server system. The website shows you the possible memory sizes and possible memory technologies for the server you are looking for.
In many cases you will receive further information on important configuration rules.
If you have any questions about the possible total capacity, upgrading in general or using existing memory modules together with the purchase of larger and new server RAM, you can contact our memory team who will be happy to assist you.
Server manual / server documentation
Consult the server manual or documentation:
Before you begin memory expansion, you should consult your server manual or documentation for specific information on supported memory types, maximum capacities, supported configurations, and population rules.
Identify the supported memory types:
Certain servers only support certain types of memory modules, such as DDR4 RAM or only ECC memory. Make sure that the memory sticks you purchase are compatible with your server’s supported specifications and that the population rules are followed.
Consider the supported capacity per module and per slot:
Check the maximum capacity supported per memory module and per memory slot. For example, some servers may support up to 256 GB per module, while others may only allow up to 32 GB per module.
Consider the number of memory channels:
Some servers use a specific number of memory channels (ranks) for maximum performance. Make sure you distribute the memory bars evenly across the available channels for optimal performance.
Pay attention to the population order:
Some servers require a specific memory module population order to ensure maximum performance. This order may be marked on the board or described in the server documentation.
Mixing memory modules:
In some cases, different sizes of memory modules can be mixed. However, this can quickly lead to performance degradation. It is recommended to use 100% matching memory modules to avoid incompatibilities. It is recommended to always use modules of the same size in the device or to strictly follow the device’s memory population matrix.
Speeds of memory modules
Using memory modules with different clock frequencies in a server is no problem with current devices. The maximum clock frequency is always determined by the CPU used. If the clock speeds are different, the system automatically adjusts to the lowest clock frequency.
Update the server BIOS:
Make sure the server BIOS or UEFI is up to date, as updated firmware versions may provide additional memory support or bug fixes.

If you have any questions about memory expansions for servers, our storage experts will be happy to help you and answer your questions before you make a purchase. Do not hesitate to contact us via the contact form or our telephone storage hotline.

Here you can find help and support.

How can I buy server memory?

Click on our store link from Speicher.de and look for the model drawing of your server. Select the RAM memory you want and add it to your shopping cart.

What is the difference between single-rank, dual-rank and quad-rank memory?

Single-rank, dual-rank and quad-rank refer to the number of memory ranks on a memory module. A rank is a group of memory chips operating in parallel on a memory module.
Here are the differences between single-rank, dual-rank and quad-rank memory modules:

Single-rank memory:
A single-rank memory module contains only one group of memory chips. Single-rank memories generally have faster access times and can access data more quickly than ranks with higher densities.
However, they typically offer less total capacity per module compared to dual-rank or quad-rank modules.
Dual-rank memory:
A dual-rank memory module contains two separate ranks of memory chips.
Dual-rank memory allows for a higher total capacity per module compared to single-rank modules. Because they have two separate ranks, dual-rank modules can potentially offer slightly higher performance when two modules are used in systems that then benefit from an even distribution of memory accesses.
Quad-rank memory:
A quad-rank memory module contains four separate ranks of memory chips. Quad-rank memory offers the highest total capacity per module compared to single-rank and dual-rank modules.
However, due to the higher number of ranks, quad-rank modules can have slightly higher latency as memory accesses must be coordinated between ranks.

Overall, single-rank modules may offer slightly faster speeds, while dual-rank and quad-rank modules allow for higher total capacity per module. The choice between single-rank, dual-rank, and quad-rank memory depends on the specific system requirements and budget, with each option having its own advantages and disadvantages.

Can modules from different manufacturers be combined?

Yes, this is possible. Please note that the guidelines for using the memory are followed: rank number, technology (DDR3, DDR4, DDR5), as well as the specification (LRDIMM, RDIMM, UDIMM, ECC…)

Why do I need error-correcting memory in the server?

With error-correcting storage, you benefit from improved stability, increased scalability, and improved error management.

Can I overclock my server's memory?

Overclocking RAM makes no sense in the server sector, which is why manufacturers do not allow it. The focus is more on stability and quality. Overclocking would be counterproductive here.

How and where do I find compatible RAM for my server?

Depending on the processor technology, which consists of the processor family, generation and category, different RAM is required for the different servers. We have already done this research for you!

On phs-memory.com you can search for compatible RAMs based on your model name. Simply enter the manufacturer, device or article group in the search bar and you will find your device in the list, as well as other helpful tips for buying server RAM.

After you select your model, you will find all the possible options available to you to upgrade the RAM memory.