Answer

The maximum amount of memory that your system can use is actually limited in two ways — not only is there a maximum amount of memory that your computer motherboard can accept, there is also a maximum amount of memory that your operating system (OS) can accept.

For instance, when you install 4GB of memory in a 32-bit Windows operating system (the most common version; 64-bit systems are typically used only by high-end users), your system will see (and utilize) only 3GB or 3.5GB. Is the problem bad memory?

Relax, there isn't a problem with the memory. Windows allows for 4GB of memory to be addressed, but this isn't 100 percent the same as having 4GB of physical memory.

What happens is that some of the addressable memory (regardless of how much you have physically installed) is reserved for use by page files or by some of the devices that you are using, such as a graphics card, PCI card, integrated network connections, etc., so it's unavailable for use as normal main memory.

The amount of memory needed for these devices is calculated by your system at startup; if you haven't maxed out the memory in your system, it's invisible to you, and all your physical memory (the RAM that's installed) is available for use. However if you've maxed out the DRAM in your system, this amount will be deducted from your physical memory, so you can't use 100% of your DRAM.

The maximum memory limitation varies by operating system; for instance, the 4GB memory limitation doesn't exist in 64-bit versions of Windows.

Memory maximums for current Microsoft® Windows OSs include:

Windows 8 (32 bit)

• Windows 8 Enterprise: 4 GB
• Windows 8 Professional: 4 GB
• Windows 8 Home: 4 GB

Windows 7 (32 bit)

• Ultimate: 4 GB
• Enterprise: 4 GB
• Business: 4 GB
• Home Premium: 4 GB
• Home Basic: 4 GB
• Starter: 2 GB

Windows Vista (32 bit)

• Ultimate: 4 GB
• Enterprise: 4 GB
• Business: 4 GB
• Home Premium: 4 GB
• Home Basic: 4 GB
• Starter: 1 GB

Windows XP (32 bit)

• Professional: 4 GB
• Home: 4 GB
• Starter Edition: 512 MB

Windows Server 2003 (32 bit)

• Datacenter SP2: 128 GB
• Enterprise SP2: 64 GB
• Standard SP1: 4 GB*
• Datacenter R2: 128 GB
• Enterprise R2: 64 GB
• Standard R2: 4 GB*
• Web Edition: 4 GB*
• Small Business Edition: 4 GB*

* Certain Microsoft server operating systems can support over 4GB of memory via Physical Address Extension (PAE). Please refer to Microsoft knowledgebase article located here for more information.

Windows Server 2008 (32 bit)

• Datacenter: 64 GB
• Enterprise: 64 GB
• Standard: 4 GB
• Web Server: 4 GB

Windows 8 (64 bit)

• Enterprise: 512 GB
• Professional: 512 GB
• Home: 128 GB

Windows 7 (64 bit)

• Windows 7 Ultimate: 192 GB
• Windows 7 Enterprise: 192 GB
• Windows 7 Professional: 192 GB
• Windows 7 Home Premium: 16 GB
• Windows 7 Home Basic: 8 GB
• Windows 7 Starter: N/A

Windows Vista (64 bit)

• Ultimate: 128 GB
• Enterprise: 128 GB
• Business: 128 GB
• Home Premium: 16 GB
• Home Basic: 8 GB

Windows XP (64 bit)

• Professional: 128 GB
• Windows Server 2003 (64 bit)
• Datacenter SP2: 2 TB
• Enterprise SP2: 2 TB
• Standard SP1: 32 GB
• Datacenter R2: 1 TB
• Enterprise R2: 1 TB
• Standard R2: 32 GB
• Small Business Edition: 128 GB

Windows Server 2008 (64 bit)

• Datacenter: 2 TB
• Enterprise: 2 TB
• Standard: 32 GB
• Web Server: 32 GB

Windows Server 2012 (64 bit)

• Datacenter: 4 TB
• Standard: 4 TB
• Essentials: 64 GB
• Foundation: 32 GB
• Storage Server 2012 Workgroup: 32 GB
• Storage Server 2012 Standard: 4 TB
• Hyper-V Server 2012: 4 TB

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Answer

The term Rank was created by JEDEC, the memory industry’s standards group, to distinguish between the number of memory banks on a module as opposed to the number of memory banks on a component, or memory chip. The concept of memory Rank applies to all memory module form factors, though in general it tends to matter primarily on server platforms, due to the larger amounts of memory they manage.

A memory Rank is, simply put, a block or area of data that is created using some, or all, of the memory chips on a module. A Rank is a data block that is 64 bits wide. On systems that support Error Correction Code (ECC) an additional 8 bits are added, which makes the data block 72 bits wide. Depending on how a memory module is engineered, it may have one, two, or four blocks of 64-bit wide data areas (or 72-bit wide in the case of ECC modules.) This is referred to as Single Rank, Dual Rank, and Quad Rank. Crucial denotes this on the module label as 1Rx4, or 2Rx4, 2Rx8, or similar.

The x4 and x8 refer to the number of banks on the memory component or chip. It is this number, not the number of individual memory chips on a PCB, that determines the Rank of the finished module. In other words, if a module has chips on both sides of the PCB, which makes it dual-sided, it can still be Single Ranked, Dual Ranked, or Quad Ranked, depending on how those chips are engineered.

Since a Rank is 64 or 72 bits, an ECC module made from x4 chips will need eighteen chips for one Single Rank (18 x 4 = 72). An ECC module made from x8 chips needs only nine of them for a Rank (9 x 8 = 72). A module made from eighteen x8 chips would be Dual Ranked (18 x 8 = 144, 144/72 = 2). An ECC module that has twice as many x8 chips becomes Quad Ranked (36 x 8 = 288, 288/72 = 4).

Having a Dual or Quad Ranked module is like having two or four DRAM modules combined onto one module. For example, you can instantly go from four Single Rank 4GB RDIMM to a single Quad Rank 16GB RDIMM (assuming of course the system is compatible with 16GB RDIMMs).

The drawback with higher Ranked modules is that servers sometimes have a limit on how many Ranks they can address. For example, a server with four memory slots may be limited to a total of eight Ranks. This means you can install four Single Ranked modules or four Dual Ranked modules but only two Quad Ranked modules, as installing more would exceed the amount of Ranks that can be addressed.

On matters of Rank and Rank limitations, we recommend that you consult the manufacturer’s documentation for guidelines and directions that apply to your specific system.

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Answer

Crucial makes finding the right upgrade easy. We offer two ways to find the right memory — our System Scanner tool and our Memory Advisor™ tool.

Our System Scanner tool automatically scans your system to tell you about your current memory configuration and recommend compatible upgrades for your specific system.

Or, use our award-winning Memory Advisor tool, where we've compiled all the information you need into one easy-to-use, searchable database. Our Memory Advisor is the most complete tool of its kind, with more than 250,000 solutions for over 50,000 different computers, printers, servers, and more. All you have to do is tell us what system you have, and our Memory Advisor tells you what upgrades will work for you. And we guarantee the memory you buy through the Memory Advisor will be 100 percent compatible with your system, or we'll refund the price of the incompatible module.