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

What is my computer model?

Make and model. It's easy if you're talking about your car — not so easy when you are talking about your computer. Sure, you know if you've got a desktop or laptop. And you know the manufacturer. But beyond that, model specifics can get confusing. When finding a compatible memory upgrade, knowing your exact model is important — here is how to figure it out.

Are you upgrading the computer you are working on right now?
That's easy. Use the Crucial System Scanner. This downloadable tool determines the memory in your computer and tells you what your computer needs. Don't worry — no spyware or anything like that. The tool just looks at the technical, boring details of your system motherboard.

Start here.

How does it work? Watch this video.

Are you upgrading a different computer?
You can use the Crucial Memory Advisor. In just three clicks, we can tell you what memory upgrades are available for your system. But, you will need to know the make and exact model.

If you're using a Windows-based system, the model will be specified on the label, a small sticker on the back or

side of your desktop system, or the bottom of your laptop.

If you can't find the label, you can find model information this way.

Start ==> My Computer ==> Right click ==> Properties.

Or for more detailed info go here:

Start ==> Run ==> Dxdiag

You'll see "System Model" — that is the specific model of your computer and the information you'll need to use the Crucial Memory Advisor.

On a Mac system, you can find your system by first going to the Apple icon on the top left.

About this Mac ==> More info

Once you've determined the model, use the dropdown menu on the Crucial Memory Advisor to determine compatible upgrades.

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For more information on DRAM, go to our Knowledge Base library or our news and information page. For additional information on Crucial DRAM products, go to our product pages or support center.  We have lots of videos for you to watch on our YouTube Channel. And if you’re ready to take the plunge, use the Crucial Memory Advisor or the Crucial System Scanner.