Upgrading a Server or Workstation? Read This First!
If you have never purchased or installed memory for a server or workstation, there are additional considerations above and beyond that of normal desktop and laptop computers to keep in mind. These factors are not apparent using detection tools such as the Crucial® System Scanner, so it is important to be aware of them and familiarize yourself with what to watch out for when shopping for upgrades for these more demanding system types. The most common issues reported to us by users caught unaware are outlined below.
ECC versus Non-ECC
Servers and workstations often incorporate memory with added features to check for errors and prevent crashing of programs for improved stability in mission-critical systems. This is referred to as ECC (Error Checking and Correction) memory, which allows the memory to check the integrity of the data for any errors created by interference and fix single-bit errors as it handles data. Non-ECC memory is typically quite stable, but for added peace of mind in systems that must have zero downtime, ECC memory is often preferred. Problems reported by our users usually come from mixing ECC and non-ECC memory, for example when a pre-built system ships with non-ECC memory as a value option and ECC memory is added later. This can work in rare instances, but in most cases your system will fail to complete POST and load into your operating system. Another potential problem is if your motherboard or processor does not support ECC memory, which can also either work but disable the added functionality, or refuse to allow your system to complete startup. The best way to confirm any restrictions on mixing or using ECC memory at all is by checking your motherboard and processor specifications and/or any comprehensive hardware or maintenance documentation for your pre-built configuration.
Registered and unbuffered
Registered memory (RDIMMs), as opposed to unbuffered memory (UDIMMs), features a register on the module that buffers data for a clock cycle between a system's memory controller and a module's DRAM. This reduces electrical load on the components involved and in exchange for slight performance loss, allows a system to address much higher memory totals than unbuffered memory will typically allow for. Almost all registered memory is also ECC, with all the benefits that provides. ECC memory, CPU, and motherboard limitations can prevent registered memory from being fully compatible with your system, though most often with registered parts the system will refuse to start at all if any other component is not fully compatible. Also, registered and unbuffered memory can't be mixed, even in an environment that is compatible with both types of memory.
Memory modules can be single-, dual-, quad-, or octal-ranked. While usually not a factor on standard systems, ranking limitations can present a few complications, particularly when dealing with registered parts. Most commonly, quad-ranked or octal-ranked parts will have specific requirements about how and in what quantity they can be installed in your system's memory slots. Higher-ranked modules can limit how many total modules can be installed, for example, allowing only four out of six memory slots to be populated when any quad-ranked parts are installed, and forcing you to use specific slots in your system if quad-ranked parts are mixed with single- or dual-ranked. Higher rankings can also impact your memory bandwidth, forcing your memory to run at lower speeds when higher-ranked parts are present. This trade off may be required to utilize higher capacities of memory in some systems, though, if single- or dual-ranked parts are not available at capacities desired, or if reduced ranking parts are not compatible with a system at higher memory totals. If none of these restrictions apply, there is otherwise no functional difference between rankings of parts. More details on ranking can be found here.
Load-reduced memory (LRDIMM)
LRDIMMs are an evolution of registered memory featuring a unique memory chip buffer that further reduces electrical load. The result of this is the reduction or elimination of ranking concerns, allowing extremely high totals of memory without performance reduction (or at least diminishing its effect) or any need to avoid filling all slots in a compatible system. Like the relationship between UDIMMs and RDIMMs, LRDIMMs can't be mixed with the other standards without a system refusing to start up properly.
Server memory compatibility can be influenced by the model and quantity of installed CPU. Entry level systems may ship with CPUs which do not support ECC memory, or may not support registered or load-reduced parts. Specific CPUs may also be needed to support higher memory totals. Higher-end servers may also have multiple CPU sockets which need to be fully populated for all memory slots to become available to the system. Refer to your server/workstation documentation for full compatibility and dependency details, and verify your CPU's memory support to avoid any conflicts.
Server and workstation memory, especially RDIMMs and LRDIMMs, are often physically larger than their less demanding counterparts. Besides more components are soldered on the modules, heat sinks are often attached to offset the additional heat generated by this increase in components. While server/workstation boards or the memory risers for them generally account for this in how the slots for RAM are spaced, pay attention to any height needs in your system. Systems with larger CPU fans or other internal components limiting your RAM module height may require purchasing Very Low Profile (VLP) modules to fit alongside other installed components. Some users also prefer VLP parts due to the lower profile allowing slightly improved case airflow and cooling.
A potential issue in any computer is running an outdated BIOS, but servers and workstations especially work best when running your system's most recent BIOS. As newer technologies are introduced in RAM components, BIOS updates become increasingly likely to be required to run higher memory totals.
If you are unclear on any of the above, your motherboard or system manufacturer and Crucial Support can assist you further. Multiple contact methods for Crucial are available here to help ensure the right parts are selected for your needs.
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